see also the pile of docs in http://www.ices.utexas.edu/~organism/high-school-science-projects/ scientific method calibration, validation, prediction verification "making materials" category more technology than science but, hey, it's cool in addition to making a material, write a history paper on the various methods used (and once used) but there is materials science: what modern materials can we experiment with? millikan oil drop experiment (e) are "cathode rays", beta-rays, and electrons all the same? experimental determination of G torsion fiber w/dumbells at end (w/ and w/o lead spheres nearby) exp det of c - interference fringes - no ether (rotate interferometer) exp det of \epsilon_0 and \mu_0 (to infer c) exp det of speed of sound - standing wave in a tube? (open and closed) exp det of h - photoelectric effect? waves semicircle: whisper around edge, reflection back to center cylinder w/speaker and sawdust marshmallows in microwave delayed feedback and cognitive dissonance when speaking einstein/deHaas's electron spin / ferromagnetism connection piece of demagnetized iron on end of thin wire; attach mirror(s) to iron apply magnetic field to iron; observe oscillations using laser pointer reflected from mirror p69 in sep 2004 issue of sci am high-altitude balloon photography/videography why fashion (finite) parabolic reflectors cloud chamber rubbing alcohol in petri dice in bath of dry ice (ethanol? methanol?) thorium gas lantern mantel; americium smoke detector; uranium ore powder; radium from old luminous clock dials paper chromatograph / electrophoresis coffee filter design from sciam? dyes, inks, flowers, etc fractional distillation column petroleum, volatiles from flower scents (whatever's common to get a *lot* of flower heads) build an x-ray generator with a light bulb filament, some aluminum foil, and a tesla coil build a laser CO2, HeNe, Cu vapor, Ar ion, Nd & YAG, ruby demo of conservation of mass in chemical reactions zinc pennies in vinegar weigh the vinegar and pennies separately before weigh the copper and the vinegar (vinegar solution now!) after "what's in the vinegar? (after the reaction)" can this be done? http://www.nytimes.com/2009/04/30/business/businessspecial2/30solar.html microfluidics using shrinky dinks and PNAS paper can this be used to make photolithography masks? or other optical instruments? kristian birkeland's experiments on the aurora use a cathode ray gun to shoot electrons at a magnetized (steel) sphere do this in a (mostly) evacuated chamber (maybe w/a low partial pressure of neon?) old TV tube with the screen degaussed? http://dx.doi.org/10.1007%2FBF02559599 -- carl stormer's obit paramagnetism and diamagnetism experiments dip a disk of gadolinium in liquid nitrogen acoustics of drums why does a kettle drum have a distinctive tone? phys today 45(3), 40--47, mar 1992 surface area shape of the earth - coriolis forces and ballistic tracking - walk around the earth with a gyroscope - other astronomical expts to determine size of earth, moon, sun, planets and their (relative) distances how do computers work disspation of ocean waves tidal locking of satellites biz baz buz irrationality of sqrt(2) and pi transcendentals - liouville's number doilies sneakernet vs ethernet truck full of DVDs vs internet2 cross country stone tablet through space vs sending weak signal (w/correspondingly longer error-correction scheme) through space olive oil drop on water compute thickness = volume/area avogadro's number from def'n (mass/MW=moles; assume thickness=radius) (the assumption thickness=radius means we get a measurement of a molecule's diameter as a bonus here) verify thickness using interference minopoli introduction "whoa, look at it go!" mountains of molehills einstein's 1905 PhD thesis used a model of a dilute suspension of small spheres in a fluid to calculate changes in the fluid's viscosity; the change depends on the diameter of the spheres approximating sugar molecules as spheres and using tables of viscosities of sugar solutions, arrived at an estimate of sugar molecule size see sec 1.1.34 of "Mechanics of periodically heterogeneous structures" by Manevitch, Andrianov, Oshmyan, eds; along with referenced subsequent secs can it be extended to long, thin rods? (oil in alcohol?) (no tangling in a shear flow? (but yes in uniform flow) ) apply to soap in clean water to get (2x) length of soap molecules? compare with olive oil on water experiment result? avogadro's number discussion below from sci am injection of molasses between two plates (w/ and w/o obstructions) saffman-taylor instability / viscous fingering flow in porous media non-fickian diffusion rayleigh instability? reversibility of stokes flow dye drop in glycerine pass a paddle back and forth even a mesh works! one can also rotate the paddle CW and then CCW see fig 2.6 on p32 of acheson (elementary fluid dynamics) also section 7.4 - refs chaiken et al 1986; ottino 1989a proc r soc london A 408, 165-174, 1986 scientific american 260(1), 40-49, 1989 anti-bubbles marangoni convection silicone oil w/metal filings to show convection cells hot coffee/tea/water with fresh lemon/orange (peel!) in a styrofoam cup oil from the fruit is a solvent; it'll soften the styrofoam http://www.newton.dep.anl.gov/askasci/chem98.htm "Casting bronze using a domestic microwave oven" http://home.c2i.net/metaphor/mvpage.html "Research is nearing completion on a system that will allow the melting and casting of bronze, silver, gold, and even cast iron, using an unmodified domestic microwave oven as the energy source. A potential foundry in every kitchen !!" can you use this to melt tin and make float glass? cullet only needs to be heated to about 600oC whereas virgin materials need to be heated to over 1500oC. (but materials are readily available including baking powder, sand, and limestone for soda-lime glass. do other virgin glasses need to be heated so hot?) make a Prince Rupert's drop: a small glass ball with a long tail formed by dropping molten glass into water. You can pound on the ball end with a hammer and it will not break, but snip off the tail and the ball will explode into tiny pieces as the tensile forces are released. demo annealing and tempering in addition to making the glass, write a history paper on the various methods and materials used (contemporary and past) use three plastic bottle caps to support an inverted drinking glass in the center of a microwave. stick a toothpick in a piece of cork (or other non-conductive material that'll act as a support base). light the toothpick and place under the glass. turn on the microwave. a plasma will be generated in the exhaust of the flame. build a farnsworth fusor or a hirsch-meeks fusor http://en.wikipedia.org/wiki/Farnsworth-Hirsch_fusor http://en.wikipedia.org/wiki/Fusor can crusher / coin shrinker (quarter shrinker) http://www.teslamania.com/ (bert hickman) http://www.altair.org/crusher.html http://www.powerlabs.org/pssecc.htm (sam borros) http://members.tripod.com/extreme_skier/cancrusher/ (tristran) http://members.tm.net/lapointe/Main.html (bob lapointe) http://en.wikipedia.org/wiki/Pinch_%28plasma_physics%29 physics demonstrations: a sourcebook for teachers of physics julien sprott (see his web site too: sprott.physics.wisc.edu) peter j. collings liquid crystals: nature's delicate phase of matter 2nd ed, 2002 ????? tomas bohr, may 5 2006, physical review letters liquid in a cylindrical canister w/open top whose walls rotate will form a vortex; if the vertical wall is fixed and the bottom spins, the simple vortex is unstable at high enough rotation rates; it will transition to a new stable state as the speed is increased - that state is roughly triangular in shape; this shape too is unstable at even high speeds; the next stable state is square shaped which, in turn, is unstable at even higher rates; the next stable state is pentagonal (and so on...) technical university of denmark Nature, Published online: 19 May 2006; | doi:10.1038/news060515-17 Geometric whirlpools revealed Recipe for making symmetrical holes in water is easy. Philip Ball Bizarre geometric shapes that appear at the centre of swirling vortices in planetary atmospheres might be explained by a simple experiment with a bucket of water. refs (bohr plus two others) integrate with a shop class have a physics/chemistry class visit the shop to learn about machine tools, glassblowing, and whatnot, and what's possible in the shop and what's not have the shop class visit the lab to see the experiment in operation; have the lab class as an exercise try to explain the operation and results of the experiment to "the public" hybrid liquid/solid rocket engine june/july 2007 issue of airspacemag.com about tim pickens cornstarch and water as a non-newtonian liquid fill a kiddie pool with it and run across watchglass sitting on a transducer 120 Hz @ somewhere in the range of 0-30g acceleration produces faraday waves at 15g you can blow a hole that doesn't collapse; multiple holes will interact at 25g when you disturb the surface, the perturbation grows (some monsterism) pour super-cooled water from a bottle and watch it solidify as it impacts (-21C) bottled water from the store in a deep freezer? demonstrate the bellows conjecture (theorem) with a rigid flexihedron and a real bellows build tesselations with cardboard and/or straws http://www.geocities.com/Heartland/2955/swimming_hole.html Swimming Hole Problem A person is jumping into a swimming hole by holding onto a rope suspended, as from a tree, over the water, swinging out, and releasing the rope. After releasing the rope the person has a certain velocity vector V, travels in a ballistic (parabolic) arc until splashing down into the water. The rope is suspended from a point which is h units above the water, and the rope is of length l. At the dock, the rope makes an angle THETA from the vertical (THETA << PI/4); the person releases the rope when it makes an angle PHI from vertical (PHI < THETA). Question At what angle PHI should the person release the rope? * to maximize distance from dock to landing point? * to maximize time in free fall? * to maximize time from leaving the dock to splashdown? * to maximize apogee height? In general, describe the path in closed form. Note that the first part of the path is circular, the second part is parabolic. Please don't say PHI should be 45? since THETA isn't even that much. Make any simplifying assumptions. Assume the person is spherical and point-size, the rope is rigid and massless, sine(THETA) = THETA, and so forth. Ignore air resistance. Assume a constant gravitational acceleration, and a non-rotating earth. To start, assume the height h is equal to the length l, that is the center of mass of the person skims the water at the bottom of the pendulum swing. Please let me know. I don't have any solution to this problem. This problem was posted to alt.math.recreational on January 25, 1999, as message . another cool geometry problem http://www.math.niu.edu/~rusin/known-math/98/5pt.cyl http://www.math.niu.edu/~rusin/known-math/polyhedral/flexible.polyh/welcome.html mathworld - ArchimedianSolid.html http://math.cornell.edu/~connelly/ the irrationality of \sqrt{2}, \pi, e the liouiville number is transcendental (approximibility of algebraic numbers) brachistochrone problem catenary form (approx by parabola) verheyen, h.f. "the complete set of jitterbug transforms and the analysis of their motion," in computers, math, and applications. 17(1-3), 203-250, 1989. near-earth solar-like objects image faint objects w/long exposure times and use parallax The mathematics of soap films : explorations with Maple. / Oprea, John / Providence, RI / 2000 QA 644 O67 2000 Physics-Math-Astronomy Library Subject: measurement of drainage curves why is mercury used? or rather, why did it used to used? is it still used? was it used because of the low surface tension? would liquid CO2 be a suitable replacement? what does the experimental set-up look like? Why does shaking a can of coffee cause the larger grains to move to the surface? H. Kanchwala Pune, India Heinrich M Jaeger, a professor of physics at the University of Chicago, explains. The phenomenon by which large grains move up and small ones move down when shaking the can is called granular size separation. It is often referred to as "the Brazil nut effect," since the same result occurs in a shaken can of mixed nuts. There are several physical mechanisms that can give rise to size separation. Obviously, the very finest (dust-like) grains might just fall down through the cracks left between the larger particles. The more interesting case concerns mixtures of particles that do not differ all that much in size, perhaps by as little as 10 percent. Surprisingly, in this case the larger (and thus heavier) ones still end up near the top. Two main mechanisms give rise to this separation. Firstly, if during a shaking cycle (as the material lifts off the bottom of the can and then collides with the bottom again) the large particles briefly separate from the surrounding smaller ones and leave a gap underneath, small grains can move into this opening. When the shaking cycle is finished the large particles are prevented from getting back to their original positions. Thus, the bigger particles are slowly "ratcheted" upward. Secondly, the granular material rubs against the sidewalls of the can when it is shaken. This friction causes a net downward motion of grains along the walls. This downward flow occurs in a narrow region only a few particle diameters wide close to the walls. In the center of the can, meanwhile, the particles move up, completing a convection roll. Large grains, just like any other grains, are moved up along the center (similar to being on an escalator). Once they reach the top they move toward the side wall and try to enter the downward flow. But if they are too large, they cannot fit into the narrow region that contains the downward flow and they get stuck near the top. After a few shaking cycles, this leads to an enrichment of large particles near the top. Both mechanisms can apply simultaneously, in principle, and both will lead to the same net effect: large particles will end up near the top. Differences between the two mechanisms are somewhat subtle. For example, the speed with which the larger particles rise to the top surface is different in the two scenarios. In practice, the second mechanism, known as a convective mechanism, dominates the first mechanism as long as the sidewalls are not frictionless (which is hard to achieve), and as long as you are considering particles not too deep below the surface. One further remark: if the particle size is very small (smaller than, say, one millimeter) the presence of air can modify both mechanisms. How this occurs in detail is still an open question and the focus of much research at the moment. Fluid Flow At its annual meeting last fall, the American Physical Society's Division of Fluid Dynamics selected a short video by Markus Zahn, professor of electrical engineering, and Cory Lorenz '03 as one of five winning entries in its Gallery of Fluid Motion. The video, which captures the pair's discovery of a ferrofluid's unusual ability to flow into complex designs, will be featured in the September 2003 issue of *Physics of Fluids*. It will appear alongside the other winning entries, which include a video by mechanical engineering professor Gareth McKinley, PhD '91, and a poster by associate mathematics professor John Bush. The gallery was an assemblage of 25 poster and video entries that demonstrate fluid flow phenomena. Entries were judged on such criteria as originality, the ability to convey information, and artistic content. Zahn and Lorenz's groundbreaking video show a drop of ferrofluid -- liquid contatining magnetic particles -- that has been placed between two glass disks. The liquid, which is normally stable, responds to magnetic attraction. When Zahn and Lorenz apply two magnetic fields, the drop changes shape to resemble cartoon-like doodles. At the meeting, Zahn observed attendees' reactions to the video. "You could hear people under their breath go, 'Wow,'" he says. Ferrofluids are commonly used as sealants on computer disk drives to keep out dust. However, Zahn '67, SM '68, EE '69, ScD '70, is currently working with several students to apply this research to microfluidic and microelectromechanical devices, and to understand why the ferrofluid forms such intricate patterns under these conditions. public_html/fluids/ferrofluid.jpg http://www-math.mit.edu/~bush/ http://www-math.mit.edu/~bush/gallery.html http://web.mit.edu/nnf/ electrohydrodynamic and electrokinetic interactions with charged and polarizable fluids; ferrohydrodynamic interactions with magnetizable fluids A Drop to Drink Each year, water-borne diseases kill an estimated three million people and sicken more than two billion more. One method of decontaminating disease-fouled water uses solar rays, but it works only in parts of the world that get plenty of sunlight. Now an MIT doctoral candidate has found an efficient way to determine whether solar disinfection will work in a given area. For his master's project in civil and environmental engineering, which he described in the January issue of *Water Research*, Peter Oates, Mng '01, developed a mathematical model that suggests that in Haiti, solar disinfection can be used year-round. He "went to the NASA data that averages the amount of solar radiation on the the planet and came up with a simple model to predict whether it is worth looking into solar disinfection in a given region," says Oates's advisor, Professor Martin Polz. Solar disinfection relies solely on the heat and ultraviolet radiation of the sun to make water stored in transparent containers drinkable. Oates says MIT students have used his model to evaluate solar disinfection for other regions, including Nepal. But he favors prudence when using it. "Because we're dealing with human health, I would err on the cautious side," he says. Starry, Starry Night Astronomy enthusiast Anthony Ayiomamitis documented the solar analemma in "Sunrise Analemma with the Tholos (360-350 B.C.) at Ancient Delphi, Greece," (right) by photographing the sun over the course of 2002 at the same time each day on a single piece of film, a feat of astro-photography accomplished only seven times since the first imaging of the analemma in 1979. "As a result of the earth's tilt about its axis -- 23.5 degrees -- and its elliptical orbit around the sun, the location of the sun is not constant when observed at the same time each day over 12 months," he writes. "This loop will be inclined at different angles depending on one's latitude." The figure-eight shape traced by the changing of the sun's position has been represented on sundials and on older terrestrial globes, where it symbolized the changing seasons. public_html/images/solar-analemma-ayiomamitis.jpg http://www.fieldlines.com/other/diamag2.html This page shows some experiments with a small wooded diamagnetic levitation stand which uses Carbon graphite blocks. You may have seen our other page in which Bismuth was used. The stand itself is simple; it has a large magnet overhead attached to a threaded shaft. (See the picture below.) In this stand we used a large Neodymium Iron Boron magnet, although less expensive ceramic magnets seem to work just as well. Below are two Carbon graphite blocks. One is glued to the base, while the other is attached to one of the vertical dowels so that it can be raised, lowered, or turned away if not used. The Carbon graphite works every bit as well as Bismuth for this demonstration, and is considerably less expensive. We would advise anybody building a stand like this to coat the Carbon graphite with some clear enamel or other coating to keep the graphite from rubbing off. It can be rather messy! Some Carbon samples are more diamagnetic than others, but these blocks are the best we have seen. They are available on our products page. big magnet (gap) graphite block small (but strong) magnet graphite block http://www.lipsons.pwp.blueyonder.co.uk/mathlego.htm lego models of mathematical surfaces http://www.lipsons.pwp.blueyonder.co.uk/lego.htm also on home page: models of escher drawings, rodin's thinker Galileo's ball drop experiments dropping a feather and a hammer put the feather in a bell jar, and evacuate the air gold is far denser than water faraday - in the 1850s - made a gold suspension in water that still today sits in the museum at the royal institute in london. particles smaller than one micron but bigger than one nanometer??? http://personal.bgsu.edu/~tweney/ More recently, similar measurements have been made, not using optical light but radio waves. These have the advantage that they are not scattered by the atmosphere like optical light is. The light-bending measurement for radio sources rather than stars can be made almost at will, without having to wait for an eclipse. For example, every year the distant quasar 3C279 passes behind the Sun, producing a measurable deflection. These measurements confirm the Einstein prediction and it is now accepted by the vast majority of physicists that light is bent in the manner suggested by the general theory of relativity; a quantitative summary of many experimental tests can be found in Bertotti et al. (1962). Bertotti, B., Brill, D.R., & Krotkov, R. 1962 in Gravitation: an Introduction to Current Research, ed. L. Witten (New York: John Wiley & Sons), 1 MIT researchers reported in the Aug. 7 issue of "Nature" that they now understand how the insects known as water striders skim effortlessly across the surface of ponds and oceans. For more, visit http://web.mit.edu/newsoffice/rd/2003/sep.html ------------------------------------------------------- For immediate release: February 12, 2004 Editors: Photos are available at: http://www.princeton.edu/pr/news/04/q1/img/Chaikin-Torquato/ Sweet science: Common candies yield physics discovery Research using M&M's sheds light on particle-packing problem PRINCETON, N.J. -- For most people, a regular lunch of M&M's and coffee would lead to no good. For Princeton physicist Paul Chaikin and collaborators, it spurred fundamental insights into an age-old problem in mathematics and physics. Chaikin and Princeton chemist Salvatore Torquato used the candies to investigate the physical and mathematical principles that come into play when particles are poured randomly into a vessel. While seemingly simple, the question of how particles pack together has been a persistent scientific problem for hundreds of years and has implications for fields such as the design of high-density ceramic materials for use in aerospace or other applications. The researchers discovered that oblate spheroids, the shape of M&M's chocolate candies, pack surprisingly more densely than regular spheres when poured randomly and shaken. Extending the work with further experiments and sophisticated computer simulations, they found that a related shape, the ellipsoid, packs at random even more densely than the tightest possible, perfectly ordered arrangement of spheres. Previously, scientists did not know that randomly assembled particles could pack so densely. "It is a startling and wonderful result," said Sidney Nagel, a physicist at the University of Chicago. "One doesn't normally stop to think about this. If you did, you might have guessed what would happen, but you'd have guessed wrongly." The researchers published their results in the Feb. 13 issue of Science magazine. A surprising element of the results is that the small change from sphere to spheroid -- one is just a squashed or stretched version of the other -- produced a major change in the random packing density. When poured randomly, spheres occupy about 64 percent of the space in the container. M&M's, by contrast, achieve a density of about 68 percent. In non-random packings -- those that are laid out in regular repeating patterns -- changing from sphere to spheroid has no significant effect on the packing density. "We just stretched a sphere and suddenly things changed dramatically," said Torquato. "I think that is remarkable." The reason for the effect, the researchers proposed, is that distorted particles act like little levers and pivot when they push into one another. When the particles turn, the cluster becomes unstable and has to pack tighter before becoming jammed. Perfect spheres do not tend to turn and would remain equally stable even if they did. The study of particle packing dates to the 16th century when physicist and mathematician Johannes Kepler investigated ordered arrangements of spheres. It was not until 1998 that a mathematician proved that the densest possible arrangement of spheres fills 74.04 percent of the total space, as Kepler had predicted. The packing of randomly assembled particles is less well understood. "There is still a tremendous intellectual puzzle in the way things like M&M's pack together," said Sir Sam Edwards, a physicist and authority on granular materials at Cambridge University. He said the new result is a "nice step forward" in clarifying the relation between particle shape, packing density and the methods used for pouring and shaking. Chaikin and Torquato have had a longstanding interest in particle packing, but their work on spheroids stems from Chaikin's longstanding interest in M&M's. His students, poking fun at his affection for M&M-fueled lunches, sneaked a 55-gallon drum partly full of the candies into his office. Years later, after developing an apparatus to examine certain properties of sphere packings, he asked an undergraduate student, Evan Variano (now a graduate student at Cornell University), to measure the density of random-packed M&M's. M&M's happen to be almost perfect spheroids and are extremely uniform in size and shape, said Chaikin. "I didn't believe the results for some time and finally I just did it myself," Chaikin said. "And, of course, Evan was completely right: They packed a lot better." Another student, Ibrahim Cisse, meticulously counted the contact points between the candies by pouring paint through the container and looking for paint-free dots where candies touched. The researchers then needed to assure themselves that the candies were not somehow assuming an ordered, crystalline arrangement in the center of the container. At the University Medical Center at Princeton, they did an MRI scan of the container and proved the M&M's were oriented randomly. To more fully understand the particle behavior, Torquato and his student Aleksandar Donev developed a computer simulation that allowed them to test any shape, from a flattened M&M-like shape to a sphere to an elongated cigar-like shape. The computer model yielded a further surprise when they stretched the M&M shape so it looked elliptical from the top as well as from the side (like an almond M&M). That shape, an ellipsoid, achieved a random packed density of nearly 74 percent (higher in subsequent studies). "That blew us away," said Chaikin. "Nobody had ever gotten random packings anywhere near crystalline packings, and this is above." Random packings of spheroids and ellipsoids also have greater numbers of contact points with their neighboring particles, the researchers found. Their evidence suggests that the number of contact points varies in proportion to the number of directions the particle can move or pivot. Chaikin, Torquato, Variano, Cisse and Donev co-wrote the Science paper with former undergraduate David Sachs, visiting research collaborator Frank Stillinger and Robert Connelly, a professor of mathematics at Cornell. The researchers plan to continue their investigations, which could ultimately prove important to any field involving granular materials, from molecules and cells to grain in a silo. Materials scientists, for example, make high-performance ceramics by fusing powders made of tiny particles. A more tightly packed powder with many contact points could yield a less porous ceramic, the researchers said. The researchers also believe the work may shed light on an important class of substances that combine properties of liquids and solids. These materials, known as "glasses," consist of randomly assembled molecules, as in liquids, but are hard. A glass is like a liquid whose molecules become "jammed" into solid state. "The precise connection between jamming and disorder is a deep and open question," Torquato said. "To me, it's remarkable that you can take this simple system with common candies and probe one of the deepest problems in condensed matter physics," Torquato added. In the meantime, Torquato and Chaikin expect to do very well in Valentine's Day contests to guess how many candies are in a container. You can too: If the candies are chocolate M&M's, estimate the volume of the container in cubic centimeters and multiply by 0.68. Divide by 0.636 cubic centimeters, the volume of a single plain M&M candy, and you have the answer. M&M is a registered trademark of Mars Inc. The company has no financial ties to the research, although it did donate 125 pounds of almond M&M's to Chaikin. The work was supported by the National Science Foundation, the National Aeronautics and Space Administration and the Petroleum Research Fund. --------------------------------------------------------------- Accurate determinations of Avogadro?s number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement. This became possible for the first time when American physicist Robert Millikan measured the charge on an electron. The charge on a mole of electrons had been known for some time and is the constant called the Faraday. The best estimate of the value of a Faraday, according to the National Institute of Standards and Technology (NIST), is 96,485.3383 coulombs per mole of electrons. The best estimate of the charge on an electron based on modern experiments is 1.60217653 x 10^-19 coulombs per electron. If you divide the charge on a mole of electrons by the charge on a single electron you obtain a value of Avogadro?s number of 6.02214154 x 10^23 particles per mole. Another approach to determining Avogadro?s number starts with careful measurements of the density of an ultrapure sample of a material on the macroscopic scale. The density of this material on the atomic scale is then measured by using x-ray diffraction techniques to determine the number of atoms per unit cell in the crystal and the distance between the equivalent points that define the unit cell (see Physical Review Letters, 1974, 33, 464). sciam ask the experts The Tamarack Mines Mystery By Donald E. Simanek http://www.lhup.edu/~dsimanek/hollow/tamarack.htm using a plumb line to estimate the curvature of earth's surface what about using plumb lines down a stairwell use an interferometer to measure distances between plumb lines use a laser as a third/reference "plumb" line (it may not go straight down) the wire line w/bob will swing back and forth measure (period and) mean about the reference/center for both a pair of laser lines would have to be parallel measuring deviance wouldn't be easy (?relative interference top and bottom?) accounting for centripetal accel wire lines light line? leidenfrost point (see leidenfrost-essay.pdf by jearl walker, cleveland state u) dry quicksand detlef lohse, university of twente, netherlands by blowing air through sand to fluff it up, and letting it settle, they were able to reduce the packing density of the sand grains to 41% (from 60%) further by letting a weighted ping pong ball come gently to rest on the surface, the sand swallows the ball whole, emitting a "burp" of a sand jet if the ball is sufficiently heavy (cool photo sequence) published in Nature, 432, 689 - 690 (09 December 2004) ------------------------------------------------- Researchers explore mystery, and say gotcha Video, computer modeling reveal flytrap's trick By Gareth Cook, Globe Staff | January 27, 2005 A team of scientists led by a Harvard mathematician announced yesterday that they had solved one of the plant world's most intriguing mysteries: how the Venus flytrap snaps shut. At least since Charles Darwin, scientists have been puzzled by the carnivorous plant, which can close its fanged leaves on an insect in a fraction of a second -- without any muscle. Using a high speed video camera and computer modeling, the team found that the flytrap employs an ingenious trick to slowly build up elastic pressure in its leaves, like the stretching of a rubber band, and then snap at the slightest provocation. The flytrap experiments, which brought together mathematicians, engineers, and biologists, are part of a growing interest in biomechanics as engineers design devices as small as cells and look to nature for inspiration. But the real driving force behind the work was something that may seem quaint in an era of particle accelerators and interplanetary space probes: curiosity about the everyday world. For Lakshminarayanan Mahadevan, who led the team, the discovery joins a list of projects that have brought surprising insights, and publications in high-powered scientific journals, on topics as seemingly mundane as the crumpling of paper and the pouring of honey. "People assume that because it is familiar it is understood," said Mahadevan, who is a professor of applied mathematics and mechanics. "But if you really probe, there are mysteries." Darwin himself considered the Venus flytrap a worthy mystery, declaring in the 19th century that the plant was "one of the most wonderful in the world." In the many years since, plant biologists uncovered some pieces to the puzzle of the flytrap. Although plants do not have a nervous system in the conventional sense, they are able to send signals in the form of electrical pulses. Studies of the Venus flytrap showed that it, too, used such pulses, explaining how it might send the signal to close when an insect crosses one of the tiny filaments on the leaf. Scientist have long suspected that the plant creates forces on the leaf by moving water into certain cells, or by changing the strength of the walls that surround the cells, said Mahadevan. Denying water to a common house plant, for example, will make its leaves move: They wilt. The question has been how the flytrap can move before its prey buzzes along, because it seemed impossible that the plant could create such force so quickly. To find an answer, the team painted a field of dots on the outside of the leaf, according to the paper, which is published in today's issue of the journal Nature. From a video of the leaves clamping shut, they then tracked the path of each of the dots. This, in turn, allowed them to reconstruct the shape of the leaf at each moment, and build a computer model of the entire process. The plant's secret lies in the elasticity and curvature of its leaf, which is somewhat analogous to a soft contact lens. When a contact lens is pushed, it first holds steady, and then dramatically flips around. Strain within the Venus flytrap leaf, probably created by water pressure, keeps the leaf poised near the point at which it will flip. Then, when an insect lands on the leaf and triggers an electrical signal, it takes only a tiny change in pressure to push the leaf over the brink, slamming it shut. "Their contribution is to explain, in beautiful detail, how the mechanical structure actually operates," said Karl J. Niklas, a professor of plant biology at Cornell University. The exact mechanism the flytrap uses to change the pressures within the leaf remains unknown, Mahadevan and other scientists said. Mahadevan said that the team, which included Yoel Forterre of the University of Provence in France and Jan M. Skotheim and Jacques Dumais of Harvard, did not envision any immediate application of the work. But the insight might prove useful in microfluidics, a relatively new field concerned with creating devices that manipulate the flow of very small amounts of liquids and gases. The plant's ability to create a dramatic movement, without muscle, might inspire designs for such devices, Mahadevan said. Gareth Cook can be reached at cook@globe.com --------------------------------------------------------------------- ian stewart, sci am ???daisy give me your answer do??? ???january 1995??? http://www.sciencenews.org/articles/20070505/mathtrek.asp science news magazine Week of May 5, 2007; Vol. 171, No. 18 The Mathematical Lives of Plants Julie J. Rehmeyer Subject: mail fellow about fib and flowers "no nonsense in finding fibonacci numbers in flowers" dear dr. simanek, i recently read many of the articles you've posted on the web. i really appreciate your debunking pseudo-science, humor, ?. debunk the debunking. http://www.lhup.edu/~dsimanek/pseudo/fibonacc.htm You don't need biology to produce spirals such as those found in sunflower seeds. ... The reason is simple. The growth pattern of the seed head (and our constructed spiral) is such that it is biased to povide reasonably close packing of the seeds (or washers) consistent with the growth processes. close packing => golden angle It seldom comes out perfect in the sunflower, and when it is nearly perfect, those are the seed heads which get photographed. lucas series, injuries (insects and other animals; weather) The reason f shows up in nature has to do with constraints of geometry upon the way organisms grow in size. Irrational numbers (those which cannot be expressed as a ratio) are often revealed in this process. again, close packing => golden angle cite ian stewart. scan of article. ------------------------------------------------------------- Subject: chem links http://www.csufresno.edu/Chemistry/welcome/chemfacts.html www.csufresno.edu/chem/ www.csufresno.edu/chem/chemfacts.html http://crystal.biol.csufresno.edu:8080/chemfacts.html http://crystal.biol.csufresno.edu:8080/ Chemistry Factoids A World Wide Web Site Created by Students in Chemistry 1 Chemistry: Its impact on Society Fall 1996 - Fall 1998 California State University, Fresno Welcome to the chemistry factoids page! Here we have collected World Wide Web articles written by students in Chemistry 1. Chemistry 1 or "Chemistry: Its Impact on Society" is one of our department's introductory chemistry offerings which satisfies the physical sciences general education requirement. The catalog description of this and other lower division chemistry courses is also available. These articles discuss chemistry-related questions which are relevant to our everyday lives. Articles are organized by topic. Take a few minutes to look around! A disclaimer: Please be aware that these are student projects, produced as an educational exercise for the class. These articles were not written by experts on the topics and may contain errors. This is a searchable site, thanks to Matt's Script Archive. Use this simple keyword search engine to search the Chemistry Factoids Site. You may send comments to the chemistry factoids page by sending electronic mail to the instructor: kimberly_lawler@csufresno.edu. A description of the Chemistry 1 Web Site Project is available in the course handout from Fall 1997. See also: Dr. Lawler's Home Page. A note: Each article contains 2-3 links to other web sites. Some of these on-line references may no longer be active. We have choosen to leave the articles "as is", since updating the links would be modifying the student-produced work. Plants and Pesticides * What is in those new flea control products for pets? * Why was DDT so harmful? * What are the primary nutrients provided to plants by fertilizers? * What are PCB's? * What are the most common pesticides in use today? * What are the effects of pesticide poisoning? Automobiles and fuels of all kinds * What is natural gas? * What does the octane rating of gasoline mean? * What is coal composed of? * What chemistry is involved in airbags? * What is diesel fuel and how is it different from non-diesel fuel? * What happens to crude oil at the refinery? yadda yadda yadda -------------------------------------------------------- GLOBE EDITORIAL Why? February 2, 2005 RESEARCH EXPLORING how the Venus flytrap snaps shut on its prey may not win a Nobel Prize, but scientific curiosity can be its own reward, leading to serendipitous discovery as well as making the pulse race a lot more frequently than the lightning-strike call from Sweden. Lakshminarayanan Mahadevan, Harvard University professor of applied mathematics and mechanics, who led the team that published its carnivorous plant findings in the journal Nature last week has made a career of looking into things just because they're interesting. His philosophy should be inspiration to educators seeking to ignite young minds, and to anyone who wants to keep his or her own gray matter nourished. Mahadevan has studied the patterns of crumpled paper, analyzed the way fabric folds and wrinkles, and stared at the feet of houseflies to determine what makes them stick, and then unstick, to ceilings and walls. The crumpled paper research has provided insight into the formation of mountain ranges, while the cloth studies have helped animators and Internet sales departments get virtual clothing to look more natural. The fly analysis may have applications for the glue industry. The Venus flytrap research included mathematicians, engineers, and biologists working with high-speed video cameras and computer models to track the near-instantaneous closing of the plant when food lands on its maw-like leaves. Mahadevan's team showed that the plant keeps those leaves stretched taut like a rubber band, and that the pent-up energy is released to capture the prey. The point of the experiment was to answer the question people ask about the world from the time they can talk: Why? ''The questions I ask are not important on a grand scale, but they're interesting because they're around us," Mahadevan told the Harvard University Gazette last summer. He said that what excites him ''are things so in your face that almost no one thinks about them." In an interview with the Globe last week, he noted that people often assume that because something is familiar, ''it is understood. But if you really probe, there are mysteries." Assumption is the enemy of curiosity and can cause people to misread each other, breeding prejudice -- or war. Assumption can poison a democracy with sleepy citizens who don't probe beyond slogans. Assumptions about nature can bring destruction to homes built precariously on mountainsides, or wash away lives by the thousands in a tsunami. Seeking an understanding of everything -- from a strange plant in a pot to the outermost dust in the cosmos -- is the zest of science, and the best way to meet the challenge of living. -------------------------------- Astronomers Find 'Hot Spot' on Saturn By JAYMES SONG Feb 4, 9:32 AM (ET) HONOLULU (AP) - Astronomers using a giant telescope atop a volcano have discovered a hot spot at the tip of Saturn's south pole. The infrared images captured by the Keck I telescope at the W.M. Keck Observatory atop Mauna Kea on the Big Island suggest a warm polar vortex - a large-scale weather pattern likened to a jet stream on Earth that occurs in the upper atmosphere. It's the first such hot vortex ever discovered in the solar system. The team of scientists say the images are the sharpest thermal views of Saturn ever taken from the ground. Their work will be a published in Friday's editions of the journal Science. This warm polar cap is believed to contain the highest temperatures on Saturn; the scientists did not give a temperature estimate. On Earth, the Arctic Polar Vortex is typically located over eastern North America in Canada and plunges cold arctic air to the northern Plains in the United States. Polar vortices are found on Earth, Jupiter, Mars and Venus, and are colder than their surroundings. The new images from the Keck Observatory show the first evidence of a polar vortex at much warmer temperatures. "Saturn's is the first hot polar vortex that we've seen because it's been sitting in the sunlight for about 18 years," said Glenn S. Orton, a scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif., and lead author. Saturn, which takes many earth years to orbit the sun, just had its summer solstice in 2002. "If the increased southern temperatures are solely the result of seasonality, then the temperature should increase gradually with increasing latitude, but it doesn't," Orton said. "We see that the temperature increases abruptly by several degrees near 70 degrees south and again at 87 degrees south. "A really hot thing within a couple degrees of the pole is something I don't understand at all," he said. Scientists may learn more from the data coming from the infrared spectrometer on the Cassini spacecraft currently orbiting Saturn, information that is expected to complement the Keck discovery, Orton said. --- On the Net: Keck Observatory: http://www.keckobservatory.org Jet Propulsion Laboratory's Saturn page: http://saturn.jpl.nasa.gov http://www2.keck.hawaii.edu/news/science/saturn/saturn2004a.jpg public_html/random-stuff/images/ ------------------------------------------------------------ http://www.digitalsundial.com/patent.html make a "digital" clock that displays the correct hour (and minute) through shadows cast ----------------------------- reversible stokes flow of (a heavy MW) dye in glycerin/oil/other-viscous-fluid helical motion and its reverse dye blob w/a dancing needle/paddle that's computer controlled 3 DOF - up/down, around, in/out (from center) animate the barber of seville? --------------------------------------- photo p80 of april 2005 scientific american book of photos of microscopic phenomena by that MIT visitor who lectured to the freshman interest group headed by dan -------------------------------- geodynamo - april 2005 sci am pp 50--57 fellow who gave a talk at TICAM ------------------------------- record bird calls sonograms in the range from 1 kHz to 100 kHz (or more) "the singing life of birds" by kroodsma (rev in may 2005 sci am) -------------------------------- sonoluminescence refs in my paper for brenner and others bubbles in H2SO4 confirm blackbody radiation? nature, march 3, 2005 ------------------------ (from june? 2005 sci am) Entomology Descent of the Ants Rather than falling haphazardly, 25 species of arboreal ants in Panama, Costa Rica, and Peru can glide back to their home trees --- the first known instance of wingless insects guiding their fall. White nail polish on the ants' rear legs and high-speed video revealed that after being dropped from 30 meters up, ants can swivel quickly to glide backward to a tree. They can make 180-degree turns in midair that ppear to involve abdominal undulations, airfoil-like flattened hind legs, and flattened heads with flanges that can act as rudders. Eighty-five percent of canopy ant (*Cephalotes atratus*) workers returned to their home tree after falling, frequently crawling back to the branch from which they started within 10 minutes. Evidence suggests that the ants sometimes might purposely drop off trees to avoid predators. The report landed in the February 10 *Nature*. ------------------- (from june 2005 sci am) Physics No-Splash Liquid The key for anyone wanting to make a big splash is pressure --- of the atmospheric kind, that is. Normally, when a liquid droplet hits a surface, it spreads into an undulating puddle that rips apart into a splatter. Seeking to control splashing, University of Chicago physicists released alcohol drops in a vacuum chamber onto a smooth, dry glass plate and recorded the results with a camera shooting 47,000 frames per second. At roughly one-sixth normal atmospheric pressure, splashing completely disappeared; droplets just pancaked without visible undulations. The investigators suspect that fallen drops splatter because gas pressing on them destabilizes their outward spread. These findings, presented at the March meeting of the American Physical Society, could help control splashing in fuel combustion and in inkjet printing. ----------------------------- (from august 2005 sci am) Astronomy Cosmic CAT Scan Observing the early universe --- with 10,000 TV antennas By W. Wayt Gibbs In the beginning, the universe was a void full of energy but without form. And so it remained for many millions of years --- exactly how long is still a major mystery of cosmology --- until the first stars condensed from the fog of matter and lit up with a blue nuclear glow. Telescopes are just like time machines: the farther out in space they look, the further back into the past they peer. But even the best optical telescopes cannot make out what the universe was like at an age of less than one billion years. Before that time, a haze of neutral hydrogen gas shrouded these first beacons in the infant cosmos. A new radio observatory under construction on the high plateau of Ulastai in remote western China may soon yield images of this formative epoch, however --- and for a bargain price, too, because the sprawling instrument is built almost entirely from parts that one could buy at RadioShack. Even though it will cost just $3 million, the Primeval Structure Telescope (PaST) is one of China's largest investments so far in experimental astronomy. The project was launched in 2003 by Xiang-Ping Wu of the Chinese Academy of Sciences in Beijing, Jeffrey B. Peterson of Carnegie Mellon University in Pittsburgh, and Ue-Li Pen of the Canadian Institute for Theoretical Astrophysics in Toronto. Though formally a telescope, PaST is better thought of as an experiment. "We'll get enough data from it to answer our principal questions within a couple weeks of turning it on" next year, Peterson says. (Analyzing those data may take years, however.) That is because the instrument is essentially a giant, incredibly sensitive television receiver. PaST will combine radio signals picked up by 10,000 high-gain antennas arranged in lines up to three kilometers long. The log-periodic antennas, similar to those sold by the millions for rooftops, cost just $20 each. Household coaxial cable splitters, installed backwards, combine the signals from multiple antennas and feed them into a bank of 320 ordinary Pentium PCs, running free Linux software. The computers merge the data to produce a high-resolution picture of a 10-degree patch of sky centered near the North Star. Actually "picture" is not the right word, because PaST will record thousands of simultaneous signals within a broad swath of the VHF spectrum. The scientists are writing software to sift out uninteresting signals --- such as those from television stations, meteors and black holes at the centers of distant galaxies --- to reveal a kind of three-dimensional CAT scan of the early universe that theorists predict lies buried within the noise. As the first stars flickered on, their ultraviolet light excited neutral hydrogen atoms around them, causing the gas to emit a faint radio signal at 1,420 megahertz. As the starshine intensified, it eventually stripped electrons from the hydrogens, ionizing the atoms. But over time the expansion of the universe stretched the ancient radio waves, lowering their frequencies by an amount proportional to their age. Astronomers can thus see a particular moment in time and location in space by "tuning" their receiver to the appropriate frequency. "It's a bit like archaeology," says Abraham Loeb of the Harvard-Smithsonian Center for Astrophysics. "We can slice the universe and see more and more ancient layers as we go deeper." Astronomers expect that PaST will reveal a uniform haze of bright neutral hydrogen at about 200 million years after the big bang that became increasingly punctuated by bubbles of ionized --- and thus dark --- hydrogen surrounding the first stars. Simulations suggest that these shells then connected, like the voids in a Swiss cheese, to form tunnels. The neutral hydrogen fog gradually dissipated into stray wisps and vanished forever within the first billion years, leaving us with the transparent space we see today. This story will remain fuzzy until PaST or a competing observatory delivers more clarity. Let there be light. Race Against the PaST The Primeval Structure Telescope (PaST) faces competition from two higher-budget, higher-tech projects. "It's sort of a race right now," says Abraham Loeb, a cosmologist at the Harvard-Smithsonian Center for Astrophysics. "It's not clear who will win. Each experiment has advantages and disadvantages." * LOFAR project: 15,000 antennas in the Netherlands; pilot installation of 100 antennas now in place. Cost: At least $65 million to date. Cons: Noisy radio environment. * Mileura Widefield Array (WLA): 8,000 antennas in the Austalian outback. Cost: $10 million. Cons: proposed to, but not yet approved by, the US National Science Foundation. smoke powder 2:3 sugar to saltpeter heat on low flame to plasticize nitrogen triiodide napalm: wax, soap, eggwhite/(lye,salt,sugar,etc) w/gasoline,kerosene,etc get a piece of paper trace a nickel on the paper cut out the hole you traced (fold the paper with folds passing through the center of the circle --- halves, quarters, whatever --- cut the circle out, and unfold the paper) get a quarter through the hole without ripping the paper tie a rope around your ankles turn your pants inside out (why does the rope make this difficult?) compute the brightness of earth from mars (and vice versa) some assumptions to make the calculation easier: no atmosphere (so no daylight to contend with) spherical planets circular, coplanar, concentric orbits diffuse (uniform) not specular reflection observer where-ever desired on the planet (point-like planets) "far" from the sun (point-like planets) others? what is the importance of each of the assumptions? illustration of what you "see" when observing stars in a line put a source, some intervening gas, and the observer incandescent source on or off vacuum, cold gas, "warm" gas, hot gas eight possibilites; what does the observer see in each case? (what spectrum?) SIAM NEWS - March 1, 2005 Sara Robinson, "Can Mathematical Tools Illuminate Artistic Style?" using image analysis to detect impostor bruegel drawings -------------------------------- Spotlight on the dynamical systems community In Santiago, Chile, for the sixth Americas Conference on Differential Equations and Nonlinear Analysis (January 10-21), SIAM president Martin Golubitsky took time out for an interview with Hinke Osinga, section editor-in-chief of DSWeb Magazine. When the widely ranging conversation inevitably turned to SIAM Journal on Applied Dynamical Systems---of which Golubitsky is the founding editor-in-chief---he recalled the journal's startup, and the decision to make it electronic only. "It just had to be an electronic journal," he said; "how else can you have free color and animations!" The emphasis on visualization could hardly have had a more receptive listener: Osinga has been known since May 2003, in unexpectedly wide circles, for the unusual and strikingly beautiful illustration she brought to her talk at the sixth SIAM Conference on Applications of Dynamical Systems. In the mini- symposium talk, "Manifolds in the Lorenz System," she presented her work with Bernd Krauskopf on computing invariant manifolds. The now-famous illustration was a crocheted version of the Lorenz manifold produced by the algorithm described in the talk. "Famous" is not an exaggeration: As word about the crocheted manifold got out, helped along by a cover article in The Mathematical Intelligencer (Fall 2004), the mainstream media showed remarkable enthusiasm for the story. Osinga (a crocheter from the age of 7) and Krauskopf, both of the University of Bristol, were featured with their crocheted creation in several newspapers; they were also in-terviewed on radio, and even appeared on UK and Russian national television news. The highlight was their appearance on Channel 4 News, December 17, 2004, in a live interview of almost four minutes with presenter Jon Snow. ("So," he quipped, "where's the butterfly?") In their article, Osinga and Krauskopf published the crochet and mounting instructions that would allow anyone adept enough with a crochet hook and persistent enough to complete the 25,511 stitches to duplicate their feat. Curious about the mathematics involved, and the extent of the connection between the mathematics and the crocheted piece, SIAM News got in touch with Osinga and soon received generous replies to a set of questions (see From Computed to Crocheted Mesh). Meanwhile, Osinga was actively working on other projects for the dynamical systems community, including the article about Golubitsky. Posted to DSWeb Magazine (January 2005), the article is reproduced almost in its entirety in this issue of SIAM News. Osinga is also the editor-in-chief of DSWeb, the portal of the SIAM Activity Group on Dynamical Systems and the home of the Magazine; readers are encouraged to take a look: http://www.dynamicalsystems.org/. A final note: As SIAM president, in addition to the activities he mentioned to Osinga, Golubitsky intends to communicate with the SIAM membership via an occasional column in SIAM News. In fact, he had planned to begin with this issue. A phone call to remind him of the deadline found him hard at work with his long-time collaborator Ian Stewart, in town (Houston) to attend "Coupled 60," a conference on the dynamics, classification, and applications of coupled systems held as part of the University of Houston dynamics group's Focused Research Grant from the National Science Foundation. The name "Coupled 60," Golubitsky explained, "arose when we looked over the list of conference participants and realized that five of us would be turning 60 this year." In addition to Golubitsky and Stewart, the group includes John Guckenheimer (SIAM president in 1997- 98), Philip Holmes, and Michael Field. Over the years, the five have had substantial interaction in the course of separate, but intertwined research careers. All, Golubitsky said, began in catastrophe theory (singularity theory), and coupled systems that have structure are a current theme for all. -- From Computed to Crocheted Mesh March 1, 2005 Hinke Osinga and Bernd Krauskopf of the University of Bristol sent the following responses to questions from SIAM News about their crocheted Lorenz manifold (shown at right, photographed against a white background). (see article for photos) -------------------------------- A Bolt out of the Blue New research shows that lightning is a surprisingly complex and mystifying phenomenon By Joseph R. Dwyer Lightning is a particularly unsettling product of bad weather. It causes more deaths and injuries in the U.S. than either hurricanes or tornadoes do, and it strikes without warning, sometimes with nothing but blue sky overhead. In central Florida, where I live, thunderstorms are a daily occurrence during the summer, and so, ironically, people in the Sunshine State often spend their afternoons indoors to avoid the risk of death from the sky. Worldwide, lightning flashes about four million times a day, and bolts have even been observed on other planets. Yet despite its familiarity, we still do not know what causes lightning. It is a misconception that Benjamin Franklin solved the puzzle when he conducted his famous kite experiment in 1752. Although Franklin demonstrated that lightning is an electrical phenomenon, scientists to this day are struggling to understand how thunderstorms generate their charge and how lightning occurs. Some physicists have hypothesized that lightning may actually have an extraterrestrial connection, with cosmic rays--high-energy particles bombarding the earth from space--triggering cascades of speedy electrons in the atmosphere. Researchers have recently discovered a new avenue for studying lightning: examining the x-rays emitted as lightning streaks from the clouds to the ground. In the past few years, our team has measured the x-rays produced by both natural lightning and man-made bolts created by launching rockets during thunderstorms. The results suggest that lightning may carve its jagged, conductive channels by sending out blasts of high-speed electrons. But how lightning manages to accelerate these electrons is extremely perplexing. To solve the mystery, we are now building an array of x-ray detectors at a site in Florida. Stranger than Sparks In some ways, lightning resembles a big spark. Consider the conventional spark, the kind you get when you touch a doorknob after walking across a carpet. When you traverse the carpet, your shoes rub off electrons and you accumulate an electrical charge, which produces an electric field between you and other objects in the room. For small fields, air is a good insulator--electrons attach to oxygen atoms faster than they are knocked loose by collisions--and electric current cannot flow in any appreciable amount. As your finger approaches the knob, however, the electric field becomes locally enhanced. If it reaches a critical value of about three million volts per meter, called the breakdown field, the air becomes a conductor and a discharge occurs: current bridges the gap. The electrification of thunderstorms shares some similarities with the carpet example. Inside thunderclouds, the role of the shoes on the carpet is most likely played by soft hail--snow pellets--falling through ice crystals and water droplets. (The exact mechanisms are still under debate.) When these particles bump into one another, they can rub off electrons and become charged. The positive and negative charges are then separated by updrafts and gravity, producing the electric field. But if we try to press the doorknob analogy any further, we run into a big problem: decades of balloon, aircraft and rocket measurements made directly inside the clouds rarely find fields above about 200,000 volts per meter, which is much too low to cause air to break down like it does when we touch a doorknob. Until recently, scientists had focused on two explanations to solve this conundrum. First, it is possible that stronger electric fields do exist inside thunderstorms but only in relatively small volumes, making them difficult to measure. Although such a scenario cannot be ruled out observationally, it is not altogether satisfying, because we are merely replacing One problem with another: How do clouds produce strong electric fields in such small volumes? The second explanation comes from experiments showing that the electric field needed to produce a discharge is reduced substantially when raindrops or ice particles are present in the air, as they are inside thunderstorms. Unfortunately, the addition of rain or ice alleviates only some of the discrepancy; the fields in thunderstorms still appear to be too weak to generate a conventional discharge. Scientists are also uncertain about how lightning propagates many kilometers through the air. The process begins with the formation of a leader, a hot channel that can ionize the air and transport charge over long distances (see box on opposite page). Interestingly, the leader does not travel to the ground in a continuous fashion but instead moves along in a series of discrete steps. Exactly how all this occurs, however, is somewhat mysterious. Efforts to model these processes have not been entirely successful. These difficulties have led many researchers in the field, including me, to wonder if we have missed something important. For example, perhaps viewing lightning as an entirely conventional discharge, like a spark to a doorknob, is not correct. It turns out that another, more unusual kind of discharge exists: runaway breakdown. In a conventional discharge, all the electrons move relatively slowly because they are hampered by their constant collisions with air molecule. The collisions create an effective drag force that is similar to what you feel when you stick your hand out a car window: as the car goes faster the drag force increases, and as the car slows down it decreases. But if the electron velocities are high enough--at least six million meters per second, or about 2 percent of the speed of light--the drag force actually decreases the faster the electrons go (see illustration on page 69). If a strong electric field accelerates a high-speed electron, the drag force becomes smaller, which allows the electron to move even faster, thereby reducing the drag force further, and so on. Such runaway electrons can accelerate to nearly the speed of light, gaining enormous amounts of energy and producing the discharge called runaway breakdown. This process, though, requires a seed population of electrons with high initial energies. In 1925 Scottish physicist C.T.R. Wilson first suggested that the decay of radioactive isotopes or the collisions of cosmic-ray particles with air molecules could generate energetic electrons that would run away in the electric fields inside thunderclouds. Wilson's model, however, predicted that radioactive decay and cosmic-ray collisions would produce too few runaway electrons to cause lightning. In 1961 Alexander V. Gurevich of the Lebedev Institute of Physics in Moscow hypothesized another mechanism for making runaway electrons. Gurevich showed that in very strong electric fields, large numbers of runaway electrons could be produced by accelerating them directly out of the ubiquitous population of low-energy free electrons, thereby sidestepping Wilson's problem of a lack of energetic seed electrons. To generate such runaway electrons, Gurevich used a brute-force method in which the electric field is so incredibly strong that some of the low-energy electrons are quickly accelerated up and over the energy threshold, allowing them to run away. The difficulty with this mechanism is that it requires an electric field about 10 times larger than the conventional breakdown field, which in turn is much larger than the fields observed in thunderstorms. In short, physicists seemed to be heading in the wrong direction. Finally, in 1992, a new idea emerged that has shown promise for explaining what happens inside thunderstorms and how lightning occurs. Gurevich, along with Gennady M. Milikh of the University of Maryland and Robert RousselDupré of Los Alamos National Laboratory, proposed the Relativistic Runaway Electron Avalanche (RREA) model. According to this scenario, the runaway electrons themselves generate more energetic seed electrons by bumping forcefully into air molecules and knocking off other high-energy electrons. These knocked-off electrons then run away and collide with more air molecules, producing still more energetic seed electrons, and so on. The result is a large avalanche of high-energy electrons that grows exponentially with time and distance. Because this process can be initiated by as few as one energetic seed electron, the steady background of cosmic-ray collisions and radioactive decays would be sufficient to trigger an avalanche of runaway electrons. And as long as the avalanche remains in a region with a strong electric field, it will continue to grow almost indefinitely, resulting in a runaway breakdown. Furthermore, unlike Gurevich's older hypothesis, this new model of runaway breakdown requires an electric field only one tenth as large as that needed for a conventional breakdown in dry air. At thunderstorm altitudes, where the air density is lower than at sea level, the electric field needed for this type of runaway breakdown is about 150,000 volts per meter--comfortably within the range of values measured inside thunderstorms. Indeed, it is probably not a coincidence that the maximum observed electric field inside thunderclouds and the field needed for runaway breakdown are about the same; my calculations have shown that runaway breakdown would efficiently discharge the electric field if it were to rise much higher. In a normal discharge, all the electrons have low energies and travel fairly slowly, so the electromagnetic radiation emitted by the spark extends only as high as the ultraviolet range. In a runaway breakdown, though, the fast-moving electrons ionize large numbers of air molecules and produce high-energy x-rays and gamma rays. (The phenomenon is known as bremsstrahlung, German for "braking radiation.") Consequently, one way to test for runaway breakdown is to search for x-rays. If Superman Saw Lightning Motivated first by Wilson's hypotheses and later by Gurevich's work, scientists have attempted to Observe x-rays from thunderstorms and lightning since the 1930s. Such measurements are very challenging to make and until recently have produced mostly ambiguous results. One difficulty is that x-rays do not travel very far through the atmosphere and are usually absorbed within a few hundred meters of the source. Another problem is that thunderstorms are electromagnetically noisy environments. Lightning, in particular, emits large amounts of radio-frequency noise, causing the familiar crackle on AM radios many kilometers away. Detecting x-rays involves recording small electrical signals; trying to make such measurements near lightning is like trying to hear a conversation in a raucous restaurant. Because it can be hard to distinguish real electrical signals produced by x-rays from spurious ones produced by radiofrequency emissions, many of the early results were not readily accepted. The situation got more interesting in the 1980s, when George K. Parks, Michael P. McCarthy and their collaborators at the University of Washington made aircraft observations within thunderstorms. Later, Kenneth B. Eack, now at the New Mexico Institute of Mining and Technology (NMT), and his coworkers made a series of balloon soundings inside thunderclouds. These observations provided tantalizing hints that thunderstorms occasionally produce large bursts of x-rays. The source of these x-rays could not be pinpointed, but the radiation seemed to be associated with the enhanced electric fields inside the clouds. Interestingly, the x-ray emission sometimes began right before lightning was observed and stopped once the lightning occurred, perhaps because lightning shorted out the electric fields needed to produce runaway breakdown. Researchers know of no mechanism besides runaway breakdown that could produce such large quantities of x-rays in our atmosphere. Other phenomena associated with lightning cannot be responsible for the emissions; although lightning can heat the air up to 30,000 degrees Celsius--five times as hot as the sun's surface--virtually no x-rays are produced at this temperature. Scientists finally found a direct link between x-rays and lightning in 2001, when Charles B. Moore and his co-workers at NMT reported observing energetic radiation, presumably x-rays, from several natural lightning strikes on top of a tall mountain. Unlike the earlier aircraft and balloon observations, this energetic radiation seemed to be produced by the lightning itself and not by the large-scale electric fields inside the thundercloud. Furthermore, the emissions appeared to occur during the first phase of lightning, the movement of the leader from the cloud to the ground. This observation was something entirely new. Here is where I entered the picture. As a physicist, I have always been interested in how x-rays and gamma rays are produced. Although such radiation is common in space, where the vacuum allows energetic particles to travel unimpeded, it is much rarer on the earth. Consequently, I became fascinated by Gurevich, Milikh and Roussel-Dupré's runaway breakdown model, which suggested that the same kind of x-rays produced by events such as solar flares could also be made by thunderstorms and lightning. I decided to see for myself if these purported x-rays really did exist by investigating the frequent thunderstorms in my own backyard. In 2002, with funding from the National Science Foundation, my group at the Florida Institute of Technology, in collaboration with Martin A. Uman and his team at the University of Florida, began a systematic campaign to search for x-ray emissions from lightning. To reduce the problems of spurious signals, we placed sensitive x-ray detectors inside heavy aluminum boxes designed to keep out moisture, light and radio-frequency noise. We set up our instruments at the International Center for Lightning Research and Testing (ICLRT) in Camp Blanding, Fla. Operated by the University of Florida and Florida Tech, the ICLRT is equipped to measure, among other things, the electric and magnetic fields and optical emissions associated with lightning. Moreover, the facility is capable of artificially triggering lightning from natural thunderstorms using small rockets. When a thunderstorm is above the ICLRT and the electric field on the ground reaches several thousand volts per meter, researchers launch a one-meter-long rocket from a wooden tower. The rocket uncoils a spool of thin Kevlar-coated copper wire, one end of which remains attached to the ground. As the rocket rises as high as 700 meters, the vertical grounded wire enhances the electric field at the rocket's tip, resulting in an upward-propagating leader that eventually snakes its way into the thundercloud. Electric current rising from the ground into the leader quickly vaporizes the wire. About half the launches trigger lightning from the clouds above, and the bolts usually strike the rocket launcher. Both natural and man-made lightning flashes are usually composed of several strokes. For triggered lightning, each stroke starts as a downward-propagating column of charge called a dart leader that, near the ground, more or less follows the path left by the rocket and triggering wire. The dart leader brings down negative charge from the cloud and ionizes the channel as it moves. Once the dart leader connects to the ground, a short circuit is created and a large pulse of current, called the return stroke, flows through the channel. The current in the return stroke quickly heats the channel, causing the visible light that we see, and the subsequent rapid expansion of the hot air causes the thunder that we hear. After the return stroke, another dart leader can follow, whereupon the entire process repeats. The quick succession of strokes is what causes the lightning channel to flicker. In natural lightning the role of the rocket is played by a stepped leader, which forges the ionized path, extending in jagged steps from the cloud to the ground. The subsequent strokes of natural lightning, however, are initiated by a dart leader, making them very similar to the strokes of triggered lightning. The advantage of studying the latter is that the exact time and place of the lightning strike can be controlled. What is more, the experiment can be repeated over and over; dozens of lightning flashes are triggered at the ICLRT every summer. To be honest, given the long history of negative and ambiguous x-ray results, I was not really expecting to measure any x-rays from lightning when we first set up our instruments at the ICLRT. For this reason, after we made our first triggered-lightning measurements I did not get around to looking at our data for more than a week. When I finally sat down with my graduate student, Maher Al-Dayeh, and plotted the data from the x-ray detectors, I nearly fell off my chair. To my surprise--and to the surprise of just about everyone else--we discovered that triggered lightning produces lots and lots of x-rays nearly every time. Indeed, the x-ray flashes were so intense that our instruments were temporarily blinded by the radiation. Subsequent experiments over the next year showed that the x-ray emission is produced by the lightning dart leaders, possibly with some contribution from the beginning of the return strokes. The energies of the x-rays extend to around 250,000 electron volts, or about twice the energy of a chest x-ray. Furthermore, the x-ray emission is not produced continuously but happens in rapid bursts a millionth of a second apart. If humans had x-ray vision like Superman, lightning would look quite different from what we are used to: as the lightning leader propagated downward, we would see a rapid series of bright flashes descending from the clouds. The flashes would strengthen as they approached the ground, ending with a very intense burst at the instant the return stroke began. Although the pulse of current that would follow would be brilliant in visible light, it would look black in x-rays. The observation of x-rays from lightning indicates that some form of runaway breakdown must be involved to accelerate the electrons enough to produce bremsstrahlung radiation. But it turns out that our measurements do not square well with the RREA model developed by Gurevich, Milikh and RousselDupré. The x-rays we observed had much lower energies than those predicted by the avalanche model, and the intensity of the bursts was much higher than expected. In fact, the results suggest that the electric fields produced by lightning leaders are much, much larger than what was previously believed possible. Ironically, our experiments so far indicate that the mechanism at work in lightning leaders is more akin to the old model of runaway breakdown proposed by Gurevich in 1961--the one requiring such a large electric field that it was initially discounted. Exactly how lightning can generate such large electric fields remains a mystery, but further x-ray observations should provide clues. Since the initial discovery of x-rays from triggered lightning, we have observed several natural lightning strikes at the ICLRT as well. These data showed beautiful x-ray emissions from the stepped-leader phase, confirming the earlier NMT measurements. Furthermore, the x-rays arrived in fast bursts at exactly the same times when the leader stepped downward. This result demonstrates that runaway breakdown is involved in the stepping process, determining where the lightning will go and how it branches. A similar mechanism is also at work during the dart-leader phases of the subsequent strokes. In short, the x-ray emissions from natural lightning are very similar to those from triggered lightning. It is becoming clear that runaway breakdown is a common phenomenon in our atmosphere. Despite the fact that air molecules hinder the acceleration of fast electrons, we see evidence for runaway breakdown even near the ground, where the air is densest. (Most of the x-rays we observed came from the bottom 100 meters or so of the lightning channel.) Thus, runaway breakdown may happen even more frequently at thunderstorm altitudes. Back in the Thunderstorm What about lightning initiation within thunderclouds? In the past few years, researchers have constructed promising models that show how the particle showers created by cosmic-ray impacts could work together with runaway breakdown to make lightning. Because big avalanches of runaway electrons can be produced by just one energetic seed electron, the discharge triggered by a large cosmic-ray shower-which involves millions of energetic seed particles arriving simultaneously--must be truly enormous. Such a large discharge could generate a localized enhancement of the electric field at the front of the avalanche because of the great increase in the electrical charge there. This enhancement may act like a finger near a doorknob, briefly raising the electric field to the point where a conventional electrical breakdown can take place. A fascinating piece of evidence supporting runaway breakdown inside thunderclouds came from our experiments at the ICLRT last summer. During the final rocket launch of the season, we fortuitously caught a huge burst of very high energy radiation--gamma rays, not x-rays--using three detectors placed 650 meters from the lightning channel. The energies of the individual gamma-ray photons extended to more than 10 million electron volts, or about 40 times higher than the energies of the x-rays that we had previously observed from lightning leaders. Anyone who pictures scientists as calm and reserved should have seen us when the data from that gamma-ray flash appeared on our computer. One might have thought that our favorite team had just scored the winning touchdown at the Super Bowl. Based on our measurements of the lightning channel current, the electric fields and the properties of the gamma rays, we have inferred that the source of the emission was probably many kilometers up in the thundercloud. We did not expect to see gamma rays from this altitude because the atmosphere absorbs such radiation, but apparently the intensity at the source was so great that some photons were able to make it to the ground. This finding suggests that massive runaway breakdown may have happened within the thundercloud in a process related to the initiation of the triggered lightning. Our observations demonstrate that it is possible to study this phenomenon on the ground, which is experimentally much simpler than lofting detectors onto aircraft or balloons. Furthermore, scientists recently reported that the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) detected similar gamma-ray bursts associated with thunderstorms while orbiting 600 kilometers away! With additional funding from the National Science Foundation, we are now expanding the number of x-ray instruments at the ICLRT from five to more than 36, covering one square kilometer of the Camp Blanding site. This expansion should improve our ability to study natural lightning as well as triggered lightning and should increase the odds of detecting more gamma-ray bursts from the thunderclouds. The x-ray and gamma-ray emissions can serve as probes to help determine the electric fields in regions that are otherwise very difficult to measure. The results should allow us to better understand the breakdown processes that initiate lightning and facilitate its propagation. Using x-rays to study lightning is still new, and consequently, just about every time we conduct an experiment we discover something we did not know before. We have already learned that lightning is not just an ordinary spark like the kind you get when you touch a doorknob. It involves a more exotic type of discharge that produces runaway electrons and x-rays. Because x-rays allow us to look at lightning in a novel way, this research may help us finally solve the puzzle tackled by Benjamin Franklin two and a half centuries ago. Overview/The Nature of Lightning * Lightning has baffled physicists for decades because the electric fields inside thunderclouds do not appear to be strong enough to generate a conventional discharge of current. * New observations of x-rays from lightning bolts support the hypothesis that lightning somehow accelerates electrons to nearly the speed of light in a phenomenon called runaway breakdown. * Researchers are building an array of x-ray detectors in Florida to study the processes that initiate lightning and allow it to propagate. MORE TO EXPLORE The Electrical Nature of Storms. Donald R. MacGorman and W. David Rust. Oxford University Press, 1998. The Lightning Discharge. Martin A. Uman. Dover Publications, 2001. Energetic Radiation Produced during Rocket-Triggered Lightning. Joseph R. Dwyer et al. in Science, Vol. 299, pages 694-697; January 31, 2003. Lightning: Physics and Effects. Vladmir A. Rakov and Martin A. Uman. Cambridge University Press., 2003. GRAPH: RUNAWAY ELECTRONS blaze the trails for lightning bolts. Low-energy electrons, which move relatively slowly, lose more energy to drag--collisions with air molecules--than they gain from an electric field, so they slow down further. But because high-energy electrons lose less energy to drag, the electric field can accelerate them to nearly the speed of light. PHOTO (COLOR): NATURE'S X-RAY MACHINE: Recent studies show that lightning emits bursts of x-rays as it carves its jagged conductive channels through the atmosphere. The energies of the x-rays extend to 250,000 electron volts, or about twice the energy of a chest x-ray. PHOTO (BLACK & WHITE): TRIGGERED LIGHTNING is produced at the International Center for Lightning Research and Testing in Florida by launching a small rocket from a wooden tower during a thunderstorm. The rocket trails a wire that carries current from the ground, creating a path fro the lightning bolt. Nearby instruments measure the energy and intensity of the emitted x-rays. PHOTO (COLOR) PHOTO (COLOR) PHOTO (COLOR) ~~~~~~~~ By Joseph R. Dwyer JOSEPH R. DWYER is an associate professor of physics and space sciences at the Florida Institute of Technology. After receiving his Ph.D. in physics from the University of Chicago in 1994, he worked as a research scientist at Columbia University and the University of Maryland before moving to Florida in 2000. The author would like to acknowledge the contributions of H. Rassoul, V. Rakov, M. Al-Dayeh, J. Jerauld, L. Caraway, B. Wright, K. Rambo and D. Jordan to this research. -- diagram -- THE BRIEF LIFE OF LIGHTNING Some scientists believe that lightning may be triggered by cosmic rays, high-energy particles bombarding the earth from space. 1 A fast-moving proton from space collides with an air molecule (usually nitrogen or oxygen) in the upper atmosphere, producing a shower of high-energy particles. Proton Air molecule 2 Particles in the shower, including energetic electrons, hit air molecules in a thundercloud, ejecting other high-energy electrons. Accelerated by electric fields stretching between regions of negative and positive charge, the particles initiate an avalanche of runaway electrons, which generate gamma rays as they blast through the cloud. This runaway breakdown may serve as a catalyst for lightning. Region of negative charge High-energy see electron Runaway electron Region of positive charge Gamma rays Thundercloud 3 Once lightning is initiated, the electrons carve an ionized channel called the stepped leader. At each step, electrons accumulate at the leader\x{2019}s tip, creating an intense localized field that accelerates more runaway electrons. The particles collide with air molecules, producing bursts of x-rays. The process repeats until the stepped leader, which can diverge into branches reaches the ground. Collision with air molecule X-rays Stepped leader 4 Once the leader connects to the ground, a large pulse of current flows through the channel. The current heats the air up to 30,000 degrees Celsius, causing the flash of visible radiation called the return stroke Flow of electrons through ionized channel Visible radiation DIAGRAM: Brief Life of Lightning ------------------------------------------- Recreating an Ancient Death Ray By JOHN SCHWARTZ October 18, 2005 Did Archimedes really produce a death ray 2,200 years ago? According to Greek and Roman historians, he set Roman warships afire with a polished mirror that focused the sun\u2019s rays from afar during the siege of Syracuse. Last year the Discovery Channel program "MythBusters" declared the story a myth after failing to reproduce the feat. The program intrigued David Wallace, a professor at the Massachusetts Institute of Technology. When he presented the death ray as an offbeat project for his class in product development, he said, "only a small number thought it was technically possible." On Oct. 4 on the roof of M.I.T.\u2019s West Garage, the class set up 127 cheap one-squarefoot mirrors 100 feet from a wooden mockup of the side of a ship. Clouds dogged the experiment, but with just 10 minutes of clear sky, the "ship" burst into flames. "Flash ignition!" Dr. Wallace exulted on the Web site devoted to the experiment, web.mit.edu/2.009/www/lectures/10_ArchimedesResult.html. The results first appeared on the Web site boingboing.net. "We're not trying to assess whether Archimedes really did it or not," Dr. Wallace said. Instead, they have shown that "it's at least possible." Peter Rees, the executive producer of the TV program, applauded the work. "Here at 'MythBusters' we are always happy to be involved in any kind of quasi historical/scientific debate," he wrote in an e-mail message, "especially if we prompted it." Like Dr. Wallace, he said that the M.I.T. experiment did not prove that Archimedes actually created a death ray, or that it would have worked on actual ships in real-world conditions. ----------------------------------------------- berkeley problems in math 3rd ed 2004 $50 geometry by lang/murrow 2nd ed 6th printing unsolved problems in geometry croft, falconer, guy 2nd printing After the counting numbers, geometry is the oldest branch of mathematics and no doubt the first one that required abstract thinking. Even so, there is always a certain "concreteness" about it in the sense that diagrams can almost always be constructed. The range of problems that fall under the geometric umbrella is extremely wide and some even have practical uses. This book is a testament to the wide range of problems that are geometric in nature. One of my favorites is known as the "worm problem." To be more precise, the question is, "find the convex set of least area where any continuous curve of length one can be placed in it." This type of problem has ramifications in optimal packings, where a single type of container needs to be constructed for all possible ways an object can fold. Other problems such as tiling and dissection; packing and covering and combinatorial geometry are also covered. However, the best part of the book may be the extensive references. Every problem is followed by a list of references, so if you wish to take a crack at it, you will have little difficulty in locating the work done to the date of publication. This is one of those books that always seems to beckon me when it lies on my bookshelf. Every once in awhile I pull it off and browse through it, admiring the skill and breadth of mathematicians in their pursuit of truth. It should be in every academic library. geometry for the classroom clemens and clemens 1992 story of the infinity hotel ------------------------------- Explaining Ice: The Answers Are Slippery By KENNETH CHANG February 21, 2006 Tuesday Here is one question that probably won't cross the minds of Sasha Cohen, Irina Slutskaya and the other Olympic women figure skaters today, even if they fall: Why is ice slippery? But maybe it should. After all, ice is a solid, and trying to glide on thin metal blades across the surfaces of most solids -- concrete, wood, glass, to name a few -- results in ear-piercing sounds and ungraceful stumbles. Though the question may seem to be a simple one, physicists are still searching for a simple answer. The explanation once commonly dispensed in textbooks turns out to be wrong. And slipperiness is just one of the unanswered puzzles about ice. Besides the everyday ice that you slip on, there are about a dozen other forms, some of which experts suspect exist in the hot interior of Earth or on the surface of Pluto. Scientists expect to discover still more variations in the coming years. Ice, said Robert M. Rosenberg, an emeritus professor of chemistry at Lawrence University in Appleton, Wis., and a visiting scholar at Northwestern University, ''is a very mysterious solid.'' Dr. Rosenberg wrote an article looking at the slipperiness of ice in the December issue of Physics Today, because he kept coming across the wrong explanation for it, one that dates back more than a century. This explanation takes advantage of an unusual property of water: the solid form, ice, is less dense than the liquid form. That is why ice floats on water, while a cube of frozen alcohol -- which has a freezing temperature of minus 173 degrees Fahrenheit -- would plummet to the bottom of a glass of liquid alcohol. The lower density of ice also means that the melting temperature of ice can be lowered below the usual 32 degrees by squeezing on it. According to the frequently cited -- if incorrect -- explanation of why ice is slippery under an ice skate, the pressure exerted along the blade lowers the melting temperature of the top layer of ice, the ice melts and the blade glides on a thin layer of water that refreezes to ice as soon as the blade passes. ''People will still say that when you ask them,'' Dr. Rosenberg said. ''Textbooks are full of it.'' But the explanation fails, he said, because the pressure-melting effect is small. A 150-pound person standing on ice wearing a pair of ice skates exerts a pressure of only 50 pounds per square inch on the ice. (A typical blade edge, which is not razor sharp, is about one-eighth of an inch wide and about 12 inches long, yielding a surface area of 1.5 square inches each or 3 square inches for two blades.) That amount of pressure lowers the melting temperature only a small amount, from 32 degrees to 31.97 degrees. Yet ice skaters can easily slip and fall at temperatures much colder. The pressure-melting explanation also fails to explain why someone wearing flat-bottom shoes, with a much greater surface area that exerts even less pressure on the ice, can also slip on ice. Two alternative explanations have arisen to take the pressure argument's place. One, now more widely accepted, invokes friction: the rubbing of a skate blade or a shoe bottom over ice, according to this view, heats the ice and melts it, creating a slippery layer. The other, which emerged a decade ago, rests on the idea that perhaps the surface of ice is simply slippery. This argument holds that water molecules at the ice surface vibrate more, because there are no molecules above them to help hold them in place, and they thus remain an unfrozen liquid even at temperatures far below freezing. Scientists continue to debate whether friction or the liquid layer plays the more important role. Dr. Rosenberg, asked his opinion, chose a indecisive answer: ''I say there are two major reasons.'' The notion that ice has an intrinsic liquid layer is not a new concept. It was first proposed by the physicist Michael Faraday in 1850 after a simple experiment: he pressed two cubes of ice against each other, and they fused together. Faraday argued that the liquid layers froze solid when they were no longer at the surface. Because the layer is so thin, however, it was hard for scientists to see. In 1996, Gabor A. Somorjai, a scientist at Lawrence Berkeley Laboratory, bombarded the surface of ice with electrons and watched how they bounced off, producing a pattern that looked at least partially liquid at temperatures down to minus 235 degrees. A couple of years later, a team of German scientists bounced helium atoms off ice and found results that corroborated the Lawrence Berkeley findings. ''The water layer is absolutely intrinsic to ice,'' Dr. Somorjai said. The findings, he said, fit with a simple observation that suggests friction cannot be the one and only explanation of slipperiness. When a person stands on ice, he added, no heat is generated through friction, and yet ''ice is still slippery.'' But a colleague of Dr. Somorjai's at Lawrence Berkeley, Miquel Salmeron, while he does not dispute Dr. Somorjai's experiment, does dispute the importance of the intrinsic liquid layer to slipperiness. In 2002, Dr. Salmeron and colleagues performed an experiment. They dragged the tip of an atomic force microscope, resembling a tiny phonograph needle, across the surface of ice. ''We found the friction of ice to be very high,'' Dr. Salmeron said. That is, ice is not really that slippery, after all. Dr. Salmeron said that this finding indicates that while the top layer of ice may be liquid, it is too thin to contribute much to slipperiness except near the melting temperature. In his view, friction is the primary reason ice is slippery. (The microscope tip was so small that its friction melted only a tiny bit of water, which immediately refroze and therefore did not provide the usual lubrication, he said.) Dr. Salmeron concedes, however, that he cannot definitively prove that his view is the correct one. ''It's amazing,'' he said. ''We're in 2006, and we're still talking about this thing.'' Ice formed by water behaves even more strangely at lower temperatures and higher pressures. Water -- H2O -- seems to be a simple molecule: two hydrogen atoms connected to a central oxygen atom in a V-shape. In everyday ice, which scientists call Ice Ih, the water molecules line up in a hexagonal pattern; this is why snowflakes all have six-sided patterns. (The ''h'' stands for hexagonal. A variation called Ice Ic, found in ice crystals floating high up in the atmosphere, forms cubic crystals.) The crystal structure of the ice is fairly loose -- the reason that Ice Ih is less dense than liquid water -- and the bonds that the hydrogen atoms form between water molecules, called hydrogen bonds, are weaker than most atomic bonds. At higher pressures, the usual hexagonal structure breaks down, and the bonds rearrange themselves in more compact, denser crystal structures, neatly labeled with Roman numerals: Ice II, Ice III, Ice IV and so on. Scientists have also discovered several forms of ice in which the water molecules are arranged randomly, as in glass. At a pressure of about 30,000 pounds per square inch, Ice Ih turns into a different type of crystalline ice, Ice II. Ice II does not occur naturally on Earth. Even at the bottom of the thickest portions of the Antarctic ice cap, the weight of three miles of ice pushes down at only one-quarter of the pressure necessary to make Ice II. But planetary scientists expect that Ice II, and possibly some other variations, like Ice VI, exist inside icier bodies in the outer solar system, like the Jupiter moons Ganymede and Callisto. With pressure high enough, the temperature need not even be cold for ice to form. Several Februaries ago, Alexandra Navrotsky, a professor of chemistry, materials science and geology at the University of California, Davis, was visiting Northwestern. She was sitting in office of Craig R. Bina, a geophysicist, and looking out over frozen Lake Michigan. ''Ice might have been on our minds,'' she recalled. The scientists started considering what happens to tectonic plates after they are pushed back down into Earth's interior. At about 100 miles down, the temperature of these descending plates is 300 to 400 degrees -- well above the boiling point of water at the surface -- but cool compared with that of surrounding rocks. The pressure of 700,000 pounds per square inch at this depth, Dr. Bina and Dr. Navrotsky calculated, could be great enough to transform any water that was there into a solid phase known as Ice VII. No one knows whether ice can be found inside Earth, because no one has yet figured out a way to look 100 miles underground. Just as salt melts ice at the surface, other molecules mixing with the water could impede the freezing that Dr. Bina and Dr. Navrotsky have predicted. Ice also changes form with dropping temperatures. In hexagonal ice, the usual form, the oxygen atoms are fixed in position, but the hydrogen bonds between water molecules are continually breaking and reattaching, tens of thousands of times a second. At temperatures cold enough -- below minus 330 degrees -- the hydrogen bonds freeze as well, and normal ice starts changing into Ice XI. William B. McKinnon, a professor of earth and planetary sciences at Washington University in St. Louis, said that astronomers were probably already looking at Ice XI on the surface of Pluto and on the moons of Neptune and Uranus. But instruments currently are not sensitive enough to distinguish the slight differences among the ices. The most recently discovered form of ice, Ice XII, was found just a decade ago, although hints of it had been seen years earlier. John L. Finney of University College London, one of the discoverers of Ice XII, said that trying to understand all the different forms of ice was important for an understanding of how the water molecule works, and that was important in understanding how water interacts with all the biological molecules in living organisms. ''It gives you a very stringent test for our understanding of the water molecule itself,'' he said. And could there be an Ice XIII? ''Yes,'' Dr. Finney said. ''Call me in a month.'' But scientists have given no word on whether any of these other types of ice are slippery enough to land a triple axel. http://images.google.com/images?hl=en&lr=&safe=off&q=+site:www.physics.utoronto.ca+ice http://www.physics.utoronto.ca/~smorris/edl/icespikes/icespikes.html ----------------------- [6] Grzybowski B., Winkelman A., Wiles J., Brumer Y. and Whitesides G., Elec- trostatic self-assembly of macroscopic crystal using contact electrification, Na- ture 2003 vol. 2 pp. 241-245 [7] Nadal F., Argoul F., Hanusse P. and Pouligny B., Electrically induced inter- actions between colloidal particles in the vicinity of a conducting plane, Phys. Rev. E., vol. 65, 061409 1-8 see nikolay's proposal for other refs ------------------------------------- Stonehenge in the City By MICHAEL POLLAK, NYT Published: May 21, 2006 Q. I've heard about a "Manhattan solstice," when the sun supposedly lines up along the streets. Is it for real? When does it happen? A. Here's the lowdown on the sundown, courtesy of Neil deGrasse Tyson, director of the Hayden Planetarium at the American Museum of Natural History. On May 28 and on July 13, the sun will fully illuminate every Manhattan cross street (not the curved or angled ones) on the street grid during the last 15 minutes of daylight, and it will set on each street's center line. The sight is breathtaking. This is a special photo opportunity, with parts of Manhattan's canyons getting illumination they normally don't get. If the Manhattan street grid ran north-south and east-west, the alignment days would be the spring and fall equinoxes, the two days when the sun rises due east and sets due west. But the Manhattan grid is angled 30 degrees east from geographic north, shifting the days. There are two corresponding mornings of sunrise right on the center lines of the Manhattan grid, Dr. Tyson wrote in an e-mail message: Dec. 5, 2006, and Jan. 8, 2007. Those four solstice days will shift no more than a day over four years as a result of leap days, Dr. Tyson wrote. But the shift is so small that if you went out only on these dates, you would see the effect just fine. "In fact the effect is good for a day on either side of the advertised days, typically offering a range of weather choices for the avid viewer," he wrote. As for the sunset next Sunday and on July 13, Dr. Tyson wrote, the sun will line up on the center lines just as its falls halfway below the horizon. The official sunset, when "the sun's last smidgen sets below the horizon," lines up on slightly different days, but this one makes for a nicer photo. ------------------------------------- Roger Moore: Physics. Roger Moore, aslo known to us as "Mini Moore" was for a period of time, my physics teacher while I was studying for A-Levels. He was a diminuvtive guy, who was struggling to deal with the up-and-coming breed of youngsters who showed little or No respect for thier elders. We, however were a bunch of 18year old guys who had a serious soft-spot for this guy. He was kind, gentle, and prone to making the best toys known to man. At one period in time, for some reaon were were talkign about stable structures, and honeycomb came into the conversation. Mini reconed he could demonstrate this.... He made a plastecene dam around the glass on the Old Overhead projector, and filled it with soapy water. Armed with a length of hose, he blew bubbles, and created a hone-comb of bubbles. One problem... His breathing was not constant. bubbles were different sizes. 5 minutes later, he'd made a glass nozzle and was usign the lab's gas supply to blow tiny bubbles. these were projected neatly onto the wall, albeit a bit feint. He then wanted bigger bubbles.... so hit upon a plan to destroy the others.. lighted splint. Neat. The lesson went on with Mini finding excuses to burn the bubbles... and we inqured as to whether he'd given thought to blowing BIG bubbles.... One week later, we turned up to a lesson, and mini was wearing a grin that threatened to separate the top of his head from the rest of his body... "Good morning gentlemen, Inspired by your question last week, I've made soemthing..." he motioned towards the corner of the lab where a rather simple rig stood. He then proceeded to blow foot-ball sized bubbles with propane... The bubbles were a bit too heavy to go floating, but that didn't matter, he poked them with a lghted splint, and they turned into one of the most beautiful things I've seen. A gentle orange fire-ball that floated up and hit the ceiling, and expanding in ring of fire that rolled out accross the ceiling until it ran out of gas. Other such experiments were more complex, I remeber him playing with large coils, capacitors and lumps of aluminum, and demonstrating the theory behind the Iraqi super-guns suspected electro-magnetic propulsion system. He embedded a 1 meter length of aluminium scaffolding pole in the lab's wall... He simply grinned a sheepish grin and said "oops". Mini was an inspirational figure for us, a nice guy, and a great teacher. If anyone reading this lives in or near the sleepy Cumbrian town of Sedbergh, and occasionally bumps into the legend of physics teacher, probably now around 70 years old, with comicly big ears, Tell him we remeber him, and that without doubt, he was the best teacher we ever had. ----------------------------------------------------------- from http://chemistry.about.com/od/demonstrationsexperiments/ss/liquidmagnet.htm How to Make Liquid Magnets From Anne Marie Helmenstine, Ph.D., How to Make Liquid Magnets - Introduction A liquid magnet or ferrofluid is a colloidal mixture of magnetic particles (~10 nm in diameter) in a liquid carrier. The carrier contains a surfactant, so that the particles won't clump together. Ferrofluids can be either water-based (the usual form for chemistry demonstrations) or organic-based (as in oils or fluorocarbons). A ferrofluid is about 5% magnetic solids, 10% surfactant, and 85% carrier, by volume. The ferrofluid described here uses magnetite for the magnetic particles, oleic acid as the surfactant, and kerosene as the carrier fluid to suspend the particles. When no external magnetic field is present the fluid is not magnetic and the orientation of the magnetite particles is random. However, when an external magnetic field is applied, the magnetic moments of the particles align with the magnetic field lines. When the magnetic field is removed, the particles return to random alignment. These properties can be used to make a liquid that changes its density depending on the strength of the magnetic field and that can form fantastic shapes. Ferrofluids are used to damp high-end speakers and the laser heads of CD and DVD players. They are used in low friction seals for rotating shaft motors and computer disk drive seals. You could open a computer disk drive or a speaker to get to the liquid magnet, but it's pretty easy (and fun) to make your own. -- How to Make Liquid Magnets - Materials and Safety Safety Considerations This procedure uses flammable substances and generates heat and toxic fumes. Please wear safety glasses, work in a well-ventilated area, and be familiar with the safety data marked on the chemical containers. Be advised that ammonia fumes are toxic. The resulting fluid is very strongly attracted to magnets and can splash, staining skin and clothing. Wear eye and skin protection when working with the ferrofluid. It is toxic - do not ingest it and keep it out of reach of children and pets. Materials * oleic acid (may be found in some pharmacies, craft, and health food stores) * household ammonia * PCB etchant (ferric chloride solution) - may be found at Radioshack * distilled water * steel wool * a strong magnet * kerosene * heat source * 2 pyrex beakers or measuring cups * a plastic syringe * coffee filters -- How to Make Liquid Magnets - Procedure for Synthesizing Magnetite The first step is to prepare the magnetite, which will be the source of the magnetic particles in the ferrofluid. First reduce ferric chloride (FeCl3) in PCB etchant to ferrous chloride (FeCl2), which will be used to make magnetite. Commercial PCB etchant is usually 1.5M ferric chloride, to yield 5 grams of magnetite. 1. Use the plastic syringe to measure and dispense 10 ml of PCB etchant into a pyrex or kimax measuring cup. Add 10 ml of distilled water. The etchant is diluted with water because there is an additive in Radioshack PCB fluid that can cause side reactions with the iron. 2. Drop a small piece of steel wool into the diluted etchant solution. Swirl the contents of the cup around until the liquid turns bright green (this is the FeCl2). 3. Filter the liquid through a coffee filter to remove the particulates. 4. Next, precipitate magnetite from the ferrous and ferric chloride solutions. Add 20 ml of PCB etchant (FeCl3) to the green solution (FeCl2). FeCl3 and FeCl2 react in a 2:1 ratio. The concentration of the FeCl2 just prepared is half that of the FeCl3 (because the water was added), so equal volumes will give the desired ratio. 5. Add 150 ml of household ammonia, stirring continuously. The ammonia reacts with the iron salts and excess chlorine to produce the magnetite, Fe3O4, which falls out of solution, in an ammonium chloride solution. The next step is to take the magnetite and suspend it in the carrier solution. -- How to Make Liquid Magnets - Procedure for Suspending Magnetite in a Carrier Next, the magnetic particles need to be coated with a surfactant, so that they won't stick together, even in a magnetic field, and suspended in a carrier, so the magnet will be fluid. 1. Coat the magnetite particles with oleic acid by heating the solution to just below boiling, in a well-ventilated area or under a fume hood. Stir in 5 ml of oleic acid. Keep the liquid near boiling until the odor of ammonia disappears (approximately one hour). Remove the mixture from heat and allow it to cool to room temperature. The oleic acids reacts with ammonia to form ammonium oleate. Heat causes the ammonium oleate to break down, allowing the oleate ion to enter into solution, while the ammonia escapes as a gas. The oleate ion attaches to a magnetite particle and is reconverted to oleic acid. 2. The coated magnetite is suspended in the kerosene carrier by adding 100 ml of kerosene to the coated magnetite suspension, again, in a well-ventilated area. Stir the suspension until most of the black coloration has left the water and has been transferred into the kerosene. Magnetite and oleic acid are insoluble in water, while oleic acid is soluble in kerosene. Stirring the mixure allows the coated particles to leave the aqueous phase in favor of the kerosene. 3. Decant and save the kerosene layer. Discard the water. The magnetite plus oleic acid plus kerosene is the final product, the ferrofluid. -- How to Make Liquid Magnets - Things to Do with Ferrofluid Ferrofluid is very strongly attracted to magnets, so always maintain a barrier between the liquid and the magnet. This can mean placing a sheet of glass or a container between the magnet and the ferrofluid. Be care of splashing of the liquid, from its strong reaction to the magnet. Both kerosene and iron are toxic, so do not ingest the ferrofluid or allow skin contact (don't stir it with a finger!). Here are some ideas for activities involving your liquid magnet ferrofluid. You can: * Float a penny on top of the ferrofluid, using a strong magnet. * Use magnets to drag the ferrofluid up the sides of a container. * Bring a magnet close to the ferrofluid to see spikes form, following the lines of the magnetic field. Explore the incredible shapes you can form using a magnet and the ferrofluid. Store your liquid magnet away from heat and flame. If you need to dispose of your ferrofluid at some point, follow your community's instructions for disposing of fuel oil or kerosene. Have fun! Learn More Here are some references and resources for more information about ferrofluids: * Ferrofluid Activity - http://mrsec.wisc.edu/Edetc/IPSE/educators/ferrofluid.html * Ferrofluid Movie - http://wohba.com/2005/10/magnetic-liquid-weirdness.html * Ferrofluid Sculptures - http://www.99express.com/posts/ferrofluid_sculptures.htm * Ferrofluid Synthesis - http://www.sci-spot.com/Chemistry/liqimag.htm * Liquid Magnet Used to Treat Cancer - http://english.pravda.ru/science/19/94/377/15259_cancer.html * Nickel Cadmium Sulfide Demonstrates Liquid Magnetic State - http://www.physorg.com/news6326.html * Rare Earth Magnets for Fun & Profit - http://www.dansdata.com/magnets.htm * Why Liquid Oxygen is Magnetic - http://www.physlink.com/Education/askexperts/ae493.cfm -- from sci-spot.com THIS PROCEDURE WILL SYNTHESIZE FERROFLUID. THIS MAGNETIC LIQUID CAN DEFY GRAVITY, CHANGE DENSITY, AND CAN FORM SPIKES WHEN NEAR A MAGNET. WARNINGS: THIS SYNTHESIS INVOLVES FLAMMABLE SUBSTANCES, TOXIC FUMES, AND HEAT. WEAR SAFETY GOGGLES, AND PERFORM IN A WELL VENTILATED AREA. FOLLOW EMERGENCY PROCEDURES MARKED ON EACH OF THE CHEMICALS' CONTAINERS. BEWARE THAT AMMONIA FUMES ARE TOXIC. ABOUT.COM HAS STOLEN THIS PAGE!! "Dr." Anne Helmenstine from About.com has stolen this content, word-for-word at times. Please write to Anne Helmenstine here and tell her what you think about her theft for profit. You can view her version of the site here. I have written to Anne, and she has flat out refused to acknowledge the obvious plagiarism: "Yes, your article is one I read when I wrote that tutorial. It was not, however, the only one, and I haven't copied you... You haven't been plagiarized. You have a one-page recipe for a ferrofluid. I have a 5-page resource, with background information and information on what to do with a fluid. I think it's obvious I didn't lift your text. Best wishes, Anne Helmenstine, Ph.D. About Chemistry" DESCRIPTION FERROFLUIDS ARE A STABLE (MEANING INSEPARABLE) SUSPENSION OF NANOMETER SIZED SOLID MAGNETIC PARTICLES IN A CARRIER FLUID. THE PARTICLES ARE COATED WITH A SURFACTANT; A CHEMICAL WHICH PREVENTS THE PARTICLES FROM CLUMPING TOGETHER AND FORMING A SOLID MASS. THE MOST COMMON TYPE OF FERROFLUID, PRESENTED HERE, IS AN OIL BASED FLUID CONSISTING OF MAGNETITE AS THE MAGNETIC SOLID, AND OLEIC ACID AS THE SURFACTANT. THE FINAL COMPONENT IS A CARRIER FLUID, WHICH SUSPENDS THE PARTICLES; IN THIS EXPERIMENT THE CARRIER WILL BE KEROSENE. FERROFLUIDS FIND USE IN HIGH END SPEAKERS, AS WELL AS HIGH PERFORMANCE SHAFT SEALS. SOME AQUEOUS FORMULATIONS CAN BE USED IN EYE SURGERY. OLEIC ACID IS A FATTY ACID, AND IS HISTORICALLY IMPORTANT FOR IT'S ROLE IN SOME OF THE FIRST SOAPS. SODIUM OLEATE, A SALT OF OLEIC ACID, IS STILL WIDELY USED IN SOAPS TODAY. THIS MOLECULE IS INTERESTING BECAUSE HALF OF IT IS SOLUBLE IN WATER AND HALF IS NOT. THIS MEANS, ESSENTIALLY, THAT ONE END IS 'STICKY' AND ONE IS NOT. THE MOLECULE'S STICKY END CAN ATTACH ITSELF TO A MAGNETITE PARTICLE AND WHEN THE PARTICLE IS COMPLETELY SURROUNDED, THE ACID MOLECULES KEEP THE MAGNETITE PARTICLES FROM STICKING TOGETHER. THIS IS THE SAME WAY SOAPS WORK; DIRT IS COATED AND MADE 'SLIPPERY' SO IT CAN BE WASHED AWAY. Materials -OLEIC ACID -HOUSEHOLD AMMONIA -PCB ETCHANT (FERRIC CHLORIDE SOLUTION) -DISTILLED WATER -STEEL WOOL -A STRONG MAGNET -KEROSENE Equipment -HEAT SOURCE -2 PYREX BEAKERS (MEASURING CUPS) -PLASTIC SYRINGE -COFFEE FILTERS THE FIRST PHASE IS TO PRODUCE FERROUS CHLORIDE FROM FERRIC CHLORIDE (PCB ETCHANT), WHICH WILL LATER BE USED TO PRODUCE MAGNETITE. NOTE THAT COMMERCIAL PCB FLUID IS 1.5M, SO THE AMOUNTS GIVEN BELOW WILL PRODUCE ABOUT 5 G OF MAGNETITE. 1. WITH THE PLASTIC SYRINGE, MEASURE 10ML OF FERRIC CHLORIDE (PCB ETCHANT) INTO A PYREX CUP. ADD 10ML OF DISTILLED WATER. THIS PORTION OF FeCl3 WILL BE REDUCED TO FeCl2. IT MUST BE DILUTED FIRST BECAUSE OF SOME ADDITIVE IN RADIOSHACK PCB FLUID THAT CAUSES SIDE REACTIONS WITH THE IRON. 2. ADD A SMALL PIECE OF STEEL WOOL. STIR OR SWIRL THE SOLUTION UNTIL IT HAS TURNED BRIGHT GREEN. FILTER WITH A COFFEE FILTER. FeCl2 IS BRIGHT GREEN AFTER FILTERING. EVEN BEFORE YOU FILTER YOU'LL NOTICE A COLOR CHANGE, BUT THERE WILL BE 'CRUD' FLOATING IN IT. NOW MAGNETITE WILL BE PRECIPITATED FROM A SOLUTION OF FERRIC AND FERROUS CHLORIDE. 3. ADD 20ML OF FERRIC CHLORIDE (PCB ETCHANT) TO THE GREEN FERROUS CHLORIDE SOLUTION FeCl3 AND FeCl2 REACT IN A 2:1 RATIO. THE CONCENTRATION OF FeCl2 IS HALF THAT OF FeCl3 (SINCE WE ADDED WATER), SO EQUAL VOLUMES PRODUCE THE REQUIRED RATIO. 4. WHILE STIRRING, ADD 150ML OF HOUSEHOLD AMMONIA THE AMMONIA PARTICIPATES IN A COMPLEX REACTION WITH THE IRON SALTS TO PRODUCE MAGNETITE, Fe3O4, WHICH FALLS OUT OF SOLUTION. THE AMMONIA REACTS WITH THE EXCESS CHLORINE, PRODUCING MAGNETITE POWDER IN AMMONIUM CHLORIDE SOLUTION. THE MAGNETITE WILL NOW BE COATED WITH OLEIC ACID. 5. IN A WELL VENTILATED AREA, HEAT THE SOLUTION TO NEAR BOILING. ADD 5ML OF OLEIC ACID, WITH STIRRING. CONTINUE TO HEAT NEAR BOILING UNTIL THE SMELL OF AMMONIA DISAPPEARS, USUALLY ABOUT AN HOUR. THE OLEIC ACID REACTS WITH THE AMMONIA TO FORM AMMONIUM OLEATE, A SLIGHTLY SOLUBLE SOAP. THE HEAT CAUSES THE AMMONIUM OLEATE TO BREAK DOWN, AND THE OLEATE ION ENTERS SOLUTION WHILE THE AMMONIA ESCAPES AS A GAS. THE OLEATE ION ATTACHES TO A MAGNETITE PARTICLE, AND IS RECONVERTED TO OLEIC ACID. THE COATED MAGNETITE WILL NOW BE SUSPENDED IN A CARRIER FLUID. 6. IN A WELL VENTILATED AREA, ADD 100ML OF KEROSENE TO THE COOLED SOLUTION. STIR UNTIL MUCH THE BLACK COLOR HAS LEFT THE WATER AND TRANSFERRED TO THE KEROSENE WHILE BOTH MAGNETITE AND OLEIC ACID ARE INSOLUBLE IN WATER, OLEIC ACID IS SOLUBLE IN KEROSENE. STIRRING ALLOWS THE OLEIC ACID COATED PARTICLES TO LEAVE THE AQUEOUS PHASE AND ENTER THE KEROSENE 7. POUR OFF AND COLLECT THE KEROSENE LAYER. DISCARD THE WATER. VOILA! THE KEROSENE HAS SUSPENDED THE MAGNETIC PARTICLES, AND IS NOW A FERROFLUID -- "J. Chem. Ed. in a past issue has a nice recipe for making ferrofluids. Isolation is especially easy. The commercial stuff is ball milled or attrited rather than precipitated." -- from wikipedia ferrofluid article Home-made fluid A simple ferrofluid can be home-made out of small magnetic particles mixed with mineral, vegetable or motor oil (sae10 or other lightweight). Iron filings do not work well; they are too big. Good sources for small magnetic particles are: * magnetic laser printer toner * magnetic inspection powder from welding shops * particles from burned steel wool (after mortar and pestle) * particles scraped from the surface of video tapes * particles "mined" from sand with a plastic bag and a magnet (see external links) * magnetic ink used to print checks A 1:1 ratio between the oil and magnetic powder seems to work best. These fluids are not very stable, however. The particles will tend to clump and the fluid properties will be lost quickly. Fluids created for professional purposes use emulsifiers to suspend very small oily (octane or kerosene) magnetic particles in water. The particles are very fine; less than a micrometre in diameter. They are created with a ball mill or attrition.[1] Ferrofluid stains are practically impossible to clean, so caution should be used when mixing or using. Berger, Patricia; Nicholas B. Adelman, Katie J. Beckman, Dean J. Campbell, et al (July 1999). "Preparation and properties of an aqueous ferrofluid". Journal of Chemical Education 76 (7): pp. 943-948. ISSN 00219584 ----------------------------------------------------- Sweet Spark May Hold Clue to How Things Break By KENNETH CHANG June 19, 2007 The Wint-O-Green Life Saver Effect, long of interest to children and adults chewing the candies in pitch-black closets to see the blue-white sparks shooting out of their mouths, could provide scientists a way to better understand how things break. At the atomic level, that is. Last month, scientists at the University of Illinois at Urbana-Champaign reported in The Journal of the American Chemical Society that those faint sparks were energetic enough to power chemical reactions along the fracturing surfaces. "When you break a pencil, you actually have to have broken chemical bonds," said Kenneth S. Suslick, a professor of chemistry at Illinois and one of the paper's authors. "Yet our understanding of that process is surprisingly poor. In fact when you look at the quantum mechanics of that, it isn't exactly clear how breakage occurs." Dr. Suslick said the sparks of light gave the opportunity to do spectroscopy, looking for specific colors of light given off by different atoms and molecules. That will give the scientists hints about how the bonds between atoms rearrange. "When you break materials, you're almost always going to be driving chemical reactions," he said. "It gives us a spectroscopic probe to see what's going on right at the fracture point." Reports of the Wint-O-Green Life Saver Effect -- the technical term is triboluminescence, which means light produced by rubbing -- goes back at least four centuries to Sir Francis Bacon, the English philosopher often considered the father of the scientific method. Bacon was of course not studying Wint-O-Green Life Savers, but he wrote in "Novum Organum," published in 1620, "It is also most certain that all sugar, whether refined or raw, provided only it be somewhat hard, sparkles when broken or scraped with a knife in the dark." Within a couple of centuries, other scholars realized this was great fodder for practical jokes. In 1753, Father Giambattista Beccaria wrote "A Treatise Upon Artificial Electricity." In it, he noted, "You may, when in the dark, frighten simple people only by chewing lumps of sugar, and, in the meantime, keeping your mouth open, which will appear to them as if full of fire." In general terms, scientists understand the how and why of triboluminescence. In some materials, including sugar and quartz crystals, electrons build up as the fracturing occurs and chemical bonds break. The charge build-up requires an asymmetric crystal structure or the presence of impurities. And then, just like a jolt of static electricity, the electrons jump to nitrogen or oxygen molecules in the air, which shed the excess energy by emitting light. Wint-O-Green Life Savers are particularly well-suited for observing this effect, because of the oil of wintergreen -- methyl salicylate -- that flavors them. Usually most of the light emitted by fracturing sugar is in the ultraviolet, out of view of human eyes. But the methyl salicylate absorbs the ultraviolet light and re-emits the energy as blue-green light. In the latest University of Illinois experiment, Dr. Suslick and Nathan C. Eddingsaas, a graduate student, started with a test tube filled with a slurry of small sugar crystals and liquid paraffin. A vibrating titanium rod immersed in the test tube generated ultrasound waves that created millions of tiny bubbles growing and collapsing in the paraffin 20,000 times a second. The shock waves slammed the sugar crystals together, and with nitrogen or oxygen bubbling through the slurry, the resulting bursts of light were typically 100 times, sometimes 1,000 times, brighter than the usual triboluminescence. The spectral fingerprints revealed the presence of carbon monoxide, carbon dioxide ions and other products of combustion. Further work will try to determine the chemical reactions occurring during triboluminescence. "It's basic science," Dr. Suslick said. "I don't see any applications, really. It's one of those things that have a long and illustrious history." J. Am. Chem. Soc., 129 (21), 6718 -6719, 2007. 10.1021/ja0716498 S0002-7863(07)01649-6 Web Release Date: May 5, 2007 Intense Mechanoluminescence and Gas Phase Reactions from the Sonication of an Organic Slurry Nathan C. Eddingsaas and Kenneth S. Suslick* School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 ksuslick@uiuc.edu Received March 8, 2007 Abstract: Mechanoluminescence is typically produced by grinding, crushing, or scraping a crystal, which can give a faint glow of light, and was first reported by Francis Bacon in 1605. This light is a microdischarge produced by the local separation of charged surfaces, resulting in a spectrum of gas line emission and the crystal itself. We have produced mechanoluminescence via a new route, using acoustic cavitation. Upon sonication of slurries of resorcinol in long chain alkanes, intense mechanoluminescence is observed, up to 1000-fold increase in intensity over grinding. We have observed extensive atomic and molecular emission lines that have not been previously reported for mechanoluminescence. In addition, we have evidence of gas phase reactions taking place during the mechanoluminescent event.