"Browsing the Journals" Column  

I have collected together here the pieces that I have prepared for APS's Forum on Education Newsletters. Items have been updated where appropriate since the original columns were written.

  • Thomas Bensky and Matthew Moelter outline an introductory-level computer analysis of the kinematics and dynamics of a bead sliding on a frictionless wire on page 165 of the March 2013 issue of the American Journal of Physics. Art Hobson argues that the fundamental constituents of relativistic quantum reality are fields, not particles, on page 211 of the same issue. In a short note on page 313 of the April issue, we are reminded of how important it is to keep track of which variables are being kept constant during partial differentiation; that truth is particularly important in statistical mechanics, but the presented example contrasts the partial derivative of the kinetic energy with respect to a generalized coordinate in Lagrangian and Hamiltonian dynamics. Finally, Alejandro Jenkins tells us the history of a fraudulent perpetual motion machine on page 421 of the June issue that fooled even Leibniz and Bernoulli, while Selmke and Cichos draw an instructive analogy between Rutherford and optical scattering on page 405.
  • The February 2013 issue of The Physics Teacher has various descriptions of useful mechanics experiments: using buoyancy to measure the volume of a helium balloon on page 93 and to consider the change in apparent weight of an immersed object on page 96, and using an Atwood machine to measure dry axle friction in the pulley. On page 155 of the March issue, Frank Wang reminds us that a moving clock may not appear slow, owing to the finite signal propagation time from the clock to the observer. Speaking of motion relative to observers, that is what is important for the force on moving charges in a magnetic field, as discussed on page 169 of the same issue. Steve Iona reviews the 50 years of publication of TPT at the beginning of the April issue, and Mikhail Kagan solves the classic fox and rabbit chase problem by an elegant use of nonorthogonal coordinates on page 215.
  • A short but accurate calculation of Baumgartner's velocity of fall starting from 39 km above New Mexico is found on page 139 of the March 2013 issue of Physics Education. Some class demos about surface tension using soap films are presented on page 142. Mark Harrison compares impedance matching of resistors to perfectly inelastic collisions in mechanics on page 207. Ciocca and Wang discuss why moonlight often appears silvery or bluish on page 360 of the May 2013 issue, even though spectroscopically moonlight is redder than sunlight. Also don’t miss the contrast between blowing toward a candle from behind a menu, a wine bottle, or a funnel on pages 414 and 416. David Rowland has written another paper in his series about longitudinal motion for transverse string waves on page 225 of the March 2013 issue of the European Journal of Physics. Both journals can be accessed online.
  • I enjoyed Howard DeVoe's contrast of the local and global formulations of thermodynamics in the May 2013 issue of the Journal of Chemical Education. Be sure not to overlook the online Supporting Information in which he performs a computer-based Eulerian integration of the equations for a pinned vertical piston subject to wet friction (with vacuum on one side and an ideal gas on the other) that is suddenly released while the cylinder is immersed in a constant-temperature fluid reservoir.
  • If you make the effort to correct the large number of typos, there are some interesting comparisons of the times required for objects to move vertically due to gravity along various special paths on page 398 of the September 2012 issue of the Latin-American Journal of Physics.
  • The Fall 2012 Newsletter of the Society for College Science Teachers has a Teaching Tip by Paul Dolan in which he discusses the wide range of physics phenomena that can be presented using a ball on a string.
  • Geoff Dougherty recommends the Fulbright faculty exchange program on page 947 of the November 2012 issue of the American Journal of Physics. Do stars twinkle when viewed from Mars? Find out at the end of the article on page 980 of the same issue. I also appreciated the detailed book review of Mark Levi's (nb: not Mark Live's) book "Why Cats Land on Their Feet" on page 1112 of the December 2012 issue of AJP, together with an online link to a further list of comments on the book. I was amused by the explanation of why bubbles sink in stout beer glasses on page 88 of the February 2013 issue. (It has to do with the tilt of the sides of the glass relative to the vertical, but I think it's just an excuse to go out drinking.) Jeroen Spandaw shows that the principle of least action can be tricky to apply correctly on page 144 of the same issue: one needs to start with boundary values (two different fixed values of y) rather than initial conditions (values of y0 and v0).
  • Rod Cross's measurements of the viscoelastic properties of Silly Putty on page 527 of the December 2012 issue of The Physics Teacher motivated me to summarize the analysis in more detail. I was also intrigued by Göran Grimvall's brief discussion on page 530 of the same issue about presenting an unlabeled graph and several possible captions to students and asking them to figure out which is the only correct match. Finally, the article by Hester and Burris on page 534 shows that it is possible to derive the rocket thrust equation from Newton's second law if one is careful about choice of system, and Craig Bohren discusses cooling rates of humans in air and in water on page 560. In the January 2013 issue, you might be interested in the analysis of Baumgartner's supersonic balloon jump on page 14, the surprising longitudinal momentum imparted to air flow in the near-field of a sinusoidally driven loudspeaker on page 16, the question of whether a thin or a thick fuse connected in parallel across the same potential difference would burn out first on page 38, a lovely brief derivation for maximum range of a projectile fired off a tabletop on page 52 (I recommend having your students unpack some of the missing intermediate steps), and a wonderful Physics Challenge Problem on page 56 involving two Carnot refrigerators running in a tent.
  • Two identical balloons are filled, one with air and the other with helium, with their ends held pinched closed and then released together from rest. Which balloon will deflate most quickly? Which balloon will fly higher? How will they sound different as the gases escape? The key is the difference in their average molecular masses, as you can read about on pages 782 and 783 of the November 2012 issue of Physics Education.
  • Nature has reviewed the year 2012 in science. In particular, don't miss the interactive guide through key numbers and a summary of the year in review for science.
  • Usually I don't reference myself, but just for fun, you might read what the Chief of Naval Research said in Wired magazine about laser weapons and then read my related brief remarks in the local Annapolis newspaper.
  • Some effective demonstrations have been presented in recent issues of The Physics Teacher. Check out the use of a water-filled balloon to discuss buoyant force on page 428 of the October 2012 issue, and the counterintuitive behavior of series versus parallel springs on page 359 of the September 2012 issue.
  • A compact proof that M12 must equal M21 for the mutual inductances of two coupled circuits is provided by Dake Wang on page 840 of the September 2012 issue of the American Journal of Physics. I also enjoyed learning about the paradox of a floating candle that does not get extinguished on page 657 of the August 2012 issue, and the energy efficiency of the various systems in a car on page 588 of the July 2012 issue. The discussion on page 519 of the June 2012 issue of why shear is omitted from our standard discussions of divergence, gradient, and curl also intrigued me.
  • Connect a smaller spherical balloon to a larger one with a tube. It is not always the case that the smaller one will get smaller and the bigger one get bigger. See the experimental results and discussion on page 392 of the July 2012 issue of Physics Education. An aluminum soda can pull tab is floated on the surface of a glass of water. An electrostatically charged rod is brought near the tab. Does the tab move toward the rod, away from it, or stay still? See page 644 of the September 2012 issue for the surprising answer. Also check out the discussion of the volume of conical glasses and oval spoons on pages 502 to 504 of the July 2012 issue: half full is nowhere near half height! The journal can be accessed online.
  • The same webpage also gives a link to the European Journal of Physics. On page 1111 of the September 2012 issue, there is a discussion of particles sliding off the surfaces of arbitrarily shaped surfaces (not necessarily hemispherical as in the usual textbook case), with or without kinetic friction. Also see the discussion of the classic problem of whether or not one should run in the rain to keep as dry as possible on page 1321, and an analysis of the tumbling toast problem on page 1407 of the same issue. Finally, there is a good review of theoretical models and comparison to experimental measurements for falling U-shaped or piled-up chain systems on page 1007 of the July 2012 issue.
  • The June 2012 issue of the Journal of Chemical Education has a short but provocative discussion of how to define elements in contrast to compounds on page 832, and an article about how lightsticks work on page 910. Peter Loyson argues on page 1095 of the August issue that Galileo did not invent the Galilean thermometer. I was also sufficiently intrigued by the discussion of the laws of thermodynamics applied to open systems on page 968 of the July issue to write my own analysis.
  • Giovanni Organtini's model of a transistor as a flush toilet on page 221 of the April 2012 issue of The Physics Teacher is cute. The May 2012 issue of the American Journal of Physics has a theme on astronomy with many helpful articles for non-astrophysicists like myself: An explanation on page 376 of why the expansion of the universe does not result in the expansion of the size of atoms and other bound systems; a discussion on page 539 of a better way to explain star colors than using Wien's law; and a short but provocative calculation on page 417 that uses the uncertainty principle to estimate the time it takes for a pencil balanced on point to fall over.
  • On page 197 of the March 2012 issue of Physics Education, a nice explanation is provided of why modeling radioactivity by throwing 1000 dice and removing the ones that shows a 6 leads to a half-life that is systematically low compared to theory. The problem is that radioactive nuclei decay continuously while the dice "decay" in discrete steps as they are thrown. Other nice papers in the same issue include the discussion on page 152 of inverting a partly filled cup of water covered with a card and observing that the water does not all spill out, and a quantitative analysis on page 169 of a hanging rope slipping around a frictionless peg in terms of an Atwood machine with variable masses. The journal can be accessed online.
  • The same webpage also gives a link to the European Journal of Physics. On page 439 of the March 2012 issue, the melting ice-cube puzzle is discussed: When an ice cube floating in a glass of water melts, what happens to the water level in the glass? A previous publication shows the answer is it rises if we include the loss of buoyant force on the part of the ice that was above the water line. But this new paper shows the answer is it drops if we also include the thermal contraction due to the heat required to melt the ice. On page 467 of the May 2012 issue, a nice discussion appears about how to avoid artificial infinities when calculating the electrostatic potential of an infinite line charge.
  • There is a vigorous debate in the letters in the April 2012 issue of the Journal of Chemical Education about whether it's time to retire the model of hybrid atomic orbitals.
  • I appreciated Chunfei Li's model for how the bowing of a track down which a cart is rolling will lead to an apparent violation of conservation of mechanical energy in the March 2012 issue of the Latin-American Journal of Physics Education.
  • One of the reasons I love reading educational physics articles is that they often force me to rethink familiar physics explanations for phenomena. An excellent example is the article by Héctor Riveros on page 52 of 2012 Issue 2 of the relatively new European Journal of Physics Education. He challenges explanations for three common demonstrations: that when the end of a ruler protruding from under a sheet of newspaper at the edge of a table is given a sharp blow it breaks because of air pressure on the sheet; that water rises into an inverted jar covering a burning candle in a tray of water because the candle consumes the available oxygen; and that a stream of water is attracted to an electrically charged balloon because water is polar.
  • Harvey Leff has begun a five-part series of articles on demystifying entropy on page 28 of the January 2012 issue of The Physics Teacher. In addition, two articles particularly caught my eye in the December 2011 issue. Craig Bohren discusses convective and radiative cooling in "Why do objects cool more rapidly in water than in still air?" He points out that a person can survive a long time in still air at 7oC but not in water at the same temperature. Secondly, on page 567, an experiment is performed to measure the slipping angle of a ladder leaning against a wall when there is friction at both the floor and wall, unlike the usual textbook case that assumes a smooth wall. I have been interested in this same problem, but it is the clever technique used here to keep the two ends of the ladder perpendicular to the floor and wall that validates the theory.
  • Under the editorship of David Jackson, the American Journal of Physics is continuing to publish a diverse range of interesting problems. Check out Behroozi's article in the Nov. 2011 issue experimentally relating the internal pressure of soap bubbles to their radius and surface tension. In the Dec. issue, learn about video measurements of the added mass of a thrown beach ball, arising from the fact that the moving ball must accelerate some air around it. There is also a fabulous brain twister involving a falling block that is connected by a string and pulley to a second block sliding on a frictionless horizontal track. On page 24 of the Jan. 2012 issue are measurements of the muzzle velocity of a compressed air cannon; it turns out that primary disagreement with simple theory is not because of friction as the ball moves down the barrel, but because of the pressure drop as air flows through the valve between the pressure tank and the gun. Finally, I found Corti's note on the Gibbs paradox in the Feb. issue to be particularly enlightening in understanding the tricky issue of distinguishability of ideal gas particles.
  • Most of us are probably familiar with the idea that one can tell the Earth is round because the mast of a ship progressively sinks below the horizon as it sails straight away from shore. Kibble puts some numbers on a photo of a distant bridge to calculate Earth's radius on page 685 of the November 2011 issue of Physics Education.
  • The same webpage also gives a link to the European Journal of Physics. The November 2011 issue has an article by David Rowland and three letters by Butikov, by Burko, and by Repetto et al.discussing the surprisingly complicated matter of the correct expression for the potential energy density of a transverse wave on a string. The issue is that one needs to take correct account of longitudinal motion of string segments, which must occur if the stretching is uniform along the string. I have collected together some related discussions from the past decade of the momentum carried by mechanical waves.
  • The November 2011 issue of Journal of Chemical Education has an article by Fieberg and Girard suggesting a pie mnemonic for relating the various thermodynamic potentials such as enthalpy and Helmholtz free energy, along with the corresponding Maxwell relations.
  • The Fall 2011 issue of the Center for Excellence in Education Newsletters interviews a number of physicists about the issue of Physics First in high schools.
  • Rod Cross has an article in the October 2011 issue of The Physics Teacher concerning what happens to a car when it drives off the end of a ramp. After the front wheels lose contact but the rear wheels have not, the car will begin to rotate downward about its center of mass. This has real-life implications, as a vehicle that drove off the top of a sand dune in Australia landed nose down and then rolled onto its roof, seriously injuring a passenger. Also the September 2011 article about the "magic trick" of a ring falling and getting knotted in a chain reminded me of the demonstration show at the Summer AAPT meeting about the physics of magic.
  • A pair of physicists ask "Is the electrostatic force between a point charge and a neutral metallic object always attractive?" in the August 2011 issue of the American Journal of Physics. Of course, they would not ask unless the answer were no, but you will have to read the article yourself for a specific worked-out example.
  • I teach at the U.S. Naval Academy. It's amazing how much the midshipmen love shooting stuff. Read about some video measurements that a student and a military instructor made of a potato bazooka on page 607 of the September 2011 issue of Physics Education.
  • The same webpage also gives a link to the European Journal of Physics. The September 2011 issue has lots of interesting articles: how a reverse sprinkler is related to a putt-putt boat and an unclamped garden hose wildly spraying around on page 1213; video evidence on page 1245 that a piece of paper placed on top of a book and dropped with it is not in free fall; a discussion on page 1293 of why it is difficult to ride a real bicycle on top of rollers; and measurements of axle friction on page 1367 for a rotating disk.
  • The June 2011 issue of the Latin-American Journal of Physics Education has a paper comparing series and parallel networks of Atwood machines to familiar resistor circuits.
  • The July 2011 issue of the Journal of Chemical Education has several interesting pieces: some thermodynamic measurements of cups of water using an infrared camera on page 881; examples of using computer software to calculate propagated errors on page 916; and use of atomic units on page 921.
  • The Fall 2010 issue of the International Commission on Physics Education Newsletters leads off with an overview of ComPADRE by Bruce Mason.
  • Finally, APS's Spotlight recently highlighted an article entitled "Strongly Modified Spontaneous Emission Rates in Diamond-Structured Photonic Crystals" in Physical Review Letters that succeeds in demonstrating a greater than one order of magnitude reduction in spontaneous emission of quantum dots embedded in a three-dimensional photonic bandgap structure.
  • Elisha Huggins has a three-part article on Special Relativity in the March, April, and May 2011 issues of The Physics Teacher. Also be sure to read Michael Grams's two-part discussion of whether students should be provided solutions to homework problems (and if so, from Cramster or from the textbook publisher?) to help them learn physics in the April and May issues.
  • I found Swendsen's article about the meaning of entropy in the April 2011 issue of the American Journal of Physics to be thought provoking. I also appreciated Lewis's Letter to the Editor in the same issue that we should start reporting the range of visible light in terms of hundreds of THz rather than only in terms of hundreds of nm.
  • There has been some controversy about the relative roles of gravity and of atmospheric pressure in the operation of a siphon. The May 2011 issue of Physics Education has some useful ideas and demonstrations related to this matter, such as what happens when there is a large air bubble in the siphon line or if the siphon tube runs into another wider diameter tube which runs into the reservoir. I also was intrigued by the demonstration on page 290 of the same issue about constructing a Faraday cage by enclosing a cell phone in a tin can sealed off with foil and punching a hole of increasing diameter in the foil until the phone rings.
  • The 1 March 2011 issue of the Latin-American Journal of Physics Education has a paper discussing the motion of a ball rolling on a spinning turntable. The trajectories are conic sections and are analogous to motions of charged particles in crossed electric and magnetic fields.
  • The 1 May 2011 issue of the Journal of Chemical Education has a nice discussion of using the Metropolis algorithm in an undergraduate thermodynamics course on page 574. Successive pages in the same issue have five articles that consider phase diagrams and entropy that should also be of interest to the same audience.
  • The online version of Physics World has an interesting discussion of the measurement of the thermal Casimir force (due to thermal fluctuations in the electromagnetic field between two objects).
  • The February 2011 issue of Science online has a surprising demonstration that under certain circumstances it can be easier to push a can whose top end is closed into a sand pile than an otherwise identical can open at both ends.
  • Many people (myself included) are interested in the physics of potato guns. Mark Denny has a very accessible analysis of how the muzzle speed and mechanical efficiency depend on the barrel length in the February 2011 issue of The Physics Teacher. I also enjoyed thinking about the "Direction of Friction" for a cylinder rolling without slipping up and down an incline in Paul Hewitt's January 2011 Figuring Physics column. Finally, if you teach thermodynamics, you may wish to consider Todd Timberlake's suggested coin-flipping activities on page 516 of the November 2010 issue.
  • The February 2011 issue of the American Journal of Physics has an article beginning on page 193 that compares theory and experiment for some extensions of the familiar demonstration of dropping a magnet down a conducting pipe: What happens if you drop two magnets? How does the magnetic braking force depend on the distance between the magnet and the pipe wall? In the January 2011 issue, the article "Listening to student conversations during clicker questions" gave me some interesting new ideas to help me improve my use of student response systems in introductory physics.
  • I enjoyed the various tidbits in the End Results section of the January 2011 issue of Physics Education. Also, the old chestnut of whether one should walk or run in the rain to minimize how wet one gets is discussed on page 355 of the March 2011 issue of the European Journal of Physics. Both journals can be accessed here.
  • The 1 January 2011 issue of the Journal of Chemical Education discusses the issue of dimensional analysis involving transcendental functions (such as sine or logarithm) on page 67.
  • I was intrigued by the discussion of how a fly can walk upside down on a ceiling without falling off in the online version of Physics World. Apparently the secret involves an emulsion of two different fluids secreted by a fly's feet.
  • APS recently highlighted an article in Physical Review Letters. about a state-of-the-art determination of the Avogadro constant. I find it to be an interesting exercise to brainstorm with students various ideas for how one might determine the values of such constants.
  • Beginning with the September 2010 issue of The Physics Teacher, one article per issue will be selected and supplemented with an interactive computer model developed using the Easy Java Simulations (EJS) code with the assistance of Wolfgang Christian. In this first issue, the article selected is "Calibration of a Horizontal Sundial" and includes three EJS models which illustrate the geometry of a north-oriented sundial's shadow for different latitudes and times of day. In the same issue, be sure to read the enlightening Letters to the Editor by John Mallinckrodt and by Eugene Mosca, reminding us that force is not equal to the derivative of momentum for a system of "variable mass."
  • American Journal of Physics is also selecting one article per issue to supplement with EJS models. The October 2010 issue chose "A close examination of the motion of an adiabatic piston," which includes a link to a molecular dynamics simulation in which a box is partitioned by an insulated piston that is jostled back and forth by two different Lennard-Jones gases in the two sides of the box.
  • The September 2010 issue of Physics Education has a great way to demonstrate Poisson's spot in class. All you need is a laser pointer and a pin with a round head, which is much simpler than the typical setup using collimation optics and a video camera. The September issue of the European Journal of Physics discusses in "A thermal paradox" the question of which reaches a higher steady-state temperature: a thin or a thick plate of the same material uniformly illuminated on one face by a constant beam of light? Theory is compared with experimental results. Both journals can be accessed online.
  • A couple of articles caught my eye in the October 2010 issue of the Journal of Chemical Education. Page 1039 quantifies the hearing risk associated with exploding balloons containing hydrogen gas in class. Then on page 1071, a mechanical apparatus is discussed to model the Morse potential for anharmonic diatomic bonds.
  • The Journal of Science Education and Technology recently published online an article entitled, "How the Discovery Channel Television Show Mythbusters Accurately Depicts Science and Engineering Culture."
  • You don't rate a chili pepper on RateMyProfessors.com? Well, maybe you or a colleague is a pizza slice or a harmonica instead! Check out the proposed new icons in the Chronicle of Higher Education.
  • The May 2010 issue of The Physics Teacher has a short but insightful article by Elisha Huggins about weighing a hollow cube whose walls are coated with mirrors between which a photon is bouncing. Does it matter whether the photon is bouncing vertically or horizontally? Also check out Boris Korsunsky's Physics Challenge entitled "Be There and Be Square" in the same issue. But beware because this problem is much harder than some of the ones in preceding issues!
  • I enjoyed the interesting variety of Notes and Discussions in the June 2010 issue of the American Journal of Physics.
  • The May 2010 issue of the Latin-American Journal of Physics Education has a lengthy article entitled the "Sliding rope paradox" which discusses a rope suspended over a frictionless peg off of which it is sliding. The connection with the well-known falling chain problem is also considered.
  • There have been plenty of arguments about how airplane wings create lift. The most recent article on this topic is by Silva and Soares in the May 2010 issue of Physics Education. Another well-discussed problem is that of crossing a river in a boat. O'Shea considers some complications involved in that task in an article in the July 2010 issue of the European Journal of Physics. Look for both journals at http://iopscience.iop.org/journals.
  • The Journal of Chemical Education has finally implemented a fully electronic submission procedure and a spiffy new webpage for accessing their journal. You might be interested in one chemistry educator's heuristic interpretation of quantum mechanics on page 559 of the May 2010 issue.
  • Some interesting letters to the editor appeared in the May 2010 issue of Physics Today, stimulated (excuse the pun) by the January 2010 article about the discovery of the ruby laser in 1960.
  • Finally, Art Hobson of the University of Arkansas passed along the following. The Jan-Feb 2010 issue of Environment has an article entitled "Now is the time for action" authored by 16 members of the National Science Foundation's Advisory Committee for Environmental Research and Education. They argue that "environmental issues must become a priority for the security of citizens and governments around the world," that "the world is at a crossroads" with "little time to act," and that "conducting research and education via a model of business-as-usual will not be sufficient." The Committee makes five recommendations: (1) increased support for interdisciplinary environmental research; (2) NSF must become a more interdisciplinary organization that attracts integrative research and education; (3) NSF must lead in implementing an integrated system of observational sensor networks that measure environmental variables and related human activities; (4) new approaches are needed for environmental education and public engagement; and (5) scientists must help policymakers develop a better understanding of environmental systems, including tipping points and the socio-economic effects of environmental change.
  • The November 2009 issue of The Physics Teacher has an unusually large number of articles with insightful physics experiments and theory, including discussion of cosmic ray detection, inverse-square forces, the Coanda effect, back emf, static equilibrium, general relativity, capillary rise, terminal velocity, the Coriolis force, and boomerangs, among many other topics.
  • I enjoyed the Quick Study entitled "The surprising motion of ski moguls" on page 68 of the November 2009 issue of Physics Today. It clearly explained how moguls form (with what characteristic spacing and amplitude) and why they slowly migrate uphill by about 8 cm per day. Get out your skis and test some physics in action!
  • A French trio present a pedagogically instructive mechanical model for a Carnot engine on page 106 of the January 2010 issue of the American Journal of Physics. The hot reservoir consists of a partially filled egg carton of balls located vertically higher than another egg carton comprising the cold reservoir. The mean and standard deviation of the gravitational potential energy and configurational entropy are easily calculated, and therefore also the effective reservoir temperatures and the engine efficiency.
  • Recently in our department there has been discussion of how to best experimentally investigate and model damped oscillations of a mass on a spring. So it was with great interest that I noticed an article on page 121 of the January 2010 issue of the European Journal of Physics. Three physicists from Colombia present data for a sphere oscillating in aqueous glycerin solutions of different concentrations and container sizes. They show that it is necessary to introduce corrections to the standard Stokes model in order to fit the data.
  • The November 2009 newsletter of the International Commission on Physics Education includes an article entitled "Recent Developments in Physics Education in Canada."
  • A set of MathCad symbolic mathematics programs and associated documentation for various topics of relevance to thermodynamics and statistical mechanics are included in the December 2009 issue of the Journal of Chemical Education, as can be accessed online.
  • David Griffiths (recently retired from Reed College) has an article with his thoughts about teaching physics entitled "Illuminating physics for students" in the September 2009 issue of Physics World.
  • In the October 2009 issue of The Physics Teacher, H.K. Wong points out on page 463 a flaw in a simple explanation of a unipolar motor (made of a battery, nail, rare-earth magnet, and wire) that I have often demonstrated in class. The torque which rotates the magnet cannot be due to the internal current flowing through the magnet. Instead it must arise from a reaction to the force that the magnet exerts on the wire near the point at which they touch each other.
  • I enjoyed Jeremy Bernstein's biographical ruminations about Dirac (and other physicists of his era) on page 979 of the November 2009 issue of the American Journal of Physics.
  • I find simple demonstrations of atmospheric buoyancy to be amusing and instructive. The November 2009 issue of Physics Education discusses two. On page 668, a person stands on a scale while wearing a Santa suit that can be filled with air. Does the scale reading change noticeably? On page 569, a syringe (with its tip capped off) is placed on a sensitive balance. Does its measured weight depend on whether the plunger is pressed in or pulled out? In one case the answer is no and in the other the answer is yes. If you add a volume of air to an object, both the gravitational and buoyant forces increase by the same amount, unless the added air is at a substantially different pressure than the surrounding atmosphere. (Now you're ready to try the alka-seltzer in a latex glove demo that Harold Stokes presented at an AAPT meeting a few years ago.)
  • A couple of papers caught my eye in the most recent two issues of European Journal of Physics. On page 1173 for September 2009, Agrawal discusses a simplified version of the Curzon-Ahlborn (CA) engine. Unlike a Carnot device which optimizes the efficiency but at the expense of infinitely slow operation, a CA engine maximizes the rate at which work is output. Secondly, using a numerical wind-tunnel model on page 1365 of the November issue, a Spanish pair of applied physicists show that bicyclists traveling as a tight group benefit not only the behind riders (by drafting) but even the cyclist at the front of the pack!
  • A pair of Russian researchers present a detailed vector kinematics solution to the dog-and-rabbit chase problem starting on page 539 of the September 2009 issue of the Latin-American Journal of Physics Education.
  • A brief overview of photoacoustic spectroscopy of nanomaterials can be found on page 1238 of the October 2009 issue of the Journal of Chemical Education. This technique is particularly appropriate for materials that scatter light too much to be easily studied by conventional absorption spectroscopy. The idea is to place a sample in an air-tight chamber, hit it with a chopped laser so that the sample and hence the surrounding air is periodically heated, and measure the resulting pressure oscillations with a microphone.
  • In the May 2009 issue of The Physics Teacher, Vincent Toal and Emilia Mihaylova present a two-page article entitled "Double-Glazing Interferometry." They explain how one can easily see white-light fringes by looking at the full moon against a black night sky through a double-paned window at an angle. A secondary image of the moon with interference fringes appears beside the moon. I found it also worked to look at a large street lamp, so there's no need to wait for a full moon. I must admit I have often seen such secondary images previously through my house windows at night but had not taken any notice of them, a demonstration of the fact that "discovery activities" need to be guided to be truly effective.
  • An article entitled "On the stability of electrostatic orbits" in the May 2009 issue of American Journal of Physics discusses the stability of two charged conducting spheres orbiting each other in free space. Effects of charge polarization and dependence on the orbital angular momentum are analyzed. The first two references in the paper are to the actual demonstrations of such orbits using graphite-coated styrofoam spheres aboard the "Vomit Comet" aircraft by undergraduate students.
  • In the featured paper "A simple demonstration of a general rule for the variation of magnetic field with distance" in the May 2009 issue of Physics Education, a Japanese geophysicist discusses a simple method to measure the variation in magnitude of the field with distance along the axis of a small permanent magnet using only an ordinary compass. The idea is to position the magnet's axis to be perpendicular to earth's magnetic field so that the tangent of the compass needle's deflection angle gives the ratio of the magnet's field strength to that of the earth. The connection to the magnet's dipole moment is analyzed.
  • "A simple derivation of Kepler's laws without solving differential equations" in the May 2009 issue of European Journal of Physics presents an elegant geometrical derivation of Kepler's three laws where the force of gravity is approximated as a succession of impulses (so that the orbit is an elliptically shaped polygon). The key step is to introduce the Runge-Lenz ("eccentricity") vector to obtain the equation of an ellipse in polar coordinates.
  • A fairly new journal, featuring pedagogical physics articles in both English and Spanish, is the Latin-American Journal of Physics Education, published in January, May, and September. For example, the May 2009 issue includes articles about laboratory determinations of Malus's law, properties of a pendulum, and Planck's constant.
  • The International Commission on Physics Education puts out a Newsletter twice a year. As might be expected, it features articles and advertises conferences that promote physics education in different geographical areas of the world.
  • From time to time, the Journal of Chemical Education has articles of interest to physics educators, particularly in the areas of thermodynamics and statistical mechanics. A notable example is the January 2009 issue whose "Research: Science and Education" section focuses on articles discussing entropy, the Clausius-Clapeyron equation, and the virial expansion.
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