MAKE

A simple plug for one of my favorite magazines, MAKE.  After a few issues it spun off an artsier offshoot, CRAFT, which is now defunct.

One day when I have some extra time on my hands I’m going to pull out the old issue and start restoring old pinball machines, but for now it’s just a dream.  Actually, if I had that kind of time (and room in my basement), first I would build my own grappa distillation apparatus.

Solitons

We only address linear media in introductory physics classes, and really only focus on infinite or semi-infinite sine-wave-like disturbances.  In the real world waves have a finite duration; this type of wave is often called a wave packet.  If the wave is large enough, it can be affected by the nonlinear properties of the medium.  The most dramatic example of this is the soliton, a disturbance that propagates with no loss in speed, size or shape over large distances.

Though first observed more than 150 years ago, solitons weren’t understood until the last few decades and are still actively investigated in mathematics, physics and engineering.  This site gives an overview of current research as well as a historical account of the first description of a soliton on a canal in England.

Reflection FAIL

Physics textbook cover violates laws of physics.

Examine the book cover to the left closely; you can click on it for a larger version.  Notice the problem?

Let’s start by stipulating that it was unreasonable to actually photograph a real reflection of the Presidential Seal, so the publisher was justified in photoshopping it.  Keeping in mind that this is a real-life physics textbook, there are three schools of thought about the actual resulting book cover:

  1. Most charitable: this is all the publisher’s fault.  The author would have spotted this, but no one on the editorial side noticed it.  If only the illustrator had read the book (or taken the course it’s based on) this would never have happened.
  2. Less charitable:  at some point, some involved in this mishap realized that the reflection should have been inverted, but it was too much trouble to fix.
  3. Least charitable: the publisher knew the reflection job was botched but figured that the general public was
    1. too stupid to notice, and/or
    2. too stupid to comprehend reversed and distorted letters if the cover were fixed.

I understand the rationale for the reversed lettering on the front of ambulances: you want to avoid the split-second of incomprehension when a driver sees the ambulance in the rearview mirror.  But is the publishing industry really so cut-throat that the fraction of a second necessary for cognitive processing of a reversed Presidential Seal would have materially affect the sales of this book?

This one is even harder to explain.

Martingale

Here is a nice summary of the martingale (also known as the gambler’s ruin) for lay audiences.  This is really mathematics, applied here to the stock market / credit crisis, but it pops up in many other contexts.  In particular, the analysis is identical to first passage calculations that predict the speed of biomolecular motors or the time for a DNA binding protein to locate its binding site, and also to polymer physics descriptions of DNA confinement.

The article refers to a collaboration between a mathematician, statistician and physicist to decide whether a flipped coin really comes up heads and tails with equal probability.  Many concepts from introductory mechanics crop up in course of the collaboration, including projectile motion, angular momentum, air resistance, and experimental uncertainty.

Philosophical implications of Newton’s laws

I don’t have the time or, frankly, the inclination to deal with philosophy of science in a physics class.  Most of day-to-day physics is pretty practical, and the fact that Newton’s laws work (to the precision we require in most applications) is generally justification enough to use them.  However, people with a more highly developed philosophical sensitivity than mine may be concerned that Newton’s laws seem to rely on circular reasoning.  You can check out a lightweight summary of the issues involved; if that doesn’t dissuade you I suggest you take it up with the Department of Philosophy.

Swimming in goop

Chemical engineers at the University of Minnesota filled a swimming pool with guar gum (which should be familiar to anyone who reads food labels) to answer the age-old question “Can you swim faster in goop than in water?”

High Reynolds number hydrodynamics (roughly speaking, the study of large, fast things in water, where Re>1) is considerably more complex than low Reynolds number hydrodynamics (roughly speaking, the study of small, slow things in goop, where Re<1).  Since a swimming human operates in the complicated high Reynolds number regime (at Re ~ 4.5 × 106), there had been controversy about whether people would swim more or less quickly in viscous goop.

Short answer: it makes no difference whatsoever.  But lest you feel disappointed, this research did earn Cussler and Gettelfinger one of the highest-profile prizes in the natural sciences: an Ig Nobel!  Unfortunately, their goop only increased the swimming pool’s viscosity by a factor of two, which means that all else being equal (and, in fact, all else was equal because their test subjects swam at exactly the same speed as in water) the Reynolds number was only 2× smaller in the goop.  This is still very far from the simple yet weird physics that occurs at small Reynolds numbers.

The Great Molasses Disaster. Caused by deregulation of the molasses industry, no doubt.

Cautionary note: this experiment is sometimes incorrectly compared to swimming in molasses.  This is a dangerously bad analogy.  You can swim in a swimming pool filled with guar gum goop, but you cannot swim in molasses.  In fact, molasses are very dangerous.

Perpetual motion

This is an ad hoc list of physics-violating devices that have achieved sufficient prominence to make it onto the web.  Many have associated comment streams where you can read paranoid posts about sinister energy or oil cabals (OK – the oil cabal actually exists and even has its own web site) suppressing inventions that would free the world from the tyranny of energy scarcity.  In fact, the DARPA site for Breakthrough Propulsion Physics even includes a Cautionary Note:

“On a topic this visionary and whose implications are profound, there is a risk of encountering, premature conclusions in the literature, driven by overzealous enthusiasts as well as pedantic pessimists … Avoid works with broad-sweeping and unsubstantiated claims, either supportive or dismissive.”

Wikipedia has a short historical introduction to perpetual motion devices.  I have included only a few examples here, mostly just for fun.

An ancient unworkable machine. Since this predates the theory of conservation of energy, it's understandable.

Eric Krieg has an extensive list of perpetual motion machines, but seems to have abandoned his compilation around 2003 after some hundred entries.  Krieg seems to conclude that most of these devices’ “inventors” were nothing more than scam artists trying to bilk investors out of their money.  Luckily, my students understand conservation of energy and won’t be so easily parted from their lucre.   On a personal note: I had hoped the inventors were merely optimistic, or perhaps insane; apparently I’m naive.

Frustration with the whack-a-mole quality of these schemes is not new.  As far back as 1775, the French Academy of Sciences proclaimed that it would no longer consider any purported perpetual motion devices, because

“This sort of research . . . has ruined more than one family, and in many cases mechanics who might have rendered great services have consumed their fortune, their time, and their genius on it.”

Back then, perpetual motion machines were all mechanical, like the folding wheel (see figure).  Nowadays most – but not all – perpetual motion machines are electric or magnetic.

Please note that perpetual motion is possible, if you eliminate friction (for mechanical systems) or resistance (for electrical systems).  We know of exotic materials that are (under appropriate conditions) superfluids or superconductors: these will sustain flow or current forever with no loss.  However, these systems still do not produce any excess energy, and any energy extracted from them directly diminishes the amount remaining.

Energy for nothing

This person should know better.

Interestingly, proponents of these devices split into two camps: those who admit that they violate the known laws of physics, and those who claim to use only standard physical principles.  The former seem to revel in rebutting conventional science, while the latter portray themselves as clever engineers who merely exploit obscure loopholes in “normal” science.

  1. clearing house for schemes that promise to produce more energy than they consume. These are apparently called over unity devices.  Also weirder stuff that seems to veer toward UFOlogy.
  2. Orbo: some kind of rotary mechanical / electromagnetic device.  Proof that a nicely designed website doesn’t make something true.  I’d like to give Steorn (the company responsible for this device) credit for submitting the Orbo for review by a nonpartisan jury, but a few months after jury concluded that the device “[has] not shown the production of energy“,  Steorn claimed to have “resolved the key technical problems” and plans to market the Orbo in the near future.
  3. Motionless Electrical Generator.  Some kind of zero-point energy device (extracting energy from the vacuum).  Proof that acceptance by the U.S. Patent Office doesn’t make something true.  Bonus: the same guy who invented the MEG can also cure cancer.
  4. Lutec Electricity Amplifier: some kind of coupled AC/DC motor.  Proof that acceptance by lots and lots of patent officesdoesn’t make something true.
  5. Cold fusion: the claim that catalysts can cause deuterium fusion at normal temperatures and pressures.  This is a completely different category of unconventional energy generation, since there is no fundamental physics reason why cold fusion cannot exist.  Fusion certainly happens in the Sun and in the lab (in tokamaks), though at very high temperatures and pressures, and it certainly liberates large amounts of energy.  Fusion may well also occur at STP, but under normal conditions the rate of cold fusion is negligibly small, and it’s hard to see why a catalyst or electric current would increase that rate.  Most physicists would love cold fusion to be real; unfortunately, it appears that it’s not.
  6. Hydrino power.  Blacklight Power claims to have discovered a state of molecular hydrogen that has a lower ground state than the one we learn about in physics or chemistry: the hydrino.  They have a simple, highly exothermic chemical reaction that produces hyrinos.  This doesn’t violate any laws of thermodynamics – if the hydrino exists, it would be possible to build reactors that produce lots of cheap energy – but the hydrino is not an allowed solution to the laws of quantum mechanics as they are currently understood.  Blacklight Power has a rebuttal for that, of course.  Bonus: the company is located just down the road from my hometown of Princeton, NJ.
  7. Too-simple ways to increase your car’s mpg:
    1. Magnetic treatment of gasoline.  Not a perpetual motion device, but claims to improve fuel efficiency (and reduce carbon buildup and improve cooling system performance).  Apparently magnetism is so mysterious that people are willing to believe it can do just about anything.
    2. Plug-in mileage enhancer.  Insert in cigarette lighter and it increases fuel efficiency up to 30 percent, increases torque, and reduces emissions.  Bonus: improves car audio quality, too!

Momentum for nothing

Don't ask me how this is supposed to work.
  1. DARPA’s now-defunct “Breakthrough Propulsion Physics” Program reads like something out of The X-Files.  DARPA’s official technical site is rather heavy; the layperson’s summary is more accessible but light on the science; Wikipedia does a pretty good  synopsis.  Bear in mind that DARPA attempts a lot of really weird stuff that never pans out so the fact that it launched a program like this should not be taken as U.S. government endorsement of any of the physics therein.
  2. The Dean Drive looks like it falls under the DARPA category of “Oscillation Thrusters” characterized as “Non-Viable“.
  3. EM-drive.  Radiation pressure within a closed, tapered cavity supposedly causes the cavity to accelerate.