Seriously Inelastic

In physics we are usually taught that there are three types of collisions: elastic collisions, inelastic collisions, and completely inelastic collisions. Add to that the seriously inelastic collision.

Cocktail Party Physics: nascar driver vs. wiley coyote: a real-life seriously inelastic collision

Not for the squeamish — you should stick to ideal situations; this coyote is decidedly not spherical, especially after the impact. There is no truth to the rumor that NASCAR speedometers have a “purée” setting.

Getting the Latest Model is not Fashion

Dot Physics: The development of the atomic model

Ernest Rutherford said one day “hey, I think I will shoot some stuff at atoms.” I am sure his wife said “oh, Ernie” (she probably called him Ernie) “if it makes you happy to play with your little physics stuff, go ahead. I know how much you like it.” So he did. He shot some alpha particles (which are really just the nucleus of a helium atom) at some really thin gold foil.

One is the Loneliest Number

Magnetic Monopoles Detected In A Real Magnet For The First Time

Magnetic monopoles are hypothetical particles proposed by physicists that carry a single magnetic pole, either a magnetic north pole or south pole. In the material world this is quite exceptional because magnetic particles are usually observed as dipoles, north and south combined. However there are several theories that predict the existence of monopoles. Among others, in 1931 the physicist Paul Dirac was led by his calculations to the conclusion that magnetic monopoles can exist at the end of tubes – called Dirac strings – that carry magnetic field. Until now they have remained undetected.

I’m guessing (from the Dirac string reference) that these aren’t the monopoles of standard electrodynamics, forbidden by Maxwell’s equations, but another weird result from condensed matter physics, to go along with fractional charge and spin-charge separation. This subtlety is probably going to be lost on the scientific fringe, though.

Update: Yeah, as I suspected. Via Starts With a Bang, the abstract says these are “emergent quasiparticles resembling monopoles.”

Doing it Right

Illuminating physics for students by David Griffiths

Physics teachers are fortunate (I am among friends, so I can speak frankly): ours is a subject the relevance and importance of which are beyond question, and which is intrinsically fascinating to anyone whose mind has not been corrupted by bad teaching or poisoned by dogma and superstition. I have never felt the need to “sell” physics, and efforts to do so under the banner “physics is fun” seem to me demeaning. Lay out our wares attractively in the marketplace of ideas and eager buyers will flock to us.

What we have on offer is nothing less than an explanation of how matter behaves on the most fundamental level. It is a story that is magnificent (by good fortune or divine benevolence), coherent (at least that is the goal), plausible (though far from obvious) and true (that is the most remarkable thing about it). It is imperfect and unfinished (of course), but always improving. It is, moreover, amazingly powerful and extraordinarily useful. Our job is to tell this story – even, if we are lucky, to add a sentence or a paragraph to it. And why not tell it with style and grace?

Griffiths came down to Corvallis and gave a talk when I was in grad school. It was pretty good — I felt like I almost understood Berry’s phase when he was done. (OSU had its own David Griffiths; fortunately they did not annihilate upon meeting)

I found a particular resonance with this comment

I have known people who are in some sense too smart to be clear; they cannot remember what it was like not to understand something, because, I suppose, they never had this experience. They may be outstanding physicists, but they do not belong in the classroom.

When I was teaching, and later when merely explaining, I’ve tried to understand the misconceptions people have, and the barrier that the misconceptions create. It’s not enough to tell someone that their answer is wrong — they need to understand why it’s wrong, too. Remembering what it was like to not understand something is really useful.

Getting Loopy

Rhett analyzes a loop-the-loop; This is the same stunt (or is basically identical to the same stunt) I blogged about in May because the newspaper story summarizing it was so awful. But Rhett has graphs and charts and twenty seven eight-by-ten color glossy photographs with circles and arrows and a paragraph on the back of each one explaining what each one is. So check it out.

And Matt has the same topic but with half as many wheels, in Diavolo riding the loop on a bicycle.

My Turf

Built onFacts: Time and Navigation

Matt gives a brief summary of time and navigation. There’s one point that he glosses over, and it’s something that a lot of GPS summaries gloss over, to the point that they are misleading.

All a GPS satellite does is eternally broadcast two continuously updated pieces of information: its position and the time on its atomic clock. Knowing that light travels at about 1 foot per nanosecond, we can calculate how far we are from the satellite to the foot, as long as the GPS clock is accurate to the nanosecond and we have a receiver that can handle such a precise signal.

Actually you can’t do this unless you have a synchronized clock, and unless you’ve done this already, in order to synchronize the clocks properly you have to know … [wait for it] … the distance to the satellite. Many of the explanations of GPS completely miss this little tidbit. If you haven’t got a synchronized clock, and all you have are the GPS signals, you need four satellites to find your position. In practice four may not be necessary, because if you know your approximate position on the earth and have a topographic map, you can get the elevation from that, in which case three satellites is sufficient to get your position, to some level of uncertainty.

Grabbing the 'Aha' Moment

The US isn’t the only country having trouble teaching high-school physics. Australia has similar issues.

Physics teachers not up to scratch: study

One quote caught my eye:

“The person that’s teaching them might have some competence in science but just can’t grab that ‘aha’ moment.”

Not that I’m endorsing under-qualified high-school physics teachers, but I suspect that the ‘aha’ moment for science happens before high school. There are a lot of opportunities for teachers to turn students on, or off, before the teenage distractions show up in life. And physics tends to be taught last in high school science sequences, so the potential audience has already dwindled if students are turned off by chemistry or biology.

via