Category Archives: Physics

Serious Discussion

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Today’s Non-Sequitur

Quick thoughts: yes, it would fire. As Tommy Lee Jones reminds us, pistols (not just Glocks) can fire underwater, if you’re stupid enough to do so (like you’re performing DIY Shock wave lithotripsy) — they carry their own oxidant.

The bullet would travel faster, too. There would be less drag on the bullet, so it would not slow down as much as it does at one atmosphere. The muzzle velocity would only be epsilon faster, but the overall speed at some arbitrary distance would be higher.

I don’t understand why Danae doesn’t find that interesting.

(Blam! and Ping! not really happening, of course, in that rarefied atmosphere)

Update: the speed to orbit near the surface of the moon is about 1680 m/s. Not achievable with a pistol, but within the capabilities of some advanced weaponry. Escape speed (1.41 times higher) would require a Bull-like supergun.

Pick, Pick, Pick

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I spied a nit at which I must pick. This is something that’s become ingrained in certain science discussions, one of those innocent things that may or may not propagate a misconception and I’m sure it rarely causes an eyebrow to be raised, but, dammit, someone’s wrong on the internet.

Someone will tell me that energy is obtained because you’ve broken a chemical bond. It happens often enough that it’s not worth mentioning where I saw it (OK, OK, I’ll talk. It was Schwartz Matt) But seriously, it’s something you’ll run across a lot if you read stories about chemical processes and energy.

It’s one of those things that can be true but isn’t generally true. And the overall implication — that there is energy stored in the bonds which is released when you break them — is flat-out wrong.

Forming a bound state releases energy. Breaking apart that bound state requires the addition of energy. We can quantify the tightness of the bond by how much energy is involved, and that’s what we do with the enthalpy of formation: you have a baseline system — the free gases and atoms with which you start — which has (what we define as) zero energy. If you want to go from one bound system to another, you will release the difference in the enthalpies, because energy is conserved. (And if you look at more complex systems you involve the more and more complicated energies you find in thermodynamics) But the release of energy is in the formation of new, tighter bonds that are present in the products — that’s where the energy comes from. Burning those hydrocarbons is releasing energy not because you are breaking the bonds with the carbon and hydrogen, but because the bonds with the oxygen are stronger, and forming them releases the energy.

Schrodinger's Cat's Exam Score

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I was attempting to collapse a wave function Thursday — the A/C for the office has been taking much of the past week off, with promises of its imminent repair since Monday. The one working chiller has the capacity to cool the building only a few degrees below ambient, which was nowhere near adequate with the thermometer reading in the mid-90s (ºF). So rather than continue to self-baste at my desk, I wore shorts, hoping that this action would induce the chiller to be fixed, via a combination of superposition, Murphy’s law and passive resistance: a working chiller makes shorts both superfluous and marginally inappropriate, and all will subjected to my pasty-white legs until the system is fixed (and they are quite distracting, though I am informed that “running away screaming” does not count as swooning). Alas, the wave function did not collapse to the desired state, though it was a much more pleasant day yesterday, so my office was more-or-less tolerable.

But the thought of collapsing wave functions reminded me of a phenomenon I observed many times during the years I spent as an undergrad and grad student: the student who doesn’t show up to class when the exams are handed out. The professor will usually tell the class when the exams will be returned, and it’s often delayed one or two class sessions. In a small school, that’s because the professor is grading them him- or herself, and it takes time, and in a large university it’s often because they will be graded by the TAs, and most of them won’t do it until the night before (or wee hours of the morning of) the deadline. But there’s always that handful of students who don’t go to pick up the bad news, and it’s almost always bad news — from what I observed, the correlation is pretty strong between poor performance and not showing up to face the reality. For a long while I did not understand this, as it required going to the professor directly and asking for the exam, rather than being a momentary “Bueller” on the lips, though the propensity for the student to sit in the back of the class would add some time and attention to this evolution. Still, I don’t see that comparing to the one-on-one in the professor’s office.

But then I learned of coherent superpositions in quantum mechanics and it all began to make sense. One has not failed (or done poorly) on an exam until one has been handed the papers with all the red marks. Aha! By failing to retrieve the exam, all grades are still possible, and a poor one has not yet been earned. (Though that’s not quite right, either. Good grades are earned, poor grades are given. i.e. “I earned a ‘A,'” as opposed to ” the teacher gave me a ‘D'”).

(Update: Paraphrase: “Tom, it’s fixed. Put your damn pants back on”)

Physics at the Beach

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Sandcastle Science via physics and physicists

“[W]et sand’s strength is more or less constant for anywhere between one and 30 per cent water.” That’s because there’s a trade-off between the strength of each bond between the grains – which lessens as the sand gets wetter – and the number of bonds, which increases as the sand becomes more saturated.

A Relatively Good Concert

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Musical Relativity at the ArXiv blog

From the paper:

It is known that certain triads sound “happy”, while others sound “sad”.
Why this is so has been a question on minds of many musicologists, composers, musicians and
music lovers for a very long time and theories have been put forward. References to some works in
this area can be found in the recent book by Loy. But the question of “Why?” is beyond the scope
of this work. In this paper, we simply show that under specific physical conditions, a chord sounds
happy or sad depending not only on the observer’s subjective interpretation, but also on his frame
of reference. In other words, the musical “mood” depends on the observer’s state of motion.

In other words, “that note sounds flat!” becomes “you’re moving at the wrong speed!”

Just Stopped In

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to see what condition my condition was in

What’s Wrong with the Sun? (Nothing)

This report, that there’s nothing to report, is newsworthy because of a growing buzz in lay and academic circles that something is wrong with the sun. Sun Goes Longer Than Normal Without Producing Sunspots declared one recent press release. A careful look at the data, however, suggests otherwise.