Category Archives: Physics

I Come to a Different Conclusion

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There’s a video out there in the ether that purports to measure time dilation in a car. I’ve already shown that this can, and does, happen, but you need to have some pretty expensive toys at your disposal to make the measurement.

For a good experiment (I’m perhaps charitably assuming this wasn’t just an out-and-out fraud), one would also want to measure the stopwatches against each other to make sure they were running at the same rate, and calibrate them if they weren’t. Ideally you’d want several clocks, but that’s a little advanced for this level of execution. Then, you’d want to make sure that you weren’t perturbing the clocks with different environments, like temperature differences, so make sure you aren’t blasting the AC on the stopwatch. Finally, you’d want to predict the difference to compare it to the measured difference. Ignoring effects from any elevation changes, a half-hour trip at 60 mph is going to give you a dilation of around 7 picoseconds.

My conclusion is that your stopwatches suck.

Not Even the iPhone Can Do This

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The teaser for the evening news just showed a clip of cellphones purportedly popping popcorn, and asking the question of whether it’s a hoax. My money’s on yes. Wired has a story on it, and there’s more than one video.

Assume a kernel has 0.1 g of water in it. You need to heat it from ~20 ºC to 100 ºC and then boil it, which is what happens when you pop popcorn. The heat capacity is 4.18 J/g, and the heat of vaporization is 2260 J/g. So this requires 80*4.18*0.1 +2260 * 0.1 = 260 Joules. This happens in a few seconds, so the absorbed power is somewhere around 50-100 Watts, per kernel. The transmitted power of the phones would have to be much, much larger, since it’s not focused on the popcorn.

Not.

Google also tells me that Zapperz beat me to the punch here.

Update: It looks like I overestimated the water content by a factor of about 5 (see link in comment 2; I assume medium-large kernels, though, not small. Orville has standards). Doesn’t change the overall answer. It takes my microwave oven ~3.5 minutes to pop my popcorn. A few hundred Watts for a (few) hundred kernels so let’s call it 1 Watt per kernel for 270-330 seconds (onset of popping is at about 2.5 minutes). That matches up pretty well with the numbers above, which we now know are overestimated. I see no reason to hypothesize that only infinitesimal boiling is happening.

Release the Press Hounds!

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I was poking around the toobz (looking for a citation or link to something about “slow light”) and ran across this press release from last year that made me clench and then start grinding my teeth. I have no idea who vets these things, but OMFG, it’s bad. The press latches onto these ideas that are just wrong, and use cutesy buzzwords and phrases to try and connect the story to the urban-legend version of physics that the popular-press readers know, partly because that’s what gets fed to them by the popular press. It becomes that much harder to undo the damage once the bad information gets ingrained, much like when superluminal physics gets reported, only to invariably find it’s anomalous dispersion, and nothing has “broken the lightspeed barrier” or in any way violated relativity.

Here’s the press release: Light and Matter United

Let me say, at the outset, that Lena Hau, et. al, do some amazing, quantum jaw-dropping atomic physics, and I’m not making any arguments or objections about that work. What I’m critiquing is how that work is being reported.

Lene Hau has already shaken scientists’ beliefs about the nature of things. Albert Einstein and just about every other physicist insisted that light travels 186,000 miles a second in free space, and that it can’t be speeded-up or slowed down. But in 1998, Hau, for the first time in history, slowed light to 38 miles an hour, about the speed of rush-hour traffic.

It’s well-known that light traveling through a medium does so at a speed slower than c, and the light that was slowed down wasn’t in a vacuum, so WTF? It was in a specially-prepared sample of a Bose-Einstein Condensate (BEC), called Electromagnetically-Induced Transparency (EIT), which creates a narrow window (in frequency-space) where light won’t be absorbed, and near a resonance you get a change in index of refraction. A rapidly-varying index of refraction, as you get here with a sharp resonance, will slow down the group velocity of light by a large factor. As one can read in the paper (pdf),

[W]e obtain a nonlinear refractive index of 0.18 cm2W-1. This nonlinear index is ~106 times greater than that measured in cold Cs atoms

So the experiment was way cool, but not something that shakes one’s belief about relativity, and the whole bit about the speed of light in a vacuum is a head-fake.
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A for Effort. C for Content.

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Via Talk Like a Physicist, an ad campaign by Science World in Vancouver BC. (and I have a vague recollection of visiting it back when I lived slaved there as a postdoc)

science_world_scale.jpg

I can’t find any link to this at the Science World web site but then this is apparently from a little while ago (other ads I found are dated 2006). So I can’t verify what was said in the pamphlet that was supposed to be included with the scale, because, of course, you only “weigh less” as long as the elevator is accelerating down. After it reaches “cruising speed” you weigh the same, and when it accelerates in the upward direction to bring you to rest, you “weigh” more, all happening on the way down. This reminds us that the scale is measuring the normal force, and not the weight, which is what I hope the pamphlet pointed out.

Another way to test this is to jump right as the accelerator starts down. In the ones that really zip, you can hit your head on the ceiling as the elevator accelerates while you are in a ballistic trajectory.

More Advice for the Physicslorn

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Still catching up from more than a day (and more than a blog-cycle) without power. Guide for the Amateur Physicist, which (if I were to have input) might be subtitled “This is why your missive isn’t science,” or, if I were Mike Myers in an SNL sketch, it might be “If it’s not physics, it CRAP!”

[U]ntil your theory can be described mathematically, it has no hope of making clear predictions about the results of experiments. You must be able to get actual numerical answers to problems using your theory. This is an ironclad requirement.

Which renders the (unfortunately all-too-common) “My ‘theory’ has no math. Can you please verify it?” inquiry moot.

Twisted Sister

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Jennifer Ouellette has a new blog, not the same as the old blog, at Discovery. Check out Twisted Physics. She promises shorter posts than on Cocktail Party Physics, which isn’t going away.

Rest assured, Cocktail Party Physics isn’t going anywhere. It will continue much the same, staunchly independent and wheezily long-winded.

No word yet on whether we will be able to observe her in a superposition of the two blogs, or what might happen if that wave function collapses.

Not Pretty

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A doctor tells a man, “You’re fat. Lose some weight.”
The man says, “I want a second opinion.”
“OK, you’re ugly, too.”

According to the International Journal of Obesity, we’re fat because we’re stuffing our faces, and not so much because we’re sitting on our duffs (Ha! Speak for yourself. I’m a double-threat.)

(from the journal)

Conclusion: As physical activity expenditure has not declined over the same period that obesity rates have increased dramatically, and daily energy expenditure of modern man is in line with energy expenditure in wild mammals, it is unlikely that decreased expenditure has fuelled the obesity epidemic.

So if you’re burning just as many (or more) Calories, gaining weight must be from increased intake. Basic physics.

And as for the International Journal of Obesity? From this angle it looks to be a few extra pages thick, if you take my meaning.