1,326 reputation
38
bio website
location
age
visits member for 3 years, 7 months
seen Jan 26 '12 at 20:37

Apr
26
comment What is the force on the arms in a pushup?
I've done this before with the scale - to answer this very question - and I don't remember the exact answer, but it was significantly more than half my weight (which is not so surprising: humans have a lot more mass in my head+torso than in their lower legs).
Apr
21
answered How to calculate displacement of an object
Apr
21
comment What are the best open-access journals in physics?
For a while, the regular APS journals would let you publish open access by paying an additional fee. As far as I know you can still do that, although maybe with the advent of PRX they'll discontinue that policy.
Apr
21
awarded  Critic
Apr
14
comment Are human eyes the best possible camera?
I disagree with the 10x worse than diffraction limit. You can do the experiment yourself: draw two closely spaced lines on a paper and see how far away you can get before you can't tell they're two lines anymore. I got (while wearing my glasses) an answer quite close to the diffraction limit. Heck, even the link you give claims that for people with good eyes it's within a factor of 2, not a factor of 10.
Apr
13
comment Why is it when you microwave cold coffee and then add milk it creates a foam head?
The coffee gods are punishing you for microwaving your coffee, which is one of the 7 deadly coffee sins.
Apr
12
comment Are smaller soap bubbles more accelerated by wind?
How the mass will scale depends on the size of the bubble. For a sufficiently large and thin bubble, the mass will be dominated by the enclosed air and scale as r^3.
Apr
11
answered Is spin is a conserved entity?
Apr
2
comment London penetration depth
Is this a trick question? Normally I associate the London penetration depth with the distance that magnetic fields penetrate the superconductor. With a type-2 superconductor, there's no Meissner effect. So what does London penetration depth mean in that context?
Mar
31
comment Recent breakthroughs in quantum computing?
I can't improve on the comment by Shor/Grosshans, but I don't think it's fair to restrict "major breakthrough" to "algorithms" alone. Another "major breakthroughs" are discoveries of how to do quantum error correction. Without some way of doing error correction, nobody's ever going to be able to implement large-scale calculations. And I think there have been significant improvements (on the theory side) in error correction techniques in the last 15 years.
Mar
27
comment Where's earths death bulge, destroying everything in it's path?
Continuing the above comment: The same Nature reference also quotes a tidal lag of the solid earth much smaller than the 2 hour lag you mentioned above. As for the water, long-wavelength water waves in an average-depth-of-4 km ocean would have a velocity of 200 m/s, so depending on how close you are to the equator, you could be drive above or below resonance. A perfect at-resonance drive would give a ~6 hour lag, so a 4 hour lag seems reasonable. The above two models would predict that most tidal dissipation on earth is coming from water (rather than rock).
Mar
27
comment Where's earths death bulge, destroying everything in it's path?
Shor: You are correct. I'll do some work to try to improve my comment. For the dynamics, I think it's a reasonable approximation to think of it as a damped harmonic oscillator. The equatorial surface velocity of the earth's rotation is ~500 m/s. The speed of sound in rock is something like 10 km/s, so the solid earth is driven far below resonance, hence there will only be a small (but nonzero) phase lag. The exact lag will depend on the damping, of course. But I think the damping is surprisingly low: Nature 381 p595 (1996) claims the Q of the tidally driven earth is around 370!
Mar
27
comment How would I go about detecting monopoles?
Yeah, it requires the monopole to go through the loop. That's a great way of distinguishing monopoles from dipoles. You can make the loop as big as you want, so I don't see how it would be an issue for a "macroscopic object". Unless you're using the word "macroscopic" in a different sense than I know it.
Mar
24
comment Comparing Energy Technologies in terms of: Cost per Power Capacity and Research Spendings
+1 for the Wikipedia link. Not only does it answer what I think is the more important question (which, as Roy Simpson pointed out, is the cost per MWh), but it also answers the original question asked regarding installation costs (although not the research cost).
Mar
24
answered How would I go about detecting monopoles?
Mar
24
comment Where's earths death bulge, destroying everything in it's path?
Just to elaborate on Prof. Shor's excellent answer: We notice the ocean tides because of the difference in the water and land bulge. This is due to both the different "stiffness" of water and rock, and also due to the different velocities of wave propagation. Because the tides drive the ocean above their resonant frequency, the tides lag the position of the sun/moon system by almost 90 degrees. Because sound propagates through the earth much faster, I think the earth tides are in phase with the position of the sun/moon.
Mar
24
answered What properties do you need for building a tower?
Mar
11
awarded  Commentator
Mar
11
comment Why is the decibel scale logarithmic?
@nibot Is it? My understanding is that dBc/Hz is typically used as a measure of phase noise. It's nonsensical as a measure of amplitude (or power) noise because I can't get the noise in dB by multiplying by the bandwidth in Hz (due to the logarithmic nature of the dB scale)
Mar
11
answered Why is the decibel scale logarithmic?