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May
12
comment Is true black possible?
To make an even better black, although not stricly speaking a black surface: make a box, cover it with this fabric on the inside, and leave a hole in the box. The hole will be more black than the material itself.
Apr
26
comment Can you ever exert more downwards force than your weight?
Run an experiment. Stand on the scales, then jump. Scales measure the force with which you push down. When you jump, the arrow will shoot up and exceed your weight, proving that it's possible. Disclaimer: use cheap scales in case you damage them.
Apr
16
comment Why doesn't light, which travels faster than sound, produce a sonic boom?
At first I also thought "Cherenkov radiation", but this question is asking why light doesn't make a sonic boom, not why there is no equivalent of a sonic boom when it comes to light.
Apr
16
comment Potential energy of Hydroelectric plant before the dam was built
Could the energy extracted by the plant have actually been reaching the river's drain before, and getting dumped into whatever sea/lake/ocean it terminates in? It would be nice to see a reference confirming that the properties of the water flow at the drain (volume/speed/temperature) are not changed significantly by building a plant 100km upstream.
Apr
16
comment Energy Analysis of Niagara Falls in Linus Pauling's “General Chemistry”
One other thing not accounted for by the simple potential energy calculation is that the water might well be reaching terminal velocity for a given droplet size, thus losing some energy by heating the air.
Apr
8
comment Determining the refractive index of a foil
Thanks for the warning. Mine says 405nm on it, and was actually sold as a UV laser, <10 mW. It looks violet when it hits most surfaces, but paper fluoresces rather brightly in a different shade. I do rather hope they don't become illegal. Motorcycles are vastly more dangerous and they're legal!
Apr
8
comment Determining the refractive index of a foil
Crappy blue lasers are no longer expensive: amzn.com/B00J7IFESY
Apr
7
awarded  Yearling
Apr
7
revised Why dark matter and general relativity?
added 325 characters in body
Apr
7
answered Why dark matter and general relativity?
Apr
5
comment Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?
@ChrisMueller yes, it does; the green dots are very close together compared to the angular distance between the green and the red or blue.
Apr
3
awarded  Nice Question
Apr
2
answered What exactly is fire?
Apr
2
comment Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?
Thanks! The equal spacing between the three dots didn't seem accidental, and this answer explains well why they're equal. With this new keyword I found this video (note, it's a download) showing the spectrum of a laser as the current is increased. It shows multiple peaks at some currents and a single peak at others – fascinating!
Apr
2
accepted Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?
Apr
1
asked Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?
Feb
12
comment What happens before a radioactive element decays?
@RenéNyffenegger your best bet is to get used to the idea that "random" is scientific. It's a very precise kind of "random". Randomness can be highly scientific, and an entire branch of mathematics is dedicated to drawing accurate conclusions about "random" things.
Feb
2
comment Is there a small enough planet or asteroid you can orbit by jumping?
"though I wouldn't like approaching a planet with high speed" — but if you ran/jumped to start on your orbit, then that's how fast you'll touch back down, so it's not like you'll actually be moving at a very high speed upon touchdown. It's physically impossible to end up moving faster than that if the surface is a perfect sphere.
Feb
2
comment Why $F=ma$ and not $F=m\dot{a}$?
This could be asked about any law of our universe. Now, some of them can be derived from more general ones, but for now the best answer available is "because that's the formula that matches observation" and "we don't know what ultimately made our universe the way it is".
Aug
30
comment Can a human size object move so fast that it ceases to be observable?
@Jim What do you care whether we say "yes" or "no"? We all agree that the photons will be reflected and that they are observable. THAT is what matters here. Whether you call it a "yes" or a "no" is irrelevant. Some answers like to go beyond that and contemplate whether a human can spot these photons without specialized equipment, that's all.