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Jan
17
comment How am I able to stand up and walk down the aisle of a flying passenger jet?
This does not seem to answer the question in any meaningful sense.
Dec
28
comment Why is there an electric field in a wire even though it is a conductor?
@1110101001: The fact that some current/voltage source (e.g. a battery, a generator, etc.) is constantly moving electrons the other way, and thus replenishing the field as fast as it decays. Disconnect the source, and the field does disappear very quickly (limited only by the resistance of the wire).
Dec
25
comment Do raindrops spin as they fall?
True, that part of your answer is correct -- the shape of a raindrop is not the one with minimum drag among all possible shaped. (It also doesn't seem to have anything to do with the question, but it is correct.)
Dec
25
comment Do raindrops spin as they fall?
Raindrops are not actually "teardrop-shaped", and do not have a tapered tail. This is just a common myth. The actual shape of a falling raindrop is a slightly flattened sphere, not entirely unlike, say, a round bread roll.
Dec
5
comment In terms of forces and kinematics, why does a projectile, thrown forwards, bounce forwards?
Note that, if the ball is spinning fast enough when it hits the ground, it can bounce backwards. That's probably not the case you're asking about, but I just wanted to point out that the direction of the bounce depends on both the velocity and the rotation of the ball. You can't treat those as independent, unless you want to neglect friction completely.
Nov
19
comment Could we launch a missile from a planet with the mass of Jupiter?
Note that a planet with the radius of Earth and the mass of Jupiter would have a mean density of $1.7 \times 10^6\,{\rm kg/m^3}$. That's over 75 times the density of solid osmium, making such a planet pretty much physically impossible. (White dwarfs and neutron stars achieve far higher densities, around $10^9\,{\rm kg/m^3}$ and above, but there doesn't seem to be any way to have a planetary-size body with a density like your calculations imply.) A (slightly) more reasonable scenario might be a Jupiter-mass planet with the same density as Earth.
Nov
17
comment Why can't I see the blue color scattered by the lower atmosphere of the earth?
You sure you can't? You may just need to be in the right place (clear dry air + distant backdrop = mountains, typically) to notice it clearly.
Oct
28
comment If UV radiation 1 cm away from the halogen bulb is equal to Sun's radiation, what is the level of radiation 1 meter away?
Good point, a 1 cm filament at a distance of 1 cm is in the transition region where neither 1/r nor 1/r² is a very good approximation of the falloff. But still, the range from 1 cm to 1 m lies mostly in the 1/r² region, so the intensity at 1 m will be about 1/10,000 = 0.01% of the intensity at 1 cm. It certainly won't be anywhere near 1/100 = 1%.
Oct
27
comment If UV radiation 1 cm away from the halogen bulb is equal to Sun's radiation, what is the level of radiation 1 meter away?
The $1/r$ falloff applies to a long cylinder (i.e. one significantly longer than your distance from it). A light bulb filament, at distances of over $1\,{\rm cm}$, is well approximated by a point source (i.e. the $1/r^2$ falloff rule applies).
Oct
19
comment Will the box move?
If the surface is not frictionless, it's possible to obtain a non-zero net velocity using method 3. In fact, an even better method would likely be for the man to repeatedly walk from one end of the box to the other, and run back. Or just stand in place and shift his weight back and forth, slowly in one direction and quickly in the other.
Sep
8
comment Do solar systems typically spin in the same direction as their galaxy?
"note, the solar system is not drawn to scale compared with the Galaxy" ...or compared with itself, for that matter.
Aug
17
comment What does it mean if a = g in this situation?
Alas, it looks like ImageShack has deleted your image, and replaced it with an ad banner. If you can, please reupload the image (or something equivalent) using the image upload button in the editor toolbar (which will upload it to Stack Exchange's imgur account).
Aug
13
comment Can a Skydiver Land On a Large Slide and Survive?
See also: ski jumping.
Aug
2
comment What is the smallest distance possible between two stars?
en.wikipedia.org/wiki/Contact_binary
Jul
30
comment Conical train wheels
Also, I'm pretty sure the center-of-mass argument is backwards. It really doesn't matter whether the CoM moves left or right; what matters for stability is whether it moves up or down, and that's not so obvious from the geometry. (In particular, it depends on the curvature of the wheel surfaces, not just on their slope.) But, of course, the wheel radius effect described by @Kyle probably dominates this anyway.
Apr
29
comment Does a truck stop faster if the stack on the back of truck is stable or if it moves forward?
Short answer: If the stack slides, the truck will stop faster, but the stack will stop slower. Depending on what the stack consist of, that may or may not be desirable.
Apr
24
comment Paradox in applying Newton's second law
Why the hidden spoilers?
Apr
1
comment Why doesn't light affect a compass?
Technically, light does cause (bits of) the needle (mostly, the electrons) to wiggle at around 400-800 THz, which is why we can see it in the first place. If it didn't interact with visible light at all, it would be totally transparent.
Mar
2
comment Why doesn't a cigarette lighter generate thrust?
The combustion will also generate some minimal thrust, since it will heat the gas, causing it to expand, and some of that expanding gas will push against the lighter. Still, the combustion geometry is very poor (and the amount of fuel minimal anyway), so you won't get much thrust out of it.
Jan
21
comment Is there a thermodynamic limit on how efficiently you can solve a Rubik's cube?
@MarkEichenlaub: The scrambled cube has about $2^{65}$ possible states; the solved one has only one. On the microscopic level, physics is reversible, so when the cube is solved, the information needed to reverse the solution and reconstruct the original scrambled state from the solved one must go somewhere. That means it either has to be stored in some part of the system, or emitted from it (as heat).