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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
26
awarded  Nice Answer
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.
Oct
3
revised Two planets in same orbit - not planets?
fix broken image link
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
revised How to make the projected image smaller by adding one ore more lenses in front of the built in projector lense?
reupload image from imageshack to stack.imgur before it gets replaced by ads; see http://meta.stackexchange.com/q/263771
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
17
revised Why does air contain $Ar$ specifically?
remove broken ImageShack image
Aug
17
revised $t\bar{t}$ asymmetry
reupload image from imageshack to stack.imgur before it gets replaced by ads; see http://meta.stackexchange.com/q/263771
Aug
17
revised ATLAS and CMS calorimeters
reupload image from imageshack to stack.imgur before it gets replaced by ads; see http://meta.stackexchange.com/q/263771
Aug
17
revised Is there a way to fill Tank 2 from Tank 1 through Gravity alone?
reupload image from imageshack to stack.imgur before it gets replaced by ads; see http://meta.stackexchange.com/q/263771
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.
Jul
23
awarded  Yearling
Jul
15
awarded  Nice Answer
Jul
14
revised Why are expressions such as $\operatorname{ln}T$ used in thermodynamics where $T$ is not dimensionless?
copy comments into answer
Jul
12
answered Why does medium not affect the frequency of sound?
May
13
answered What will happen if a ball of ice with the mass of sun is thrown into the sun?