428 reputation
210
bio website
location
age
visits member for 2 years, 6 months
seen Aug 18 at 18:03

May
15
comment Any liquid metallic alloys which are safe to handle with bare hands?
I suppose, while not a true alloy, ferrofluid (ask.metafilter.com/145880/Ferro-fluid-experiment-safe) is relatively harmless and has several metallic properties...
Dec
19
comment How to smooth the spectrum of a light source?
Direction, partially (more to keep the intensity high enough to be usable than, say, to do imaging). Doesn't a tunable laser have just a few lines, one/some of which can be selected?
Sep
17
comment Why planes have propellers in front but watercraft have them behind?
Thanks, AlanSE. That's insightful information. About stability, does that make vehicles with back-mounted propellers oversteer, and front ones understeer, as back and front-wheel-drive cars do?
Apr
30
comment Gravitational potential outside Lagrangian points or Lagrange points
Thanks a lot, AlanSE. That explains it very well. +1 for explaining the equation too!
Apr
30
comment Gravitational potential outside Lagrangian points or Lagrange points
It was from csep10.phys.utk.edu/astr162/lect/binaries/accreting.html seemingly from a University of Tennessee lecture. The accompanying text states specifically, "The gravitational potential energy for a binary system is plotted in the adjacent diagram."
Apr
18
comment Why there is no “Edison” unit in physics?
And he had 2 units named after him: sizes.com/units/siemens.htm
Apr
8
comment Gravitational potential outside Lagrangian points or Lagrange points
Thanks for the explanation. I'm not much concerned about the stability at L4 or L5, but rather the implications on movement far away. The surface slopes downwards (in fact at an increasing rate) far from the ring. Does that mean that a free body there will move away from the masses?
Oct
1
comment Store up cheap electricity to use later?
Likely. Perhaps you could look into other ways of cooling your home instead, such as setting up sun shades or atomising water in front of a fan: yardsurfer.com/outdoor-misting-fan
Sep
29
comment Store up cheap electricity to use later?
@zephyr: Not necessarily true; there are many reasons why a company may not go into a certain line of business. As the Wikipedia link shows some companies do do that, it not only shows theoretical possibility but actual viability.
Sep
27
comment Underground explosions due to plate tectonics and natural gas pockets
It's likely that parts undergoing subduction i.e. active regions at the fringes of the tectonic plates don't have enough time to build up substantial reserves of oil or gas. It's the stable areas far from plate boundaries that manage to build up reserves over time.
Sep
26
comment How does nuclear war look like from space?
@Martin: Brilliant :-D
Apr
14
comment What do bullet trails really look like?
Thanks, dmckee. It's interesting that your images (presumably) show subsonic bullets whereas tmac's are supersonic. I wonder what differences that makes.
Apr
14
comment What do bullet trails really look like?
Thanks for clarifying, tmac. That's what I expected. I wonder if you could comment on dmckee's answer below. In his images, I presume air rifle bullets are subsonic. Should any distortion be visible for bullets travelling below the speed of sound?
Apr
12
comment What do bullet trails really look like?
Thanks, tmac. Based on your images and assuming supersonic bullets, am I correct to conclude that the main effects are (1) a small cloud just behind the bullet and (2) a blunt refracting cone shell just ahead of it? From equation BoatSpeed = WaveSpeed x tan(PI/2-Angle) at physicsforums.com/showthread.php?t=328445, is it right that the cone's half-angle is PI/2 - atan(Mach number) i.e. 39 degrees for 1380 ft/s bullets from Desert Eagles that Agents use? It's unclear from the shadowgraph how far the cone extends or how visible it is to the naked eye. Any idea? What about subsonic bullets?
Apr
12
comment What do bullet trails really look like?
Could you please explain "a non-trivial stretch of space before the bullet's point of impact?" Perhaps my question was unclear: I wish to know what a bullet trail looks like as it is flying through air, not after it has hit a solid or liquid object. In your examples, most of the particles are debris from the target.