5,151 reputation
1127
bio website keith-s-thompson.github.com
location San Diego, CA
age 54
visits member for 2 years, 6 months
seen yesterday

I'm a programmer and all-around nerd living in San Diego, California and working at JetHead Development Inc.

E-mail: Keith.S.Thompson@gmail.com


Apr
21
awarded  Nice Answer
Apr
15
awarded  Necromancer
Apr
3
revised Is Feynman's explanation of how the moon stays in orbit wrong?
added 470 characters in body
Mar
31
comment What cosmic event would cause Sun rising from the west?
A collision sufficient to reverse the Earth's rotation wouldn't just melt the surface it would disrupt the planet and create a new asteroid belt. (Quite possibly I'm wrong; feel free to do the math.)
Mar
31
comment What cosmic event would cause Sun rising from the west?
"In principle the tidal forces of the Sun will eventually slow the Earth's rotation so it always shows the same face to the Sun." -- Only given certain carefully chosen principles which ignore the existence of the Moon. The Moon's much stronger tides will eventually cause the Earth's rotation to become tidally locked to the Moon, not to the Sun. (Assuming our descendants or successors don't do something about it in the meantime.)
Mar
31
comment Is Feynman's explanation of how the moon stays in orbit wrong?
@mtanti: If you stay in the original frame of reference, the distance the ball moves "down" is larger. But the Earth is no longer straight "down"; it's now below and a little bit "behind" the Moon's new position. Over a short time span, the Moon's motion approximates the parabola it would follow in a uniform gravitational field; the Earth is at the center of the circle that's tangent to that parabola.
Mar
30
comment Is Feynman's explanation of how the moon stays in orbit wrong?
@MarkMitchison: Good point, I've updated my answer accordingly.
Mar
30
revised Is Feynman's explanation of how the moon stays in orbit wrong?
added 48 characters in body
Mar
30
answered Is Feynman's explanation of how the moon stays in orbit wrong?
Mar
18
revised How does space affect the human body (no space suit, no space craft)
Link to YouTube video
Feb
27
comment What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?
If you have a tall glass of water with a given fixed surface area, it will lose a constant amount of water per unit of time (in an identical environment); the deeper the water, the longer it will last. But for a given volume, the large the surface area that's exposed to air, the more quickly it will evaporate.
Feb
26
comment What's the surface area of a liquid? How does evaporation increase if the surface area of a liquid is increased?
Why would having more surface molecules make the evaporation rate decrease?
Feb
26
comment Density of stars near the center of the Milky Way
@theJollySin: Not really. I've updated my answer with a link to a Wikipedia article that gives different figures.
Feb
26
revised Density of stars near the center of the Milky Way
Link is dead, add another
Feb
17
comment Stresses in asteroid during close flyby
Tide is the difference in (gravitational) acceleration over distance. It falls off with the cube of the distance from the primary, which is why the Moon's tidal effect on the Earth is stronger than the Sun's. For an asteroid near Earth, the (differential) force from the tide and the asteroid's own gravitational cohesion are both fairly small; within Roche's limit, the tide exceed's the asteroid's gravity. The net gravitational force on the asteroid is zero, since it's in free fall, so I don't think "jerk" comes into it, except perhaps as a second or third order effect.
Feb
16
revised Stresses in asteroid during close flyby
added 60 characters in body
Feb
16
answered Stresses in asteroid during close flyby
Feb
15
comment Is the moon a planet?
If we discovered, say, a Neptune-sized body in a nearly circular orbit at 150 AUs, I think we should call it a "planet". And we've detected hundreds of "planets" orbiting other stars. If we're going to use the word, I think we should have a consistent definition for it.
Feb
12
awarded  Good Answer
Jan
28
comment Is it possible for a physical object to have a irrational length?
Every object's length is rational if you use its own length as the unit of measurement. 8-)}