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Aug
20
comment Why is an Alcubierre drive shaped like it is
What is the difference between "contract space in front of you" vs "pancake space in front of you"?
Jul
31
comment Intro Mechanics: Finding ball speeds after collision
In real collisions, how does nature choose v1? If the collision is completely elastic, then both momentum and kinetic energy are conserved. Those two equations give a unique solution for the final v1 and v2. For a completely inelastic collision, momentum is conserved, but energy is not. However, we have one more piece of info - the masses are stuck together after the collision, so their final velocities are the same. This also gives us a unique solution. So, nature does not have any wiggle room to arbitrarily distribute momentum to one mass or the other - there is only one solution.
Jul
22
comment Is there a general rule for determining the direction of tension force?
@ja72 - Yes, that would be true for a rigid rod. But for homework-type problems, I think you can rule out compression for strings and ropes.
Jul
22
comment Is there a general rule for determining the direction of tension force?
No, the string never pushes the mass.
Jul
22
comment Is there a general rule for determining the direction of tension force?
Try it yourself - tie a string to a block, and grab the other end of the string with your hand. Now, try to use the string to move the block away from your hand. You can't, because the string goes limp. Now try to use the string to move the block towards your hand.
Jul
22
comment Is there a general rule for determining the direction of tension force?
Because the string "pulls" upward - if the force were pointing down, the string would be "pushing" the block.
Jul
22
comment Is there a general rule for determining the direction of tension force?
Here's an easy way to get it right, without worrying about "why": a string can only pull. If you try to push with a string, it will just fold up.
Jul
7
comment Radiation from home heaters
Are you asking whether the radiation from home heating units causes radioactive contamination to build up in your house?
Jul
1
comment Reduction of Earth's Rotation due to increase in humidity
But the atmosphere is not a rigid body. If the atmosphere rotates more slowly than the earth, then the earth's rotation might have to actually increase to conserve angular momentum.
Jun
25
comment How to design a stable table?
You need to define what constraints you want to place on the design. For example, a round tabletop with no leg and no base would be extremely stable. Or, if your base is larger than your tabletop, that will be extremely stable.
Jun
23
comment Good way to compute the force of a hammer blow?
What about pressure? Are you interested in measuring the difference between a hammer with a large striking area vs a hammer with a small area?
Jun
8
comment What is the voltage at every pair of points along a ideal wire that is connecting the two terminals of a battery?
For any segment of idealized wire, consider the voltage anywhere along the segment to be constant. In your game, you will need to separately handle the edge case where a wire shorts out a battery.
May
28
awarded  Yearling
May
27
awarded  Editor
May
27
revised Is there a huge difference between centrifugal and centripetal forces?
added 1 character in body
Apr
30
answered Is there a huge difference between centrifugal and centripetal forces?
Apr
29
comment Does a truck stop faster if the stack on the back of truck is stable or if it moves forward?
This analysis assumes that the moving haystack eventually stops due to friction. If instead the haystack stops due to colliding with the cab of the truck, does that change the answer? Also, would the timing of the collision matter (whether the haystack hits the cab before or after the truck comes to a stop)?
Mar
31
comment In circular motion, with a constant distance, why does the mass of the orbitting object have no effect on its revolution at all?
FYI - the orbiting object's mass does have an effect on the shape of the orbit. For example, if you increased the mass of the moon such that it had the same mass as the earth, the moon would no longer follow a circular path with the earth near its center. Instead, the moon and earth would both orbit around a point halfway between them. See barycentric coordinates.
Feb
16
comment Why does it take a projectile as long to get to its apex as it does to hit the ground?
This is probably the easiest way to explain it to someone in an intro to physics class, as long as you are able to convince the student that v(final) = -1 * v(initial).
Sep
24
comment Did the Big Bang happen at a point?
"The simple answer is that no, the Big Bang did not happen at a point. Instead it happened everywhere in the universe at the same time." By this, do you mean 1) that only the spacial dimensions were collapsed, but time was not, so the Bing Bang occurred at one moment in time, or 2) was all of spacetime collapsed, and the Big Bang occurred everywhere and every time.?