OT:Tempted to get this book

[Fyron]

narf poit chez BOOM said:
Excuse me, but if I push on a block of wood and you push on a block of wood and we both have equal strength, given your arguement, neither of us would be expending energy. However, I think in half an hour you would say otherwise, no mater how balanced the forces are.

Erm... the difference is that the refridgerator expends 0 energy to hold the magnet in place. The point was that not _all_ stationary objects require energy to remain stationary. Certainly, you can waste energy on an object that doesn't move in the end, but that is not the same thing. When pushing a block that isn't moving, you are not transfering any energy to it. The force you apply is not enough to overcome the counterforces involved, so no work is done on the block. As a result, its energy does not change. You have used energy, but that is for an entirely different reason. It requires a constant source of energy to keep your muscles contracted.

[narf poit chez BOOM]

But what's keeping the block from moving?

[Fyron]

The total net force on the block is 0. The force of gravity is balanced by the "normal force" that the ground applies back to the block (equal magnitude but exactly opposing direction). The force that person A exerts on the block is exactly the same in magnitude as the force that person B exerts on the block, but in the opposite direction. Note that Force = Mass X Acceleration. If there is no net force, there is no acceleration, thus no change in velocity. Since the initial velocity of the block was 0, it remains 0.

[narf poit chez BOOM]

I submit that the persons squeezing from either end are not directly opposing each other, but are each contracting the block miniscully(sp?), causing it's molecular bonds to contract into a slightly uncomfortable range and exert a countering force.

And even if that's complete blather, my point still stands, that force cannot be exerted without energy.

[narf poit chez BOOM]

If light has mass and goes at lightspeed, how come we're not all squished?
Best answer I can think of is that light ignores that rule and simply exerts force according to it's mass. What that might mean, I don't know.

[Jack Simth]

narf poit chez BOOM said:
If light has mass and goes at lightspeed, how come we're not all squished?
Best answer I can think of is that light ignores that rule and simply exerts force according to it's mass. What that might mean, I don't know.

It's been a while since I've taken physics but ....
Light has 0 rest mass, and thus 0 rest energy. However, it travels at the speed of light. The equation for the energy (mass, energy; essentially the same thing in modern physics) of an object is something like E = sqrt(1/(1-(v^2/c^2)))mc^2. For light, m = 0, but v = c. The equation then translates to
E = sqrt(1/(1-(c^2/c^2)))(0)c^2
= sqrt(1/(1-1))(0)
= sqrt(1/0)(0)
= (1/0)(0)
= (0/0)
Which is mathamatically undefined. However, the universe comes up with an answer! It's a particular constant over the wavelength of the light, for any given photon (there's something similar for the inertia of the photon). Fortunately, it's a VERY SMALL constant, so it takes a LOT of photons to have any measureable impact when they hit you.

[narf poit chez BOOM]

If light has 0 rest mass and 0 mass from lightspeed, how can it have any mass at all?