OT: The 10th Demention

[Spoo]

Raapys said:
If you pick up a box and hold it for one hour then you've spent alot more energy than if you merly lift it up and drop it at once. Yet, the box doesn't have any more energy when it falls after one hour than it does if you release it instantly. So where did the energy you continously applied to the box for one hour go?

Your muscles require a constant use of energy to remain contracted. That energy ultimately "goes" into heating your body over the course of the hour that you spent holding the box.

[Raapys]

But you're keeping your muscles contracted *to keep the thing from falling to the ground*, thus you are, for that entire hour, applying more and more kinetic energy to the box. Put it like this: if the gravity was to suddenly vanish, the box would go flying off from the force you were exerting on it at that given moment. You're not exerting any less force on it just because it's not moving.

[Suicide Junkie]

It would drift off very slowly.

It starts at rest relative to you and the surface of the Earth, and you will be pushing 9.8m/s^2 for maybe 1/10th of a second before you notice and stop pushing.

You aren't actually adding any kinetic energy to the box.
Work = force * distance.

Effort feels more like force * time, but it dosen't have any serious meaning.

[Raapys]

But the 'work = force * distance' function is fatally flawed when used in this situation, because the result of the equation will be zero, indicating no energy has been spent, no work has been done. Obviously this is completely incorrect, since you'll be standing there sweaty and tired, having wasted alot of energy on the task.

I think a fitting metaphor would be two guys pulling each side of a rope. They're both applying kinetic energy to the rope, but in different directions, canceling it out. So even if the rope isn't actually moving, there's still alot of work being done on it. The difference is that where both these two guys would eventually get tired, gravity does not.

Hmm, I guess one solution would be that the force you're using to hold the box up is simply being applied as kinetic energy to the *Earth*, thus seemingly 'disappearing' since it's hardly noticeable for something on that scale.

[se5a]

they're not applying kinetic engergy, it would be... burning organic matter and turning it into heat mostly.
I think...

[Spoo]

Raapys said:
But the 'work = force * distance' function is fatally flawed when used in this situation, because the result of the equation will be zero, indicating no energy has been spent, no work has been done. Obviously this is completely incorrect, since you'll be standing there sweaty and tired, having wasted alot of energy on the task.

Work is being done in the sense that ions are being moved around in your muscle cells to keep the muscle contracted.

I think a fitting metaphor would be two guys pulling each side of a rope. They're both applying kinetic energy to the rope, but in different directions, canceling it out. So even if the rope isn't actually moving, there's still alot of work being done on it. The difference is that where both these two guys would eventually get tired, gravity does not.

The rope isn't moving, thus it has no kinetic energy. Likewise, no work is done on the rope (although the two guys will grow tired because work is being done within their muscle cells).

[Raapys]

Work is being done in the sense that ions are being moved around in your muscle cells to keep the muscle contracted.

Yes, to the same degree that it's being done when you're actually moving something. But where does the energy that you use to move something go when you're not strong enough to move it? Or when you're using the same power that you used to move something to just fight gravity?

The rope isn't moving, thus it has no kinetic energy. Likewise, no work is done on the rope (although the two guys will grow tired because work is being done within their muscle cells).

The rope isn't moving, true, and thus it has no kinetic energy. However, it *is* being applied kinetic energy; it's just that it's being applied the same amount of energy pulled in opposite directions, thus canceling out. *Obviously* work is being done on the rope, because if they both pull hard enough, after all, they could rip it in two. Yet using the, in this case faulty, work = force * distance equation, you'll still get 'zero work has been done' even if you have ripped it in two and applied massive forces on the rope to do it. The equation is useless for these sorts of scenarios, since it requires that a distance has been covered to get a non-zero result.

Let's say we invented kinetic energy weapons. They shoot a small amount of pure kinetic energy. We're in space, and there's a metal cube or whatever floating directly between two ships which have these weapons mounted. They're at the same distance from the cube, etc. Then, at the exact same moment, both of them fire their weapon at this object. The weapon applies the energy to the entire cube at the same instant.

What happens?