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[miauw62]

This instantly came to mind when i heard this question.

[da_nang]

Hyperphysics, to the rescue!

[i2amroy]

I wonder if you could use Earth's gravity at the center to power a generator? Something like a gyroscope.

No.  Although there'd be a huge amount of geothermal energy available if you made a deep hole.

Leafsnails correct here. Earth's gravity can't be used as a generator because all it does is pull, meaning that any conversion of energy you do with gravity has no way of reversing the polarity to reset itself.

If you were looking to harness the planet's rotational energy, then the source you would want to tap into would be earth's magnetic field, which is caused by the molten core rotating.

[TSTwizby]

And if you meant to harness energy by dropping something and having it push a turbine or something like that as it oscillates, then while you would get a fair amount of energy out of the deal (a maximum of about 30 megajoules of energy per kilogram dropped, ignoring efficiency considerations) the object would have less energy and thus rise less far each time it passed through the core, eventually coming to rest in the center (and clogging up your machine most likely) after the maximum energy is harvested.

[Karlito]

We can use the Moon's gravity for electricity generation.

[10ebbor10]

We can use the Moon's gravity for electricity generation.

That's using the Moon's rotational energy. The gravity is just a way to convey the power to the water.

[TSTwizby]

Specifically, the energy of the motion of the moon around the earth, as opposed to the motion of the moon itself spinning in place. Which it doesn't do, hence the whole 'dark side of the moon' thing.

[LARD]

One more problem to consider in this equation is whether or not there is a terminal velocity in a vacuum. I believe terminal velocity is just when the object is held at a certain speed by the air resistance so it wouldn't be a problem in this scenario.

If I may quote myself

(this is assuming completely perfect circumstances)

But that's fine, you can see how many reasons you can find for this not being possible. I find them interesting.

[kaijyuu]

There is no terminal velocity in a (perfect) vacuum. Terminal velocity is when the acceleration and the drag from friction become equal. Zero drag = infinite terminal velocity.

In a fantasy environment with constant gravity, an object would speed up indefinitely and approach c.

[i2amroy]

One more problem to consider in this equation is whether or not there is a terminal velocity in a vacuum. I believe terminal velocity is just when the object is held at a certain speed by the air resistance so it wouldn't be a problem in this scenario.

Terminal velocity is based off air resistance. In a perfect vacuum the only limit you have on what speed you can go (assuming gentle acceleration) is the speed of light itself.

Edit: Dang Ninja!

[Snowblind]

Well, I wonder if you dropped the ball down the shaft if it would build enough momentum to shoot clear out the other side, achieve escape velocity?

Probably not.

[Graknorke]

Well, I wonder if you dropped the ball down the shaft if it would build enough momentum to shoot clear out the other side, achieve escape velocity?

Probably not.

No it wouldn't.
It would peak at the equivalent height of where you dropped it from.

[Leafsnail]

"You can't create energy" is a good thing to remember when coming up with zany energy producing ideas.  You can certainly harness energy, but it has to come from somewhere.

[TSTwizby]

There is no terminal velocity in a (perfect) vacuum. Terminal velocity is when the acceleration and the drag from friction become equal. Zero drag = infinite terminal velocity.

In a fantasy environment with constant gravity, an object would speed up indefinitely and approach c.

Just making sure it's said, the force of gravity inside the earth is not constant, but instead decreases roughly with the cube of the distance from the center of the earth.

edit: sorry, correction: the force of gravity varies with the actual distance, not the cube. I forgot to divide by r^2...

[Neonivek]

Zero drag = infinite terminal velocity

I cannot remember the exact force that prevents this.