South Pole Axis

If one constructed a platform at the absolute south pole, that is truly perpendicular to the earths axis and then constructed a shaft on such platform that is aligned parallel and on center with the earths south pole axis and then installed a bearing, with large weights on the outer circumference of such bearing, onto such a shaft, would such a bearing not spin as the earth rotates? If such is true, then couldn't a gear be fixed to the top of the bearing that would cause other gears attached to earth to rotate as the earth rotates. Thus giving one the ability to generate energy?

Answers and Replies

All you said could be done except for the part of generating energy

mfb
Mentor
It would rotate together with earth, so relative to the ground it would not spin.

To extract energy, you would need some external anchor - which you do not have.

How couldn't you tap into the rotation of the gears shaft that is installed through a bearing, attached to an arm or some other structure fixed to earth.

Bandersnatch
Science Advisor
Hi MatLepine, welcome to PF!

No, it wouldn't work. For the contraption to work, you'd need some elements to rotate at a different angular velocity than others. That is to say, the outer weights would have to complete the rotation around the central shaft either faster or slower than the shaft itself.

All parts of Eath have the same angular velocity(360°/day) w/r to the axis or rotation, though.
The somewhat counterituitive physics to understand here is the Newton's first law of motion for rotation, which states that in the absence of external torque(i.e., forces changing rotation) the rotating body will either not rotate, or rotate at a constant angular velocity, forever.
In everyday life we're used to thinking that rotation requires a force to maintain. Windmills need wind to keep working, ice skaters eventually slow down in their piruettes, etc. In all those cases there's a force(friction) acting against rotation.
With Earth, there is no such force, at least not on the scale useful for energy extraction(there are tidal forces, but that's another kettle of fish).

What one could try to do, I suppose, is use the Coriolis force(http://en.wikipedia.org/wiki/Coriolis_effect#Applied_to_Earth), for example by swinging a giant pendulum in a vacuum chamber, and somehow extracting the energy as it gets deflected.

The weights on the bearings outer circumference should act as an anchor. The bearing would prevent the transfer of energy from the shaft to the weights, right?

Bandersnatch
Science Advisor
No, you would need an anchor outside Earth.

So where would the weights get the energy to rotate with the earth, if they are attached to the outside of the bearing? I don't see how the energy from the shaft would apply directly to the weights.

mfb
Mentor
What one could try to do, I suppose, is use the Coriolis force(http://en.wikipedia.org/wiki/Coriolis_effect#Applied_to_Earth), for example by swinging a giant pendulum in a vacuum chamber, and somehow extracting the energy as it gets deflected.
That does not help, you get (at most) the energy you put in to make it swing.

There is one way to extract energy out of the rotation: build a space elevator, and extend it sufficiently (something like ~100,000km if I remember correctly). Lift masses up - the first 36000km will cost energy (as the gravitational attraction dominates), but everything beyond that will give you energy back (centrifugal force dominates). You can even use this to launch objects into our solar system.
This is not practical as a power plant due to the low power output, but it is at least a theoretical possibility.

256bits
Gold Member
Hey Matt
Great idea.
But with a catch as other have said.
If you look at any motor, transmission, generator you will see a rotating shaft(s) and a non-rotating housing.
The shaft(s) has to rotate with respect to something else.
If the housing is not tied down, it will begin to rotate in the same direction as the shaft.

So if your weights connect to the housing, they would need to be non-rotating wrt the earth.

you have 2 ways to do this.
1. Bring all the weights to the south pole, and then move them quickly radially out to the end of the arms. For a short while you can extract some energy, but the weights will eventually end up revolving in step in the same directions as the the earth.
To bring the weights back in to the centre to start anew you would have to overcome the centripital force of the weights, and to do that requires energy.

2. You could assemble a system to keep the arms non-rotating ( by looking down onto the south pole from space you would see the earth revolving and the arms also, so you want the arms non-rotating or at a different rate than that of the earth ) One way to do this would be to round up a bunch of South American penguins, hook them up to the arm and have them walk against the earth's rotation. But you could just as well have them walk in the same direction as the earth's rotation. In both cases you would be extracting Penguin Power, much like a donkey walks around in a circle on a pole using Donkey Power and the friction of its hoofs against the ground to turn the gristmill for making flour,

SteamKing
Staff Emeritus
Science Advisor
Homework Helper
It doesn't work for the same reason that putting a tire on the ground on the equator doesn't start to spin on its own as the earth turns. All of these things are attracted to the earth by gravity (like the atmosphere) and they turn with the earth as it rotates.

I was thinking more of using fixed weights. I was also thinking that as the energy from the gears start to transfer to the weights, which will cause the weights to rotate, you could use the same gears as a breaking mechanism and absorb energy like that?

I thank you guys for your input. I may sound naive to you, as I am in this area, so I appreciate you taking the time.

SteamKing
Staff Emeritus
Science Advisor
Homework Helper
I was thinking more of using fixed weights. I was also thinking that as the energy from the gears start to transfer to the weights, which will cause the weights to rotate, you could use the same gears as a breaking mechanism and absorb energy like that?

It's 'braking' mechanism.

Again, the gears or whatnot are all gravitationally bound to the earth. They will spin along with the earth. That's why you are not thrown off your feet when you stand up. You, your mom, your dog, your car, and your house are all gravitationally bound to the earth, even at the south pole, which, by the way, has no pole there.