Free Energy from the Earth's Rotation

[Dale]

The diference between a tree and a electrical generating windmill though is the windmill converts the energy into heat, which can escape the Earths atmosphere into space, where it came from in the first place, via the sun.

As A.T. mentioned this is not a difference. Turbulence and drag converts KE in the fluid to thermal energy. Furthermore, that is relevant to energy, not angular momentum. You again appear to be confusing energy and angular momentum.

This is very simple. If windmills slowed down the Earth's rotation then they would be taking net angular momentum out of the ground, since angular momentum is conserved the windmills would have to put that angular momentum into the air. In order for the air to hold that angular momentum it would have to spin faster. This would mean a steady change in the global mean wind velocity in the direction of rotation which is proportional to the amount of wind power being generated globally. Since we don't observe that we can conclude that angular momentum is not being drawn out by windmills.

 

[Buckleymanor]

That is not a difference, but something that happens in both cases:

- The tree converts the kinetic energy into turbulence which ends up as heat.
- The windmill converts the kinetic energy into electricity which ends up as heat.


The heat generated by the tree from wind also leaves the Earth+atmosphere system through radiation.

So what you are saying is a tree blowing in the wind which has evolved converts kinetic energy into heat as efficiently as a wind generator which has been designed whith that in purpose to do so.

 

[Buckleymanor]

Angular momentum and rotational kinetic energy are different things. You've been told this many times now. Do you understand the distinction? Can you tell us what the distinction is?

One is the amount of momentum a rotateing object has (angular)and the other is the total amount of kinetic energy a rotateing object has.

 

[Buckleymanor]

As A.T. mentioned this is not a difference. Turbulence and drag converts KE in the fluid to thermal energy. Furthermore, that is relevant to energy, not angular momentum. You again appear to be confusing energy and angular momentum.

This is very simple. If windmills slowed down the Earth's rotation then they would be taking net angular momentum out of the ground, since angular momentum is conserved the windmills would have to put that angular momentum into the air. In order for the air to hold that angular momentum it would have to spin faster. This would mean a steady change in the global mean wind velocity in the direction of rotation which is proportional to the amount of wind power being generated globally. Since we don't observe that we can conclude that angular momentum is not being drawn out by windmills.

It does look that way I failed to add that trees produce heat via turbulance though it did cross my mind at the time. The point remains that they do not do that as efficeintly as a turbine which was why this was not mentioned.

 

[jbriggs444]

One is the amount of momentum a rotateing object has (angular)and the other is the total amount of kinetic energy a rotateing object has.

Saying that angular momentum is the amount of momentum that a rotating object has (angular) is not an adequate characterization of angular momentum.

Saying that rotational kinetic energy is the total amount of kinetic energy a rotating object has is outright incorrect.

 

[A.T.]

So what you are saying is a tree blowing in the wind which has evolved converts kinetic energy into heat as efficiently as a wind generator which has been designed whith that in purpose to do so.

Windmills are not designed to covert kinetic energy into heat, but into electrical energy. They do convert some of the KE into heat, which is considered an inefficiency.

But using your inverted idea of "efficiency", a tree is far more "efficient" in converting KE into heat, because it converts all of the KE it takes from the wind into heat, not just some of it like a windmill.

The point remains that they do not do that as efficeintly as a turbine which was why this was not mentioned.

Please define precisely what you mean by "efficiency" here. And explain how it is relevant to the topic, which is reducing the Earth's rotational KE to generate usable power with an Earth bound device.

 

[Buckleymanor]

Windmills are not designed to covert kinetic energy into heat, but into electrical energy. They do convert some of the KE into heat, which is considered an inefficiency.

But using your inverted idea of "efficiency", a tree is far more "efficient" in converting KE into heat, because it converts all of the KE it takes from the wind into heat, not just some of it like a windmill.



Please define precisely what you mean by "efficiency" here. And explain how it is relevant to the topic, which is reducing the Earth's rotational KE to generate usable power with an Earth bound device.

The difference between the amount of KE converted into heat over time.
A tree might well convert all of the KE it takes from the wind into heat and a windmill is designed to make electrical energy which ends up through use also into heat.
So the tree is more efficeint at produceing heat (converting KE into heat) though the amount of heat a 15M high tree produces is a lot less than a 60M windmill over the same period.
So the more windmills built the more KE taken from the Earth's rotation and turned into heat which is lost in space.
An albatros can probably convert fish into flight more efficiently(or heat) than a jumbo jet can turn aviation fuel into flight or heat.The jumbo though uses a lot more fuel and produces a lot more heat crossing the atlantic.

 

[jbriggs444]

The difference between the amount of KE converted into heat over time.
A tree might well convert all of the KE it takes from the wind into heat and a windmill is designed to make electrical energy which ends up through use also into heat.
So the tree is more efficeint at produceing heat (converting KE into heat) though the amount of heat a 15M high tree produces is a lot less than a 60M windmill over the same period.

So you are abandoning your previous irrelevant claim about efficiency. That is good. We can dispense with that argument then.

You are making a new irrelevant claim about size. Fine. Windmills are bigger than trees. One windmill affects the wind more strongly than one tree.

So the more windmills built the more KE taken from the Earth's rotation and turned into heat which is lost in space.

That assumes that one windmill takes KE from the Earth's rotation and turns it into heat.

You have not provided any support for that assumption.

 

[A.T.]

So the more windmills built the more KE taken from the Earth's rotation

What makes you think that windmills slow down the Earth's rotation? Your own reference says that slowing down the winds (as windmills do) makes the Earth spin faster:

http://www.bbc.co.uk/blogs/legacy/23degrees/2011/03/can_an_earthquake_shift_the_ea.html

This happens because the northern hemisphere winds slow down in the summer and the momentum they lose - half the momentum of the atmosphere - is transferred to the Earth. This increase in momentum makes the Earth spin faster and our days become slightly shorter by 1-2 milliseconds.

 

[Buckleymanor]

What makes you think that windmills slow down the Earth's rotation? Your own reference says that slowing down the winds (as windmills do) makes the Earth spin faster:

http://www.bbc.co.uk/blogs/legacy/23degrees/2011/03/can_an_earthquake_shift_the_ea.html

Because all of the momentum from the wind is no longer transferred back to the Earth some of it is transferred to heat via the windmill and then lost to space.

 

[Dale]

Because all of the momentum from the wind is no longer transferred back to the Earth some of it is transferred to heat

This doesn't make sense. Heat is energy, not momentum. You are confusing the two again.

 

[A.T.]

Because all of the momentum from the wind is no longer transferred back to the Earth some of it is transferred to heat via the windmill and then lost to space.

As DaleSpam said, learn the difference between momentum and energy. Windmills transfer all of the momentum they extract from the atmosphere to the earth. No momentum at all is lost to space due to windmills. To lose angular momentum to space you need to apply an external torque from space.

 

[Buckleymanor]

As DaleSpam said, learn the difference between momentum and energy. Windmills transfer all of the momentum they extract from the atmosphere to the earth. No momentum at all is lost to space due to windmills. To lose angular momentum to space you need to apply an external torque from space.

So when the Earth spins faster due to a gain in momentum there is no increase in it's KE as the total system ie Earth atmosphere energy is conserved.
If that is the case then why all the bother about GW as this would indicate a gain in KE.

 

[jbriggs444]

So when the Earth spins faster due to a gain in momentum there is no increase in it's KE as the total system ie Earth atmosphere energy is conserved.
If that is the case then why all the bother about GW as this would indicate a gain in KE.

Without a net torque from outside, the Earth never spins faster due to a gain in angular momentum.

 

[A.T.]

the total system ie Earth atmosphere energy is conserved.

No, that is exactly backwards. Total angular momentum of Earth+atmosphere is conserved (ignoring the Moon's tidal torque). Total KE of Earth+atmosphere is being increased by the Sun powering the winds, and reduced by trees, windmills and other obstacles.

 

[Buckleymanor]

Without a net torque from outside, the Earth never spins faster due to a gain in angular momentum.

I don't understand, when you say without a net torque from outside, the Earth never spins faster due to a gain in angular momentum, do you mean space like A.T. mentioned.
If I pick up a rock from the top of a mountain and throw it to the floor won't the Earth's angular momentum be changed and the Earth will spin slightly faster?

 

[jbriggs444]

I don't understand, when you say without a net torque from outside, the Earth never spins faster due to a gain in angular momentum, do you mean space like A.T. mentioned.

Yes, by "outside", I mean outside the atmosphere, i.e. space.

If I pick up a rock from the top of a mountain and throw it to the floor won't the Earth's angular momentum be changed and the Earth will spin slightly faster?

The total angular momentum of the rock, the mountain and the rest of the Earth is unchanged by that action. Yes, this action will cause the Earth (including mountain and rock) to spin slightly faster. But it does not affect the total angular momentum.