[alancalverd]

Are you saying that we can extract energy from the rotation of the Earth without slowing that rotation down?

No.

Or are you saying you can slow down the Earth's rotation without an external torque?

Yes.

[Bored chemist]

Oh but I am. Every time I plot a course, descend through the predicted wind shear, and find myself lined up with the runway I think "This can't be true, because BC says I don't know what I'm doing". Nothing to do with physics - aviation is the triumph of wishful thinking.

Straw man.
Plenty of people drive cars with little or no understanding of what makes them work.
It seems you ride the wind while thinking it's provided by fairies.
That's fine- as long as the fairies produce the same wind as actual physics does.
(Sorry, my mistake; not fairies, but a non existent torque on the Earth- the argument is the same.)
Incidentally, I presume you think that they typically launch  balloons at dawn because that's when the world stops spinning and there is consequently little wind. Similarly you presumably imagine that the winter storm season coincides with when the Earth speeds up and we all need to reset our clocks.

Are you saying that we can extract energy from the rotation of the Earth without slowing that rotation down?

No.

Or are you saying you can slow down the Earth's rotation without an external torque?

Yes.

OK, so it's the conservation of angular momentum that you don't accept.

Well, please yourself, but this is a science site so you might get laughed at.

[alancalverd]

Angular momentum is conserved in a closed system.
Consider a spinning electric motor. Disconnect the supply current and connect the motor terminals via a resistor. The kinetic energy of the armature Iω² is dissipated as heat (the simple electromagnetic brake) and ω→0.
Does the angular momentum Iω remain constant?   

[Bored chemist]

Angular momentum is conserved in a closed system.

Like the Earth.

Does the angular momentum Iω remain constant?   

Yes.
Because it's a conserved quantity.

If the motor is floating in space with you watching it from a distance lets simplify things by saying that the stator starts off stationery from your PoV and the rotor is spinning.
The fact that it is a motor dissipating heat in a resistor is irrelevant.
Because the bearings are imperfect, the rotor will apply a torque to the stator and will cause it to accelerate.
The stator will speed up and the rotor will slow down until they are both rotating at the same rate.
If you use the motor to generate current and feed that into a resistor then the magnetic field does the same as a bad bearing. It transfers energy quicker.
The outcome is the same, the rotor and stator will come to rest WRT each other, but they will be spinning from your point of view.

And the angular momentum of the system as a whole- the rotor and stator will remain constant.
If you want to change it then you need to apply an external torque.

So, for the (about) twelfth time, what do you think applies an external torque to the Earth in order to change its angular momentum?

[gem]

I understand your logic B/C given the plus or minus 1.5 milli seconds is nailed on every year  related to earth’s orbit and yes the increase/decrease in energy is
1316.75/1407.88 watts m^2 of cross sectional area so a delta of 6.5%. Of solar energy received.

However the length of day is taken from Earth’s surface and the atmosphere is uncoupled from earth, apart from its frictional coupling at the earth’s surface.
Therefore not a satisfactory explanation.
There are similar contradictions in the current explanations as to this effect.

[Bored chemist]

However the length of day is taken from Earth’s surface and the atmosphere is uncoupled from earth, apart from its frictional coupling at the earth’s surface.

That's all it takes to couple them . It might take a short while to catch up, but the air moves pretty much with the Earth.
If it didn't there would be the 1000 MPH wind at  the equator.

There are similar contradictions in the current explanations as to this effect.

There's only 1 contradiction in Alan's explanation.
He says the Earth is slowing down and thereby coupling energy onto the wind and weather, but without an external torque, that's impossible.

just like the ice skater moving his/her arms further out from the axis of rotation.

When the (idealised) skater stops waving their arms about, they are spinning at exactly the same rate as when  they started.

[alancalverd]

That's all it takes to couple them . It might take a short while to catch up, but the air moves pretty much with the Earth.
If it didn't there would be the 1000 MPH wind at  the equator.

You are beginning to get the idea. Because the equator is moving at 1000 mph, and the poles at 0 mph, an equatorial air mass moving north or south will move over the surface (i.e. generate wind) at the initial rate of about 11 mph per degree  thanks to the conservation of its momentum.

[Bored chemist]

You are beginning to get the idea. Because the equator is moving at 1000 mph, and the poles at 0 mph, an equatorial air mass moving north or south will move over the surface (i.e. generate wind) at the initial rate of about 11 mph per degree  thanks to the conservation of its momentum.

And you too are beginning to get it.
The important thing to realise is that the air doesn't all stay at the pole.
The air, on the way back, it accelerates sideways again, exactly compensating for the change in angular momentum on the pole-ward journey- which is HOW momentum is conserved.
And, you also forgot the important thing.
Why would the air be moving Northwards?
Clue- it's a convection cell driven by a hot thing nearby.
So, while the Earth's spin affects the direction of the wind, the actual power behind is is solar.
As I said, you have mistaken the rudder for the engine.

And so, for the 13th time, what causes the external torque needed to change the rotation rate of the Earth?

David, as I discovered along time ago that in the long term the only way to affect the earths ;

position in space
Orbital speed
Moon
Tides
Etc


Is you

have to exeed the maximum surface escape velocity of the earth moon system

In a very real sense.
But, in  a rather more real sense, the Moon is one of the few things that is having a measurable effect on the spin of the Earth and, since it's still here, it can't exceed escape velocity.

[alancalverd]

The air, on the way back, it accelerates sideways again, exactly compensating for the change in angular momentum on the pole-ward journey- which is HOW momentum is conserved.

But at some point in its journey, the air mass has transferred some momentum to the windmill, one hopes.

Though it has been admitted that some small windmills actually consume electricity when there is no wind, because the public object to stationary windmills!

[Bored chemist]

But at some point in its journey, the air mass has transferred some momentum to the windmill, one hopes.

It doesn't matter if the drag on the air is caused by friction at the Earth's surface or a windmill.
Anyay, none of that can transfer any angular  momentum off the planet, so it can't affect the rate of rotation of the Earth.

So, for the 14th time what causes the external torque needed to change the rotation rate of the Earth?

[gem]

Hi all, David’s analogy re the rotation of a satellite clearly describes the fundamentals of conservation of momentum, however there is the counter argument of rather than losing gas to gain an external torque force, you could have a external energy source to gain propulsion, think solar sails work on this principle.

[Bored chemist]

clearly describes the fundamentals of conservation of momentum,

Not entirely clear.

If you have a satellite that's rotating slightly, you can presumably stop that using the gyroscopes, but only at the cost of having to run them continually. To stop the rotation so that you don't have to run motors all the time

If the bearings are good (and they are) you don't need to run  motor to keep the gyro spinning.

[gem]

I don’t know much about the efficiency of the bearings, but the analogy with the caveat I posted, demonstrates the counter argument of energy gain having to be considered, in a non closed system, can also ultimately effect, positively or negatively, the rotational Kinect energy
Rather than just the loss to the system.

[Bored chemist]

You can't change the rotation rate unless you change the moment of inertia or you add (or subtract) angular momentum.
And we are waiting for Alan to explain where that angular momentum goes to, or comes from.
You can move some to or from the atmosphere, but not for long because viscous drag shifts it back to the ground.
And that's the point.
Like the skater who stops waving their arms about, in the long run, there's no change in spin rate.
And if there's no change in spin rate (and no change in I) there can't be a change in rotational energy.
And if there's no change in rotational energy then no energy can be coupled into the weather.

We are now all waiting for Alan to get to grips with that simple physics, and accept that he was mistaken.

[gem]

I believe if you have inelastic collisions between the atmosphere and earth’s surface, rotational energy can be reduced/increased And energy transferred in to other forms.
As per the laws of conservation of energy..
The biannual +- 1.5 milli second variation we were discussing earlier is causing active research Because once atomic clocks came into service to monitor LOD, it was proven weather patterns especially near mountain ranges gave a measurable effect to length of day
 (variation of velocity in the x direction)
However currently there is a known shortfall in the calculations of angular momentum in the atmosphere to correlate with this phenomenon.
Which brings us back to the crux of the original question of should we have to give any consideration to the aspect to the design positions and increasing numbers of wind turbines.

[Bored chemist]

I believe if you have inelastic collisions between the atmosphere and earth’s surface, rotational energy can be reduced/increased

Yes, once, until the atmosphere is rotating at the same rate as the Earth.
It's like the case of the motor and stator.
Once they are rotating at the same rate (and they are) there's no longer a net transfer of momentum or  energy.

[gem]

Given the continuing and constant dynamics of the atmosphere due to earth’s weather patterns moving the molecules at varying velocities within the atmosphere due to variations in temperature and pressure, due to suns energy input, therefore variations in the atmospheres velocity relative to the earth’s surface, that we can observe pretty much on a daily basis.
Which is known to still effect the LOD (Angular momentum) and given that the atmospheres interaction with the earth’s surface is not elastic, how is angular moment kept separate from these transfers of energy to other forms  .

[Bored chemist]

It's high school physics to know that the requirement for momentum and energy to be conserved implies that some collisions must be inelastic.
The same is true of connecting a charged capacitor and an uncharged one- conservation of charge means that some energy has to be dissipated.

But it still remains the case that Alan needs to explain an external torque if he wants the world to slow down.

So far, he hasn't tried and I suspect that's because, for all his bluster, he knows he was wrong.

[gem]

Just in case any high school pupils or teachers read this, the requirement for momentum and kinetic energy to be conserved is, all collisions have be to be elastic, however momentum is conserved in inelastic collisions, in a isolated/closed system.

Therefore the criteria for  conservation Of momentum being Relevant and an outside torque force required to alter earths overall angular momentum are,

a physical system so far removed from other systems that it does not interact with them.
And/or
a thermodynamic system enclosed by rigid immovable walls through which neither mass nor energy can pass.

Therefore earth’s rotational energy and momentum cannot be conserved.

[Bored chemist]

Therefore earth’s rotational energy and momentum cannot be conserved.

That's correct, but I got tired of repeating the phrase "apart from the tidal drag effects of the Moon etc" or words to that effect.
And it's also true in that there can be an exchange of momentum between the atmosphere (or bits of it) and the Earth, but that's going to average out to zero. What is gained by 1 is lost by the other. The sum is constant. Angular momentum of "the planet + its atmosphere" is conserved.
There's also the change in angular velocity which takes place when I climb the stairs.
But that's reversed when I come back down again.

I'm happy to discuss things like the Earth's emission of gravity waves, but I think it's a stretch to say they drive the weather.
The Earth's motion round the Sun must have a tidal effect on both bodies and thus dissipate kinetic energy, but again, that's not what couples energy from the rotation of the Earth into our weather.

Therefore earth’s rotational energy and momentum cannot be conserved.

If you are saying they are not conserved then there has to be an interaction of the Earth with something else.
That interaction will be a torque (or it won't affect the angular momentum).
So, like Alan, you are left trying to explain what the source of that external torque might be