[alancalverd (OP)]

[Mod edit: Topic split from "Can windmills affect Earth's rotation?"]
https://www.thenakedscientists.com/forum/index.php?topic=80136.0


Any windmill extracts kinetic energy which we eventually turn into heat.

Ignoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

Now that really will induce some climate change!   

[Bored chemist]

gnoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

And there was me thinking that the Sun powered the wind.

[Bored chemist]

so it must eventually stop spinning.

Just as soon as it gets hold of something to which it can impart angular momentum.
Tricky for something  in a near vacuum.
Might need to wait until the Sun goes red giant.

[chiralSPO]

so it must eventually stop spinning.

Just as soon as it gets hold of something to which it can impart angular momentum.
Tricky for something  in a near vacuum.
Might need to wait until the Sun goes red giant.

Well, the moon is taking some... but tidally locked to the moon is also not "stopped"

gnoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

And there was me thinking that the Sun powered the wind.

I'm with Bored on this one. Thermal effects (wind) are only secondary to the rotation of the earth if your frame of reference is not tethered to the earth. If you wanna argue that the atmosphere is moving with the earth at several thousand kph, that windmill had better be inbound from outer space!

[alancalverd (OP)]

gnoring second-order effects such as thermal winds, the source of kinetic energy is the rotational energy of the planet, so it must eventually stop spinning.

And there was me thinking that the Sun powered the wind.

Not a lot. Solar heating is responsible for the slow, gross convective movement of large air masses towards and away from the poles, but the formation of cyclones is powered by the coriolis displacement of those masses. The wind in the Southern Ocean is almost entirely due to the earth's spin as there is almost no land to produce differential heating, which is why albatrosses live the way they do, reliant on a constant westerly to keep them airborne for years at a time.   

[Petrochemicals]

If you take the energy out of the wind in an eastward direction the waves will not be generated in that direction and trees will not blow thus meaning the earth is slowed more by the windmill but less by the environment.

[Bored chemist]

OK
The spinning Earth has enormous rotational KE.
But it can't transfer that energy without slowing itself down.

And it can't slow itself down without an external torque.
Now, the geothermal energy, and the tides might make small contributions but they really don''t do "weather".

So, the fundamental question for you to answer Alan, is this.
Are you abandoning the conservation of energy, or abandoning the conservation of angular momentum?

[Bored chemist]

If you take the energy out of the wind in an eastward direction the waves will not be generated in that direction and trees will not blow thus meaning the earth is slowed more by the windmill but less by the environment.

It's all very clever, and very grown up, to proclaim that you are ignoring me, but you are also ignoring physics.
Windmills can't slow the Earth.
You need to consider the reaction forces at the foot of the windmill and the conservation laws.

[alancalverd (OP)]

OK
The spinning Earth has enormous rotational KE.
But it can't transfer that energy without slowing itself down.

And it can't slow itself down without an external torque.
Now, the geothermal energy, and the tides might make small contributions but they really don''t do "weather".

So, the fundamental question for you to answer Alan, is this.
Are you abandoning the conservation of energy, or abandoning the conservation of angular momentum?

Apologies - I hit "modify" instead of "quote", but I think it's clear what you were referring to.

For the sake of public safety, please publish the registration number of your car, as you say the brakes don't work.

And how sad that James Joule wasted his honeymoon.

[Bored chemist]

I don't drive- it's a public service I offer the rest of the world for free.

But, many years ago I did an O level physics module on the physics of the motor car.
And they did explain things like brakes.
One thing which they didn't need to explain was that, if you hit a bump, and your car leaves the ground, the brakes and steering have no effect (neglecting air resistance) until you hit the ground again.

The Earth is perpetually in flight (well, in orbit...) and in the vacuum of space, it's perfectly sensible to ignore air resistance.

So apart from the Moon's tidal drag, what torque acts on it to alter its angular momentum?

Because, without such a torque, the rate of spin will remain the same.
And, if the rotation rate remains the same, then its rotational kinetic energy remains the same.
And if its energy is the same, it can't be giving up energy to drive the weather.

And- this is England- we have plenty of weather, so something must be driving it.
And - even in England- the Sun provides huge amounts of power, which has to go somewhere somehow.


The world's weather is a giant heat engine driven by the Sun.


So, rather than making silly comments about my (non existent) driving, perhaps you can tell us what provides the torque that slows the Earth?
(Hint; it's not atmospheric drag; there isn't a 1000 MPH wind running round the equator)

[alancalverd (OP)]

The prevailing geostrophic wind is the result of coriolis force making the air move relative to the surface of the earth. The coriolis force is a consequence of the spin of the earth. If we extract kinetic energy from the geostrophic wind and dissipate it as heat, whence came that energy? The only source is the spin of the earth.

The function of a vehicle brake is to convert the kinetic energy of the vehicle to heat. Same thing.  Conservation of momentum means that applying the brakes whilst airborne will stop the wheels spinning but won't dissipate much energy, but if they are in contact with the ground (a very large mass) you can generally bring the vehicle to a standstill.

[Bored chemist]

but if they are in contact with the ground (a very large mass) you can generally bring the vehicle to a standstill.

So, what's the corresponding "very large mass" that the Earth is in contact with and which can slow it down?
Essentially you are still ignoring the conservation laws.

Without an externally acting torque, the world keeps spinning.

So, rather than making silly comments about my (non existent) driving, perhaps you can tell us what provides the torque that slows the Earth?
(Hint; it's not atmospheric drag; there isn't a 1000 MPH wind running round the equator)

[alancalverd (OP)]

(Hint; it's not atmospheric drag; there isn't a 1000 MPH wind running round the equator)

Now who's being silly?  "Wind" is air moving over the ground. The surface air at the equator is moving 1000 mph faster than that at the poles, but neither mass is moving very fast over the ground. Now if we take a sample of equatorial air and adiabatically move it 1 degree north, it will be travelling over the ground at about 11 mph. The same volume of air moving 1 degree southward from a northern latitude will be travelling on the opposite direction. That is the origin of geostrophic wind: the north-south movement of air masses is due to temperature differential (cold dense air sinks below warmer air, so the surface drift is from pole to equator), and the east-west movement is due to coriolis force.   

[Bored chemist]

Now who's being silly? 

Well, since you are sticking with your idea that the wind can slow down the rotation of the Earth in the long run... you.

Now, for the 3rd or 4th time

perhaps you can tell us what provides the torque that slows the Earth?

Hint: it can't be the atmosphere because that's rotating along with,and is part of, the Earth. If it wasn't then there would be a 1000 mph wind round the equator.

[Bored chemist]

Now if we take a sample of equatorial air and adiabatically move it

What moved it (Hint, it's convection currents driven by the Sun)?
A ship sailing due north has to overcome coriolis forces, but that doesn't mean they can switch off the engine.
The engine has to work harder.

[alancalverd (OP)]

Well, since you are sticking with your idea that the wind can slow down the rotation of the Earth in the long run... you.

Please don't ascribe irrelevant ideas to me.

[Bored chemist]

Well, since you are sticking with your idea that the wind can slow down the rotation of the Earth in the long run... you.

Please don't ascribe irrelevant ideas to me.

You are saying that the wind takes energy from the rotation of the Earth.

If we extract kinetic energy from the geostrophic wind and dissipate it as heat, whence came that energy? The only source is the spin of the earth.

Are you saying it does that without slowing the Earth down?
That's plainly a breach of the conservation of energy.
So Either you are being absurd and ignoring the laws of physics (spoiler alert- you are anyway) or you are saying that "the wind can slow down the rotation of the Earth in the long run" but not being bright enough to recognise that you are saying it.
So I'm not ascribing an irrelevant idea to you.
I'm just pointing out that your idea is absurd.

[David Cooper]

I'm not sure who's right here, but if you think about the way the equator of the sun rotates at a higher rate than the poles and how the core of the Earth rotates at a higher rate than the crust, it appears that are things that can happen with rotating liquid gas and plasma bodies which are able to cause drag and generate heat, but does that change the angular momentum?

[Bored chemist]

, but does that change the angular momentum?

No.
Because only an external torque can do that.
There are small effects due to tide and even smaller ones due to radiation pressure
Things like earthquakes alter the  distribution of the mass and thus the moment of inertia, and that alters the rate of rotation very slightly.

This isn't hard.
Angular momentum is a conserved quantity

[Bored chemist]

Now, for the 3rd or 4th time
Quote from: Bored chemist on 02/08/2020 12:13:33
perhaps you can tell us what provides the torque that slows the Earth?
Hint: it can't be the atmosphere because that's rotating along with,and is part of, the Earth. If it wasn't then there would be a 1000 mph wind round the equator.

I checked, it's the fifth time of asking.