[Bored chemist]

I made that point in my first post in this thread #38

The "point" you made back then was wrong.

[Petrochemicals]

Thanks petrochemicals, I made that point in my first post in this thread #38
BC every time you see trees bending in the wind. think about what age you were when you learnt about momentum.

Yep treat every post as if the poster has the starting sentence

i believe yet am not sure, i think this is how it works, ...........

[gem]

Hi all, thanks for the advice on the etiquette petrochemicals.
Halc I believe your final part of your post
( but momentum cannot so easily change without energy being involved.)
Is more in line with conservation laws previously stated. https://upload.wikimedia.org/wikipedia/commons/8/8f/Diagram_Systems.png
Also in post 110 you state LOD is not momentum, no it isn’t but it is the very accurate measure of angular velocity which is required to calculate the value of momentum, and rotational Kinect energy.
B/C I believe you’re familiar with the method of calculating changes in pressure/volume using gas laws due to an energy input, and we are all capable of observing the kinetic dynamics input to the earth’s surface.
Which has been measured to impact on LOD

[Bored chemist]

Also in post 110 you state LOD is not momentum, no it isn’t but it is the very accurate measure of angular velocity which is required to calculate the value of momentum, and rotational Kinect energy.

Related, but not the same thing.
There's also no dispute that the tides transfer angular momentum between the Earth and the Moon.

None of that is relevant.
If the  rotational kinetic energy of the Earth was being  dissipated by the weather at anything like the rate that the weather  picks up energy from the Sun, then the Earth would be slowing down a lot more.
Stonehenge wouldn't work.

But the energy coupled by the tides is much smaller so the rate of slowing is much smaller.
All the stuff about isolated systems and so on is just an illusion brought about by the fact that isolated systems are generally considered as thermodynamics and thermodynamics doesn't normally bother with angular momentum.



And the only reason you don't even try to answer the important question is that you know that you can't- because you know that you are fundamentally wrong and you are trolling.
If you aren't a troll, you should be able to answer this question:

Quote from: Bored chemist on Yesterday at 08:48:24

I'm still waiting for someone to explain how there's a change in angular momentum without a torque .
How do you get round this ?
Quote from: Bored chemist on 18/08/2020 18:12:27
The rate of change of angular  momentum is the torque divided by the moment of inertia.
If the torque is zero then the change in angular momentum is also zero.

[gem]

Hi all, we do appear to be repeating ourselves, but if you read back I am not arguing against the majority of what is stated, previously I mentioned there appear to be contradictory facts in regards in this aspect of the original question,  in the science world, which you disregarded and put any contradictions at Alan’s door, but I have continued to explore some of the contradictions, to some people’s frustration,  by way of the dynamics we can observe and put some values to within the conservation laws.
So revisiting the fact that angular  velocity and therefore momentum has stayed within such a tight range even though it skips about between 0.1 and 0.2 milli seconds daily, and has this 3 milli second range annually,  could have several explanations yours above being one of them.
However to move the discussion forward, do you accept that a proportion of these changes to LOD is due to frictional coupling of the atmosphere with the earth’s surface.

[Bored chemist]

but I have continued to explore some of the contradictions,

There are none.

However to move the discussion forward, do you accept that a proportion of these changes to LOD is due to frictional coupling of the atmosphere with the earth’s surface.

Yes and no.
On a day by day basis the earth's atmosphere moves about with respect to the Earth.
In simple terms if the air moves up (on average) then the Earth slows down and if the air moves down then the Earth speeds up (like the overused analogy of the skater pulling their arms in).
So, on a short term basis (and If I remember rightly Wiki says the relaxation time is a few days) then yes the air has an effect.

But in the long term, it can't.
In the long term the air and the ground are coupled together. They spin once a day.
Indeed to a good approximation both the angular momentum of the ground (and sea)  and the angular momentum of the atmosphere are pretty constant.
There are formulae for the moment of inertia of a rigid sphere and for a rigid spherical shell.
And yes, I am calling the atmosphere rigid- because it rotates as if it is. Essentially all of it goes round once a day. The weather adds "noise" to that rotation rate.

For every wind that's blowing the ground clockwise, there's another (on a long term average) blowing it counterclockwise.

But fundamentally, if you think the air is slowing the world down, you  still have to deal with this

Quote from: Bored chemist on Yesterday at 10:36:19
Quote from: Bored chemist on Yesterday at 08:48:24

I'm still waiting for someone to explain how there's a change in angular momentum without a torque .
How do you get round this ?
Quote from: Bored chemist on 18/08/2020 18:12:27
The rate of change of angular  momentum is the torque divided by the moment of inertia.
If the torque is zero then the change in angular momentum is also zero.

If you really think the Earth is slowing down because of the weather, just tell me where the torque comes from.
It can't be the air.
Or do you think the man on the truck is helping his mates?


momentum.png (229.19 kB . 293x364 - viewed 1727 times)

[gem]

Are his mates pulling or pushing 👁

Am assuming the yes part of (yes and no) is covered by your statement
(For every wind that's blowing the ground clockwise, there's another (on a long term average) blowing it counterclockwise.)
Then if you apply that logic to the original question you can alter the LOD by altering the coefficient of friction in one directions favour.

[Bored chemist]

Do you understand why the man on the truck isn't helping?

If you push the truck, the truck pushes back on you.
So, to achieve much, you need to brace yourself against something.
The man isn't helping because his feet are braced against the same thing that he is pushing.

Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?

Well  the only possible answer is "the ground" because that's the only thing it touches.
So, like the man on the truck, the air must push the ground forward just as much as it pushes back.

You don't even need the high school physics version. The middle school science version of Newton's laws of motion will do.
If the air pushes the  Earth then the Earth must push back on the air just as hard.
If the Earth pushes the air  then the air must push back on the Earth  just as hard.
Since they are the only things pushing eachother, the net effect is zero

[gem]

Which brings us back to energy input from outside the system as you state
(Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?)

What did push the air to get it moving

[Colin2B]

What did push the air to get it moving

Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.

[Bored chemist]

What did push the air to get it moving

The ground. That's my point.
The only thing the air can push is exactly the same ground that is the only thing it can brace itself against.
It's like the man on the truck.
He's not making it go faster.
The air is not making the earth fo faster (or slower).

Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.

That drives the big convection cells.
But those winds run North and South.

The rotation of the Earth pushed them out of line via Coriolis forces, but those affect the direction of the wind, They don't couple energy into it- not least because they act in the opposite direction when the wind returns. There isn't a vacuum at the equator. The air goes back to where it came from.
Like a ship sailing north or south the coriolis forces act sideways . That's at right angles to the direction of travel. So they don't do work and don't transfer energy.
That is the bit where Alan had mistaken the rudder for the engine.

[Bored chemist]

But fundamentally, if you think the air is slowing the world down, you  still have to deal with this
Quote from: Bored chemist on Yesterday at 11:27:05
Quote from: Bored chemist on Yesterday at 10:36:19
Quote from: Bored chemist on Yesterday at 08:48:24

I'm still waiting for someone to explain how there's a change in angular momentum without a torque .
How do you get round this ?
Quote from: Bored chemist on 18/08/2020 18:12:27
The rate of change of angular  momentum is the torque divided by the moment of inertia.
If the torque is zero then the change in angular momentum is also zero.

[Colin2B]

But those winds run North and South.

I was rather expecting him (maybe expecting too much) to work that out for himself.

[Bored chemist]

But those winds run North and South.

I was rather expecting him (maybe expecting too much) to work that out for himself.

He doesn't seem good at realising things, or he would work out that there's no torque, so there's no change in rotation rate.

[gem]

Colin you state
Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.
Which I believe is a reasonable description of an energy input to a system (the atmosphere ) that by Excitation of the air molecules changes the density and through these dynamics occurring you described changes it’s velocity, and therefore it’s momentum.

[Colin2B]

......through these dynamics occurring you described changes it’s velocity, and therefore it’s momentum.

What goes up .....
It changed velocity on the way up (+) and on the way down (-), mass of air displaced must equal mass doing displacing, nett effect ?
I haven’t been following this thread but I suspect this is what @Bored chemist is saying to you, you are dealing with a circulating system.
The surface winds in depressions (anticyclones) and cyclones also experience friction with the ground changing their velocity and causing them to back, but again circulating system, what goes one way returns the opposite way.

[Bored chemist]

Colin you state
Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.
Which I believe is a reasonable description of an energy input to a system (the atmosphere ) that by Excitation of the air molecules changes the density and through these dynamics occurring you described changes it’s velocity, and therefore it’s momentum.

Two things.
What goes up one day comes down another day.
And going up and down does not affect angular momentum.

So, once again...

But fundamentally, if you think the air is slowing the world down, you  still have to deal with this
Quote from: Bored chemist on Yesterday at 11:27:05
Quote from: Bored chemist on Yesterday at 10:36:19
Quote from: Bored chemist on Yesterday at 08:48:24

I'm still waiting for someone to explain how there's a change in angular momentum without a torque .
How do you get round this ?
Quote from: Bored chemist on 18/08/2020 18:12:27
The rate of change of angular  momentum is the torque divided by the moment of inertia.
If the torque is zero then the change in angular momentum is also zero.

[gem]

Hi all, so a couple of things
B/C you said.
Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?

Well  the only possible answer is "the ground" because that's the only thing it touches.
And then Colin said.
Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.
Which contradicts your action/reaction pairing, for the air striking any potential wind turbines as per the question.
In regards to the change in momentum of the atmosphere receiving electro magnetic radiation not being angular momentum, is precisely the point, therefore angular momentum is not conserved as stated by the laws of conservation.
Halc regarding whether the atmosphere should be behaving differently to how it is, if it’s angular momentum is disturbed by solar input I will address later.

[Bored chemist]

Which contradicts your action/reaction pairing, for the air striking any potential wind turbines as per the question.

No it does not.
Do you understand how up and down is different from side to side?
That's what Halc was referring to here

Momentum and velocity are vector quantities, but you're treating them like they are scalars.

Now, it seems I have been reasonably patient in rebutting your assertions and answering your questions.
Could you please return the compliment and address this which I have asked a dozen or more times

What provides the torque required to change the angular momentum (and thus the spin speed) of the Earth?

[Halc]

Now, think about it; when air pushes a windmill, what is it "braced" against? What pushed the air to get it moving?

That can't be right. Start with the whole system with zero relative motion. Sun heats air.  It pushes against other air to get moving.  The ground is stationary, so cannot get air moving east.  So for every eastbound gob of air, there is an equal and opposite westbound gob somewhere.  Each eventually hits a windmill or tree, and yes, that puts a bit of torque on the ground, but torque is a vector quantity, and all those east and westbound torques add up to pretty much nothing, especially over time. There is only imperceptible wiggles in the momentum of the atmosphere as those winds experience friction with the ground at different times.

Well  the only possible answer is "the ground" because that's the only thing it touches.

Air mostly touches other air, which is what gets it moving. The ground can't, because it is essentially stationary relative to the rotating frame. Coriolis force can't do it because it only works if the air is already moving. It just turns you (again, relative to the rotating frame), but it doesn't accelerate anything.

And then Colin said.

Not pushed, pulled - by gravity.
Cool air, heavier than warm air, falls to displace the air near ground which is warmed by sun.

Which contradicts your action/reaction pairing, for the air striking any potential wind turbines as per the question.

But there is an opposite reaction where the wind going the other way hits another turbine or tree or dune.
If there is only the one turbine pushing continuously in one direction, the whole atmosphere would eventually be moving at arbitrarily high speed in the opposite direction. This doesn't happen, but you seem to envision this strange singular point of force with no reaction force anywhere, in total violation of Newton's laws.

In regards to the change in momentum of the atmosphere receiving electro magnetic radiation not being angular momentum, is precisely the point, therefore angular momentum is not conserved as stated by the laws of conservation.

You say EM imparts no momentum (correct), therefore you conclude momentum is not conserved. That's right on par for you at least.

Halc regarding whether the atmosphere should be behaving differently to how it is, if it’s angular momentum is disturbed by solar input I will address later.

It is disturbed, just not in a way that involves wind turbines. Solar 'input' as you call it applies friction to the spin of the planet, which mostly transfers angular momentum from its rotation to its revolution. This mechanism, if left undisturbed, will eventually (long time, heap big zeros) transfer enough of that momentum that the moon will eventual collide with the planet. There's a fair chance that the planet will be destroyed before that happens, depending on how much mass the sun retains before it grows to 1au in radius.