[Bored chemist]

Actually, in context, I can.
...
At least Jaaanosik has recognised that he was wrong to say this, and gone away.
...

Keep dreaming , it is about the boundary conditions.
We cannot have right/wrong if were are not talking about the same observers and boundary conditions.

The boundary is perfectly clear and has been obvious all along from the thread title and the OP.
It's the planet Earth and its atmosphere.

Now, once again, since you said it was easy...

It is easy to show that adding energy to a rigid body can change the axis of rotation,

Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

[Jaaanosik]

Actually, in context, I can.
...
At least Jaaanosik has recognised that he was wrong to say this, and gone away.
...

Keep dreaming , it is about the boundary conditions.
We cannot have right/wrong if were are not talking about the same observers and boundary conditions.

The boundary is perfectly clear and has been obvious all along from the thread title and the OP.
It's the planet Earth and its atmosphere.

It was already pointed out to you that the rotation and rotational acceleration changes have to happen to conserve the total angular momentum.
The cause of the rotational inertia changes could be an energy of the Sun's heat.
The answer to the OP is yes, the windmills can affect the Earth's rotation.
The windmills are one piece of the complex friction layer between the atmosphere and the rigid ground.
Whatever tiny part the windmills play, it still will affect the Earth's rotation.

Now, once again, since you said it was easy...

It is easy to show that adding energy to a rigid body can change the axis of rotation,

Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

You do not stop with re-posting this and you fail to understand 'the boundaries' of what I was saying.
Please, stop being annoying.
Jano

[Bored chemist]

I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.

Now, once again, since you said it was easy...
Quote from: Bored chemist on 24/09/2020 19:01:18
Quote from: Jaaanosik on 24/09/2020 18:51:25
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

[Bored chemist]

Whatever tiny part the windmills play, it still will affect the Earth's rotation.

In the end, the windmill will fall into disrepair and be scrapped.
Do you accept that, at that time, the Earth will return to exactly the same rotation as it started with?
(All other things being equal)

[gem]

Hi all,

So BC when you stated:

Momentum is conserved during inelastic collisions.
That's how we can still do maths with them.

I already covered that momentum is conserved overall, In my last post.

However I also stated some of the angular momentum is transferred to momentum of other kinds, such as the momentum carried by sound  waves and water waves.

Therefore for angular momentum to be conserved overall requires a mechanism that converts this said momentum back to angular momentum of the solid earth or the angular momentum of the atmosphere, for your position to be credible.

[Bored chemist]

However I also stated some of the angular momentum is transferred to momentum of other kinds, such as the momentum carried by sound  waves and water waves.

The trouble there is that what you stated is wrong.
Angular momentum is conserved.
You don't convert linear to angular (or vice versa).
It's a bit like the fact that you can't convert energy to momentum.

Do you actually understand what "Conserved" means?

[Jaaanosik]

I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.

Now, once again, since you said it was easy...
Quote from: Bored chemist on 24/09/2020 19:01:18
Quote from: Jaaanosik on 24/09/2020 18:51:25
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

I was talking about the 3 axes of rotation and how the total angular momentum is being conserved even though the individual axis are changing, as per the video.
The angular velocity changes along the 3 axes.
An accelerometer on such body will not measure a constant acceleration/rotation during these changes.
What is your problem?

[Jaaanosik]

Whatever tiny part the windmills play, it still will affect the Earth's rotation.

In the end, the windmill will fall into disrepair and be scrapped.
Do you accept that, at that time, the Earth will return to exactly the same rotation as it started with?
(All other things being equal)

No, because, it depends...

[Bored chemist]

Whatever tiny part the windmills play, it still will affect the Earth's rotation.

In the end, the windmill will fall into disrepair and be scrapped.
Do you accept that, at that time, the Earth will return to exactly the same rotation as it started with?
(All other things being equal)

No, because, it depends...

Well, OK, we are back to the thing you said was easy, but failed to do.

I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.

Now, once again, since you said it was easy...
Quote from: Bored chemist on 24/09/2020 19:01:18
Quote from: Jaaanosik on 24/09/2020 18:51:25
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

What is your problem?

The fact that you didn't answer the question.

You seem to think that resolving the angular momentum into 3 components matters.
It doesn't.

The cat walked past; I stroked it.
From my point of view, it was stroked left to right.
From the cat's perspective it was front to back.
A passing boy scout consulted his compass and concluded that it was North westerly.
A flea on the cat thought it was bottom to top

But, no matter what coordinates you pick, the actual event was the same.
And if you got any of the observers to do the maths they would all agree that from the point of view of a bee that was circling the cat's body, the stroke was a spiral.


The angular momentum of the Earth is also a thing that's fixed.
You can pick any set of coordinates and you can, if you wish, resolve it onto a set of cartesian ones.

But it's still conserved.
Obviously, if you change the coordinate system then the numbers you assign to the component vectors will change, but the momentum is still conserved.

An accelerometer on such body will not measure a constant acceleration/rotation during these changes.

How fortunate, then, that nobody asked what an accelerometer would say.

[gem]

Hi all
Ok BC you state:

“The trouble there is that what you stated is wrong.
Angular momentum is conserved.“

So it is stated and you have stated also angular momentum is transferred between the earth’s surface/atmosphere due to frictional coupling.

Are you now arguing this is done silently and therefore no momentum is transferred outward in all directions from the points of friction.?

[Bored chemist]

What I have said (well, it's not me saying it; it's physics) is that linear momentum is conserved, angular momentum is conserved and energy is conserved. They are all conserved quantities
You seem to have become muddled.
It is possible to convert energy from one form to another- for example you can convert light energy into kinetic energy

But it is not possible to interconvert any of the three conserved quantities,
So, for example, you can not convert linear momentum into angular momentum.

Are you now arguing this is done silently and therefore no momentum is transferred outward in all directions from the points of friction.?

Obviously, I didn't say that.
You just made it up and it's a bit silly.

[Jaaanosik]

Whatever tiny part the windmills play, it still will affect the Earth's rotation.

In the end, the windmill will fall into disrepair and be scrapped.
Do you accept that, at that time, the Earth will return to exactly the same rotation as it started with?
(All other things being equal)

No, because, it depends...

Well, OK, we are back to the thing you said was easy, but failed to do.

I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.

Now, once again, since you said it was easy...
Quote from: Bored chemist on 24/09/2020 19:01:18
Quote from: Jaaanosik on 24/09/2020 18:51:25
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

What is your problem?

The fact that you didn't answer the question.

You seem to think that resolving the angular momentum into 3 components matters.
It doesn't.

The cat walked past; I stroked it.
From my point of view, it was stroked left to right.
From the cat's perspective it was front to back.
A passing boy scout consulted his compass and concluded that it was North westerly.
A flea on the cat thought it was bottom to top

But, no matter what coordinates you pick, the actual event was the same.
And if you got any of the observers to do the maths they would all agree that from the point of view of a bee that was circling the cat's body, the stroke was a spiral.


The angular momentum of the Earth is also a thing that's fixed.
You can pick any set of coordinates and you can, if you wish, resolve it onto a set of cartesian ones.

But it's still conserved.
Obviously, if you change the coordinate system then the numbers you assign to the component vectors will change, but the momentum is still conserved.

An accelerometer on such body will not measure a constant acceleration/rotation during these changes.

How fortunate, then, that nobody asked what an accelerometer would say.

The OP question is about rotation and acceleration.
Why are you talking about the angular momentum?


Imagine, you are floating inside of the International Space Station.
Not moving, no rotation, nothing.
Can you flip 180 degrees without touching anything, just with your motion?

[Halc]

Just pointing out some continued mistakes being continuously asserted by one or the other of you, none of which has been backed by anything other than empty assertions.

Imagine, you are floating inside of the International Space Station.
Not moving, no rotation, nothing.
Can you flip 180 degrees without touching anything, just with your motion?

Cats are legendary for being able to do this in well under a second, but they don't change their angular momentum in doing so. Neither do the objects in the video change their axis of rotation (except one, and that one depicts a violation of physics). The angular momentum vector in each example wavers neither in magnitude nor direction.

It is easy to show that adding energy to a rigid body can change the axis of rotation, changing the direction of the rotation.

As B-C has repeatedly pointed out, this statement is just plain wrong, and yes, we've both noticed that despite the claimed ease of showing this, you've not shown it. That makes you full of hot air, but said hot air doesn't change the momentum of your argument.

However I also stated some of the angular momentum is transferred to momentum of other kinds

So if there is friction, for both linear and angular momentum means the collision is not perfectly elastic, and therefore a percentage of momentum is transferred to the thermal motion of particles, whether within the earth's surface or the gas particles of the atmosphere.

So if calculated at that instance of transfer, it would be calculated momentum is conserved, overall but the linear/angular
momentum will have altered.

All of these assertions violate the laws of momentum conservation. A collision between two masses has the exact same momentum (both linear and angular) as before the collision, whether the collision is elastic or not. The latter case ends up with warmer masses perhaps, but no difference in the momentum of the system.

[Jaaanosik]

Just pointing out some continued mistakes being continuously asserted by one or the other of you, none of which has been backed by anything other than empty assertions.

Imagine, you are floating inside of the International Space Station.
Not moving, no rotation, nothing.
Can you flip 180 degrees without touching anything, just with your motion?

Cats are legendary for being able to do this in well under a second, but they don't change their angular momentum in doing so. Neither do the objects in the video change their axis of rotation (except one, and that one depicts a violation of physics). The angular momentum vector in each example wavers neither in magnitude nor direction.

It is easy to show that adding energy to a rigid body can change the axis of rotation, changing the direction of the rotation.

As B-C has repeatedly pointed out, this statement is just plain wrong, and yes, we've both noticed that despite the claimed ease of showing this, you've not shown it. That makes you full of hot air, but said hot air doesn't change the momentum of your argument.

However I also stated some of the angular momentum is transferred to momentum of other kinds

So if there is friction, for both linear and angular momentum means the collision is not perfectly elastic, and therefore a percentage of momentum is transferred to the thermal motion of particles, whether within the earth's surface or the gas particles of the atmosphere.

So if calculated at that instance of transfer, it would be calculated momentum is conserved, overall but the linear/angular
momentum will have altered.

All of these assertions violate the laws of momentum conservation. A collision between two masses has the exact same momentum (both linear and angular) as before the collision, whether the collision is elastic or not. The latter case ends up with warmer masses perhaps, but no difference in the momentum of the system.

Did I say that the total angular momentum is not conserved?
Yet, consider the following, if an astronaut can rotate 180 degrees then what stops him from rotating continuously without stopping?
In the beginning, no rotation, no motion and then continuous rotation.
The rotation changed but the total angular momentum is conserved.

[Halc]

Did I say that the total angular momentum is not conserved?

It is easy to show that adding energy to a rigid body can change the axis of rotation, changing the direction of the rotation.

If the direction of rotation is changed, the angular momentum is not conserved now, is it? So yes, you've been asserting just that.

It also is not confined to rigid bodies.  A system of masses connected with pool noodles or not connected at all will still maintain both linear and angular momentum, absent external forces.  Energy input (in a form other than external force/torque over distance) makes no difference.  I can also apply an external force or torque (and change the respective momentum) without application of external energy, so the momentum is simply not a function of energy input.

[Bored chemist]

Why are you talking about the angular momentum?

Well, for a more or less rigid body like the Earth they are so closely related that it doesn't matter.

Are you considering that idea that someone might move enormous quantities of rock from the equator to the poles?
That's what it would need before that interesting but irrelevant video of the flipping wingnut applied to our planet.
It's also important to recognise that during its flight the angular momentum of the wingnut is conserved.

The reason for choosing angular momentum is ironically illustrated by Gem who pointed out that energy is the currency of physics  or some such.
Well, it's only one of the currencies in use.
You choose the conserved property that best fits the situation and, in this case it's angular momentum.

A much better question is why are you ignoring it?
In particular, why are you ignoring the fact that angular momentum is conserved.
If the Earth doesn't change its shape or the distribution of its mass then the moment of inertia , and thus the rotation rate, will be constant.
Windmills don't do that (or, rather they do, but less so than a block of flats or a grain silo; it's not "being a windmill" that makes the difference).

Did I say that the total angular momentum is not conserved?

Yes.
Repeatedly.
You just don't seem to understand that you did so.
Any change in the rotation of the Earth is a change in angular momentum.

Your failure to understand this simple bit of physics is also shown by you asking this

Why are you talking about the angular momentum?

Can you flip 180 degrees without touching anything, just with your motion?

Yes.
Position is not a conserved quantity

Yet, consider the following, if an astronaut can rotate 180 degrees then what stops him from rotating continuously without stopping?

The conservation of angular momentum.
He starts with zero, so he must end up with zero.
During the maneuver, he imparts equal and opposite angular momenta to his leg and to the rest of his body. but the sum remains zero.
He can do this because he is flexible and has muscles which apply forces.
Cats are also noted for the ability to do it, and for their flexibility.
However the Earth is , for all practical purposes, rigid.


(It's interesting to note that, in principle, it's possible to make the change of direction in which you face without expending energy).

The rotation changed .

Not really. It remains zero at all times.
The clever bit is that his leg(s) rotates in the opposite direction to the rest of him.
https://space.stackexchange.com/questions/2954/how-do-astronauts-turn-in-space

So , once again...

Quote from: Bored chemist on Yesterday at 17:25:59
I will stop posting this when you either show that it was easy as you claim, or accept that it's impossible because the laws of physics prevent it.

Quote from: Bored chemist on 05/10/2020 18:31:40
Now, once again, since you said it was easy...
Quote from: Bored chemist on 24/09/2020 19:01:18
Quote from: Jaaanosik on 24/09/2020 18:51:25
It is easy to show that adding energy to a rigid body can change the axis of rotation,
Then show it.
But no cheating.
You have to do it without applying a torque.
Only add energy.

You keep on saying you can perform this miracle and that it's easy.
Why don't you do it?

[gem]

Hi all
So Halc you state:
A collision between two masses has the exact same momentum (both linear and angular) as before the collision, whether the collision is elastic or not. The latter case ends up with warmer masses perhaps, but no difference in the momentum of the system.

So to be clear is the momentum of the said matter effected by the collisions that is the vibrations and movement within a particles freedom of movement, included in your version of the sum of conservation ?
Also is the momentum carried Out in all directions by the sound waves included in your calculations?

[Bored chemist]

Also is the momentum carried Out in all directions by the sound waves included in your calculations?

By symmetry, that sums to zero anyway.

Do you actually understand what "Conserved" means?

is the momentum of the said matter effected by the collisions that is the vibrations and movement within a particles freedom of movement, included in your version of the sum of conservation ?
Also is the momentum carried Out in all directions by the sound waves included in your calculations?

So, that's a "no" then. You do not know what "conserved" means or you would not have asked that.

[Halc]

So to be clear is the momentum of the said matter effected by the collisions that is the vibrations and movement within a particles freedom of movement, included in your version of the sum of conservation ?

A cold 1kg mass moving at 2 m/sec north has the exact same momentum as a hot 1kg mass moving at 2 m/sec north, so the difference is only thermal energy.  Yes, the particles in the latter are moving at a higher average speed, but not at a higher average velocity, and momentum is a function of velocity, not speed.

One is a scalar quantity, and one a vector quantity, and you cannot substitute one for the other, as B-C has already pointed out, but if you don't listen to him, why should you listen to me?

Also is the momentum carried Out in all directions by the sound waves included in your calculations?

Sound waves carry energy but not momentum. That means a perfectly elastic collision between objects cannot make any sound.  The inelastic collision can, but if the system is moving through a medium which carries sound (air), they're probably losing momentum due to friction with the air. That would constitute an external force upon the system.

This is not the case with Earth as a system.  It makes no sound as it travels through space.

[Jaaanosik]

Did I say that the total angular momentum is not conserved?

It is easy to show that adding energy to a rigid body can change the axis of rotation, changing the direction of the rotation.

If the direction of rotation is changed, the angular momentum is not conserved now, is it? So yes, you've been asserting just that.

It also is not confined to rigid bodies.  A system of masses connected with pool noodles or not connected at all will still maintain both linear and angular momentum, absent external forces.  Energy input (in a form other than external force/torque over distance) makes no difference.  I can also apply an external force or torque (and change the respective momentum) without application of external energy, so the momentum is simply not a function of energy input.

The bold part, I am talking about three axes of rotation.
These axes are defined with relation to the body.
The angular momentum changes between them but there is no total sum gain.
Like the cats rotation, applying energy within the system can be a cause of such rotation.

This is a quote from that video description:

This, together with the centrifugal effects, means that the components of momentum DO change.

The analysis of 'one of the best mathematicians' of our time, as per the video, switched to a non-inertial observer.