[Geezer]

Newtons laws show that there would be no net effect.

BC, think about that the next time you are in an aeroplane, because, if you are right, it ain't going anywhere.

A lot of people might have correctly assumed that I meant no effect on the Earth's rotation.

Obviously there would be effects. For example, if you were behind the cows you would probably notice. If you were smoking at the time you might notice something else too.
However neither the flatulent cows, not my air travel make much odds to the Earth's rotation.

If the cows were all pointing their bums in the same direction, the net effect would be nonzero. Admittedly it would be very difficult to detect the effect, but Newton's laws would still apply.

[Airthumbs (OP)]

I think science is fantastic when you can get the most intellectual people on here to state that "yes, them there cow farts all lined up would be changing the earths rotation"  According to Newton that is.

I say that with the greatest of respect because most of the time the same people post stuff about quantum physics and particle accelerators that I find tough to grasp..   []

[Bored chemist]

Newtons laws show that there would be no net effect.

BC, think about that the next time you are in an aeroplane, because, if you are right, it ain't going anywhere.

A lot of people might have correctly assumed that I meant no effect on the Earth's rotation.

Obviously there would be effects. For example, if you were behind the cows you would probably notice. If you were smoking at the time you might notice something else too.
However neither the flatulent cows, not my air travel make much odds to the Earth's rotation.

If the cows were all pointing their bums in the same direction, the net effect would be nonzero. Admittedly it would be very difficult to detect the effect, but Newton's laws would still apply.

Still wrong.
http://en.wikipedia.org/wiki/Angular_momentum

[imatfaal]

two rockets diametrically oppposed and with opposite direction of thrust constitute an external torque; otherwise a catherine wheel wouldn't spin and a spacecraft wouldnt be able to change its inclination, heading, or yaw

[Airthumbs (OP)]

So would two diametrically cows operate in the same way, given that the thrust is generated by, well you know what, lol

[Geezer]

BC - Angular momentum only applies to a rigid body.

It's simply a case of F=ma. The accelerated mass of methane results in a force that applies a torque, communicated through the cow's hooves, to the Earth.

If angular momentum was conserved, jet engines (or rockets for that matter) would not work.

[JP]

Newtons laws show that there would be no net effect.

BC, think about that the next time you are in an aeroplane, because, if you are right, it ain't going anywhere.

A lot of people might have correctly assumed that I meant no effect on the Earth's rotation.

Obviously there would be effects. For example, if you were behind the cows you would probably notice. If you were smoking at the time you might notice something else too.
However neither the flatulent cows, not my air travel make much odds to the Earth's rotation.

If the cows were all pointing their bums in the same direction, the net effect would be nonzero. Admittedly it would be very difficult to detect the effect, but Newton's laws would still apply.

Still wrong.
http://en.wikipedia.org/wiki/Angular_momentum

I'm not sure how angular momentum disproves the effect.  If anything, it shows why there has to be an effect.  It's a simplification, but basically the cows will cause the atmosphere to pick up a tiny bit of circulation in the direction of their derrieres.  The atmosphere therefore gains some angular momentum.  Since the earth is basically a closed system, it's total angular momentum can't change, so the earth's rotation would have to change slightly to make up for the atmosphere. 

The real effect would be minuscule, however.

Geezer's post is another way of looking at it, where the earth is your system and the cow "rockets" are an external torque.

[Geezer]

Newtons laws show that there would be no net effect.

BC, think about that the next time you are in an aeroplane, because, if you are right, it ain't going anywhere.

A lot of people might have correctly assumed that I meant no effect on the Earth's rotation.

Obviously there would be effects. For example, if you were behind the cows you would probably notice. If you were smoking at the time you might notice something else too.
However neither the flatulent cows, not my air travel make much odds to the Earth's rotation.

If the cows were all pointing their bums in the same direction, the net effect would be nonzero. Admittedly it would be very difficult to detect the effect, but Newton's laws would still apply.

Still wrong.
http://en.wikipedia.org/wiki/Angular_momentum

I'm not sure how angular momentum disproves the effect.  If anything, it shows why there has to be an effect.  It's a simplification, but basically the cows will cause the atmosphere to pick up a tiny bit of circulation in the direction of their derrieres.  The atmosphere therefore gains some angular momentum.  Since the earth is basically a closed system, it's total angular momentum can't change, so the earth's rotation would have to change slightly to make up for the atmosphere. 

The real effect would be minuscule, however.

Geezer's post is another way of looking at it, where the earth is your system and the cow "rockets" are an external torque.

So, basically you are saying the atmospheric effect is a BUM STEER?

[Airthumbs (OP)]

Geezer's post is another way of looking at it, where the earth is your system and the cow "rockets" are an external torque.

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 []

[Bored chemist]

The cows' farts would push the air and the air would push the ground. After a very short while the effect would cancel out.

Because of the friction between the earth and its atmosphere, you cannot treat the two as separate systems (for long).
Since (in anything but the very short term) there's only one system, it has conserved angular momentum and its rate of rotation is conserved too.

Also, if as Geezer thinks, angular momentum is only conserved for rigid bodies, why is the classic example in all the textbooks a spinning skater who pulls there arms in and speeds up. If they pull their arms in they cannot be rigid.
It's clear that the cows' hooves push the ground, but as I pointed out earlier, so do the farts and the two effects cancel.
They have to cancel exactly because the earth, the fart, the cow, and the atmosphere are all part of one system and the momentum of that system cannot be altered by anything internal to the system.
If the cows farted into orbit then there would be an effect.

[JP]

They have to cancel exactly because the earth, the fart, the cow, and the atmosphere are all part of one system and the momentum of that system cannot be altered by anything internal to the system.
If the cows farted into orbit then there would be an effect.

They're all the same system so the total angular momentum can't change.  But parts of the system can change, which is why if the angular momentum of the atmosphere decreases, that of the earth increases.  This is exactly the effect caused by the cows.

[Geezer]

Also, if as Geezer thinks, angular momentum is only conserved for rigid bodies, why is the classic example in all the textbooks a spinning skater who pulls there arms in and speeds up.

In that situation you either treat the skater as different rigid bodies at different points in time or, as a very large number of rigid bodies, each of which has its own angular momentum, and integrate their effects at any point in time.

Oh, and the angular velocity of the skater only changed because work was done within the system of the skater.

[Bored chemist]

I don't think it makes sense to say that the atmosphere and the rock can be treated as separate systems when, as I have pointed out before, they are linked.
Have you noticed the thousand mile an hour wind at the equator?
No, that's because it isn't there. The atmosphere rotates along with the planet and that's because it's part of the planet.
As I have pointed out, there would be a temporary change but its wouldn't last.

If the cows walked East, then they would push the earth West, and, for as long as they kept walking, they would change the spin of the earth. But the thing is that when they stop they exert a force on the Earth and in doing so they push it East a bit and the Earth's spin goes back to what it was.
In the case of the "grand fart" the angular momentum transfer cannot be sustained because the farts don't keep going.

The bit about the skater doing work isn't relevant. You can change the angular velocity without doing net work. It would be odd, but it's perfectly possible.
I will now look forward to your description of the orbiting earth and the sun, with a vast gap between them somehow being a rigid system in order that angular momentum is conserved.
When you have done that perhaps you could explain how tidal drag- which kind of requires a non rigid system  (usually something sloshy) is explained in terms of the conservation of angular momentum.

Any isolated system conserves angular momentum. It does not need to be rigid. This is just as well, since no object is truly rigid anyway.

[Geezer]

In the case of the "grand fart" the angular momentum transfer cannot be sustained because the farts don't keep going.

It does not need to "keep going". The work was done, and that's all it takes to alter the state of the system.

Take the atmosphere out of it and consider what would happen if you attached a very large rocket to the moon. It would obviously cause the moon's angular velocity to increase as long as the rocket was firing. Once it stopped firing, the moon would continue rotating with a new angular velocity.

[Bored chemist]

You keep muddling up energy and momentum.

Also you missed a bit from your model

"It would obviously cause the moon's angular velocity to increase as long as the rocket was firing suff into space "

The combined angular momentum of the exhaust going clockwise is exactly the same as the anticlockwise change in the angular momentum of the moon.
The change of angular momentum of the system is still zero, and it will always be so. That's the point about conservation laws.
It's not just an approximation for rigid systems, it isn't just a figment of my imagination. It's a mathematical law, provable from first principles.
http://en.wikipedia.org/wiki/Noether%27s_theorem
It's true now, and it will still be true in the morning.

[JP]

Are we talking about permanent increase in rotation or temporary increase. 

It's true that immediately after the cows all fire, and before friction does too much, the earth will respond by speeding up, at least temporarily. 

[Bored chemist]

Unless you accept that the earth's atmosphere is part of the earth.

So, either there's no overall effect (provided that you don't think the atmosphere is part of the earth) or there's a temporary effect (which dies out rather rapidly).

Take your pick, but the idea that "It does not need to "keep going". The work was done, and that's all it takes to alter the state of the system." is wrong.

Incidentally cows generally burp more than they fart so the net effect would be the reverse of that predicted.

[Geezer]

Unless you accept that the earth's atmosphere is part of the earth.

So, either there's no overall effect (provided that you don't think the atmosphere is part of the earth) or there's a temporary effect (which dies out rather rapidly).

Take your pick, but the idea that "It does not need to "keep going". The work was done, and that's all it takes to alter the state of the system." is wrong.

Incidentally cows generally burp more than they fart so the net effect would be the reverse of that predicted.

BC, what you are obviously failing to grasp is that the mass accelerated by the cows is a consequence of work done by chemical processes. Chemical energy was converted into kinetic energy, and added to the kinetic energy of the system as a whole.

[Airthumbs (OP)]

I honestly did not think that what appeared to be such a simple question was in fact quite complicated indeed!

What if the cows all actually ran along and all farted at the same time with their hooves touching the ground?  []

[Geezer]

What if the cows all actually ran along and all farted at the same time with their hooves touching the ground?  []

We could also ask what would happen if the skater farted at the same time as she was pulling in her arms to make herself spin faster. However, that might only complicate things  []