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Jean-Louis
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Earth's velocity is 30 km/s.
What would be Earth's velocity without the moon ? What's the formula?
What would be Earth's velocity without the moon ? What's the formula?
Jean-Louis said:Earth's velocity is 30 km/s.
What would be Earth's velocity without the moon ? What's the formula?
YesJean-Louis said:Would Earth spin much faster without its orbiting moon ?
The pull of the moon, puts the brakes on Earth's daily rotation, right ?
Is there a way to calculate how fast the Earth would be spinning on its axis, If we didn't have the moon ?
[PLAIN said:http://en.wikipedia.org/wiki/Tidal_acceleration][/PLAIN]
620 million years ago: the day was 21.9±0.4 hours
If the moon "just disappears", why would it leave behind its angular momentum? I know that angular momentum is conserved, but so are a lot of other things whose conservation would be violated by the moon "just disappearing.Jean-Louis said:if L means angular momentum.
L(no moon) = L(earth+moon) + L(moon) + L(moon's orbit)
If we toss in L=Iw, hence we can figure out how fast Earth would be spinning.
Ian said:..
Conclusion - it can not be 'lunar' tidal forces that are retarding the Earth 's rotation.
Three body problem? nah bruv, common sense problem more like.
Ian said:Mmm, if the moon has the ability to slow down the Earth's rotation due to its mass then by the same token the Earth must have a similar effect on the moon's rotation.
Now, the moon does rotate, but at a rate that makes it appear stationary to an observer on the earth. Therefore by the thoughts above the Earth ought to influence the lunar rotation and slow it down, this seems common sense to me, but no-one has ever seen the dark side except till the space age. The moon's rotation is obviously static, but the Earth's is changing.
Conclusion - it can not be 'lunar' tidal forces that are retarding the Earth 's rotation.
Three body problem? nah bruv, common sense problem more like.
That would be true if objects were point masses, but they aren't.YellowTaxi said:I don't see what difference the orbital speed or rotation/spin of anything makes to this. Only a change in the centre of mass is going to affect the trajectory.
the moon does rotate, but at a rate that makes it appear stationary to an observer on the earth. ... tidal
Agreed, I was just pointing out that tidal stresses on the Earth aren't going to affect the rate of rotation of the moon.NoTime said:Tidal stresses affect not only bodies of water but, the crust moves as well.
russ_watters said:That would be true if objects were point masses, but they aren't.
Well, the moon does still oscillate back and forth relative to it's tidal-locked position. There is a complicated interaction of effects there, but part of it is an oscillation due to the force component responsible for tidal locking.NoTime said:Tidal stresses affect not only bodies of water but, the crust moves as well.
If the moon rotates relative to the Earth, not the case now.
There is more to Newton's gravity than just that.YellowTaxi said:No it's true for any object, not just point masses. You don't need to know the distribution of mass on a planet to use Newton's Law of gravity do you, - You only locate it's centre of mass and treat it just like a point mass. Newtons gravity law would be incredibly complicated otherwise wouldn't it
True, but in this case, the simplification simplifies-away the effect that we're discussing.And any physics problem is vastly simplified by analysing the motion of the centre of mass of the system.
No, it is more complicated than you realize. See all of the above posts about tidal locking. If what you were saying were true, there'd be no such thing as tidal locking. Heck, there'd be no such thing as tides if we could only consider the objects as point masses! To calculate tidal forces you, at the very least, need to consider a dumbell-shaped object with two point masses.The solution is actually very simple and I think you people are making it sound very difficult. It's not.
Resulting torque: Since the bulges are now displaced from the A-B axis, A's gravitational pull on the mass in them exerts a torque on B. The torque on the A-facing bulge acts to bring B's rotation in line with its orbital period, while the "back" bulge which faces away from A acts in the opposite sense. However, the bulge on the A-facing side is closer to A than the back bulge by a distance of approximately B's diameter, and so experiences a slightly stronger gravitational force and torque. The net resulting torque from both bulges, then, is always in the sense which acts to synchronise B's rotation with its orbital period, leading inevitably to tidal locking. [/qutoe]
http://www.answers.com/topic/tidal-locking
YellowTaxi said:No it's true for any object, not just point masses. You don't need to know the distribution of mass on a planet to use Newton's Law of gravity do you, - You only locate it's centre of mass and treat it just like a point mass. Newtons gravity law would be incredibly complicated otherwise wouldn't it
YellowTaxi said:That can't be true DH,
the Earth plus the Moon is definitely not a sphere, but their centre of mass can still be treated as a point mass moving on a perfect ellipse around the Sun.
D H said:The Earth-Moon center of mass can be approximated as moving in an ellipse. Even if the Sun, Earth, and Moon were the only objects in the universe, this approximation would not be exact.