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Author Topic: why is the Moon tidally locked with the Earth?  (Read 3223 times)

Offline lunar11

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why is the Moon tidally locked with the Earth?
« on: 22/08/2009 11:47:19 »
I know we only see one side of the Moon because the time it takes to orbit the Earth once is the same as the time it takes to rotate once. But why is this the case?


 

Offline RD

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why is the Moon tidally locked with the Earth?
« Reply #1 on: 22/08/2009 12:26:47 »
The moon is not truly spherical: it has a slight bulge which points towards the Earth.
The bulge was created by gravitational pull of Earth when the now solid moon was mostly liquid. 

Tidal locking is a bit like the front wheel of an upside down a bicycle, (stay with me).
When the wheel is spun it always comes to rest with the valve at the 6 o'clock position.
The valve makes that bit of the wheel heavier and point towards Earth.
 

Offline wanhafizi

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why is the Moon tidally locked with the Earth?
« Reply #2 on: 22/08/2009 15:06:34 »
The moon is not truly spherical: it has a slight bulge which points towards the Earth.
The bulge was created by gravitational pull of Earth when the now solid moon was mostly liquid. 

Tidal locking is a bit like the front wheel of an upside down a bicycle, (stay with me).
When the wheel is spun it always comes to rest with the valve at the 6 o'clock position.
The valve makes that bit of the wheel heavier and point towards Earth.

Is it true that there was a collision which ripped off a part of the earth? ... and therefore voila!, a moon. Because it was once from the same origin, it rotates the same way as the earth does.


 

Offline RD

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why is the Moon tidally locked with the Earth?
« Reply #3 on: 22/08/2009 15:34:39 »
Is it true that there was a collision which ripped off a part of the earth? ... and therefore voila!, a moon.
 Because it was once from the same origin, it rotates the same way as the earth does.


That doesn't explain why moon rotates so the same side always faces earth, (tidal locking).

Seen from the Earth the moon wobbles back and forth, consistent with my bike wheel valve explanation.
« Last Edit: 22/08/2009 15:37:15 by RD »
 

lyner

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why is the Moon tidally locked with the Earth?
« Reply #4 on: 23/08/2009 17:23:16 »
The point which has not been made on this thread is that, without energy loss, the bulge on the Moon would be wobbling a lot or spinning- for ever. It has settled down in the present, almost stationary, condition because the oceans and other slightly moving masses on both bodies are absorbing this energy and keeping things stable.
This also accounts for the Moon's orbit getting bigger and the Earth's day getting longer.
 

Offline Nizzle

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why is the Moon tidally locked with the Earth?
« Reply #5 on: 24/08/2009 10:57:18 »

This also accounts for the Moon's orbit getting bigger and the Earth's day getting longer.

So at some point in the future, we'll lose our moon?
 

lyner

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why is the Moon tidally locked with the Earth?
« Reply #6 on: 24/08/2009 11:35:22 »
The ultimate condition would be with Earth and Moon facing each other all the time and a huge orbital separation. (All three angular velocities being the same.)
Of course, the influence of some other planet or the Sun would have long since disturbed the situation.
 

The Naked Scientists Forum

why is the Moon tidally locked with the Earth?
« Reply #6 on: 24/08/2009 11:35:22 »

 

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