
#1
Aug2211, 12:43 PM

P: 54

suppose there are two bodies,one revolving in an orbit around the other[like the earth moon system]Differences in orbital and axial rotation of a small body results in a torque applied on it by the larger body. This results in the smaller body being tidally locked.
THEN WHY ISN'T THE EARTH TIDALLY LOCKED WITH THE SUN?WILL IT EVER BE? 



#2
Aug2211, 01:52 PM

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There hasn't been enough time. Even the Moon, which has ~twice the tidal effect on the Earth as the Sun does hasn't had enough time to tidally lock the Earth it.




#3
Sep1511, 12:55 PM

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#4
Sep1511, 01:17 PM

P: 1,784

Will the earth and sun ever be tidally locked?
As Janus says, the moon has ~twice the tidal effect as the sun, so it would seem unlikely until the moon's orbit moves far enough away from earth that the sun has a greater effect or that the period of lunar orbit equals one earth year.




#5
Sep1511, 01:58 PM

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#6
Sep1511, 02:07 PM

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[tex]\frac{\omega a^6 I Q}{3GM^2k_2 R^5}[/tex] Tidal locking takes time to occur. The factors include the initial rotation speed of the body, its distance from the other body, Its moment of Inertia, the Mass and radius of the body it is orbiting, plus a couple of coupling factors. I mentioned the Moon because its tidal effect on the Earth is larger than the Sun's, so if not enough time has passed for the Moon to slow the Earth's rotation to match its orbit, then definitely not enough time has passed for the Sun the tidally lock the Earth to it. 



#7
Sep1611, 07:41 AM

P: 765

Ummm...The moon is tidally locked.
The above equation is a good one though. 



#8
Sep1611, 08:30 AM

P: 54

Thank you very much!!!




#9
Sep1611, 09:01 AM

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#10
Sep1611, 09:12 AM

P: 765

Not to sound rude, but: so? The earthmoon and earthsun systems are independent (barring the rotational effects the moon has on the earth). There's no sense in comparing the two.
Besides, the question is whether the Earth will become tidally locked to the Sun. In this case, the earth is the satellite and the sun is the primary. In the earthmoon, the earth is the primary and the moon is the satellite. The OP asked whether or not the earth will be tidally locked to the Sun, not the other way around. 



#11
Sep1611, 10:37 AM

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#12
Sep1611, 10:43 AM

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#13
Sep1611, 11:09 AM

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It is This tidal force acting on the Earth which would cause it to lock with either the Earth or Moon. Since the Moon exerts the greater tidal force on the Earth, It would be the first to tidally lock the Earth to it. Actually, if you look at the formula I gave for the time for tidal locking to occur, you will note that it increases by the distance between the bodies (a) to the power of 6, and decreases by the mass of the acting body by only the square of the mass. So 400^6/27210884^2 = 5.53, meaning that it would take ~5.5 times longer for the Sun to lock the Earth to it than it would for the Moon to lock the Earth. 



#14
Sep1611, 11:39 AM

P: 765

I see what you are saying. I stand corrected.




#15
Sep1611, 12:13 PM

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#16
Sep1611, 12:49 PM

P: 765

The equation above describes the time required in those conditions to attain tidal locking.
It's not a matter of assumptions, really. It's a matter of physics, and I'm sure the equations were derived painstakingly and are very long. 



#17
Sep1711, 10:28 AM

P: 80




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