Gravitational effects of Earth and Moon.

[paige123]

If the gravitational pull of the Moon is only a third that of the Earth then,Why doesn't Earth draw the moon toward itself ?.We know the Moon has an effect on the tides of the oceans and seas on Earth with only a third of the gravity, so why doesn't it work the other way round. In fact scientists insist in the notion that the Moon is actually moving away from the Earth by a measurable amount every year. Cheers Paige123
P.S I really must get out more.

[Clanad]

From our friends at Ask an Astonomer...
"...The Moon raises tides on the Earth. Because the side of the Earth that faces the Moon is closer, it feels a stronger pull of gravity than the center of the Earth. Similarly, the part of the Earth facing away from the Moon feels less gravity than the center of the Earth. This effect stretches the Earth a bit, making it a little bit oblong. We call the parts that stick out "tidal bulges." The actual solid body of the Earth is distorted a few centimeters, but the most noticable effect is the tides raised on the ocean.

Now, all mass exerts a gravitational force, and the tidal bulges on the Earth exert a gravitational pull on the Moon. Because the Earth rotates faster (once every 24 hours) than the Moon orbits (once every 27.3 days) the bulge tries to "speed up" the Moon, and pull it ahead in its orbit. The Moon is also pulling back on the tidal bulge of the Earth, slowing the Earth's rotation. Tidal friction, caused by the movement of the tidal bulge around the Earth, takes energy out of the Earth and puts it into the Moon's orbit, making the Moon's orbit bigger (but, a bit pardoxically, the Moon actually moves slower!).
This same process took place billions of years ago--but the Moon was slowed down by the tides raised on it by the Earth. That's why the Moon always keeps the same face pointed toward the Earth. Because the Earth is so much larger than the Moon, this process, called tidal locking, took place very quickly, in a few tens of millions of years"

[NiceCupOfTea]

They're stuck in a moving stasis, baby. Can't live without it (us) can't move on while with us (it) - typical man / woman thing. Luckily for us the orbit has reached equilibrium, so unless a nasty big meteorite hits our moon, it's here to stay. Actually, it wouldn't have to be that big allegedly. From a very unverifiable source, 400 metres in width would do it, but most others put it at a much larger chunk of hunk to distract our beautiful night lady, so I'm not panicking yet.

[Rev. Green]

Does the first part of your question mean "Why doesn't the Moon fall to Earth?"
The Moon does fall towards the Earth! It is pulled down by the Earth's gravity. Luckily, the amount that it falls is almost exactly equal to the distance that it would move away from the Earth if there were no gravity. (Without gravity, the Moon would travel into space in a straight line.) So, on balance, it keeps about the same distance away.

[R1Geezer]

Yes the moon is falling to Earth, in fact it is in free fall very similar to a skiydiver falling. However it can never reach Earth because it is moving at great speed forward and thus the ground falls away. It';s the same thing that keeps artificial sattelites in orbit, they are moving at thousands of miles per hour and gravity is pulling them down but they are missing the Earth and thus are in constant freefall.

[Teddio]

The attractive force of the Moon on the Earth is equal to the attractive force of the Earth on the Moon.

[R1Geezer]

WTF are you on about teddio, go back to chatterbank, this is grown up talk!

[Clanad]

Actually, the moon is moving away from the earth... but very slowly. One estimate includes this tidbit: "...It is expected that in 15 billion years, the orbit will stabilize at 1.6 times its present size, and the Earth day will be 55 days long equal to the time it will take the Moon to orbit the Earth. Of course, in less than 7 billion years, the Sun will have evolved into a red giant star and engulfed the Earth-Moon system, thereby incinerating it!

[Mortartube]

"Of course, in less than 7 billion years, the Sun will have evolved into a red giant star and engulfed the Earth-Moon system, thereby incinerating it!"

Damn, I'd better get the washing in then.

[mibn2cweus]

Just for the record, the Moon's contribution to the mutual gravitational attraction between Earth and Moon is less than 1/80 of that of the Earth.

[dustypuss]

at last I will be able to turn the heating down