2007-03-15 06:46:37 · 10 answers · asked by Anonymous in Science & Mathematics ➔ Astronomy & Space
The short answer to your question is never! the Moon rate of motion decreases the greater its orbital distance becomes. The Moon will eventually move far enough from Earth that its orbit will stabilize and increase no further. Theoretically, the Moon's orbit will eventually stabilize at a distance 1.6 times what it is today in about 15 billion years. I say theoretically since our current understanding of the Sun is that it will expand into a red giant in only five billion years or so and destroy both the Earth and Moon in the process. The force of gravity on the moon is a fraction of the gravity on the earth, so the moon would not be able to crush the earth to inself. The reason the Moon's orbital distance from Earth is gradually increasing is due to the influence of the tides. Tides on Earth are created by the gravitational influence of both the Moon and the Sun that tug on the planet and cause it to bulge outward slightly at the equator. The majority of this equatorial bulging is actually due to the rotation of the Earth about its axis. This rotation raises the equator about 23 kilometers, or 0.4% of the Earth's radius, higher than it would be if the Earth did not rotate. The planet's shape is further deformed by the gravitational pull of the Moon. While the solid surface of the Earth is distorted by only a few centimeters, the primary effect is on the oceans that rise by a few meters. The tidal effect is not only causing the Moon to move further away from Earth but is also slowing the Earth down. While the tidal bulge leads the Moon and pulls it forward, the Moon also exerts a gravitational attraction on the tidal bulge that pulls it backward. As the ocean waters are pulled across the ocean floor, friction is created that slows the Earth's rate of rotation about its axis. This effect slows the Earth's rotation by 0.0018 seconds, or about two milliseconds, per century. This same phenomenon continues today as the tides slow Earth's rate of rotation. If allowed to continue to its conclusion, the length of a day on Earth and the time it takes for the Moon to orbit the Earth will equalize to about 55 days. Once that occurs, the Earth will always present the same face to the Moon just as we on Earth can only see one side of the Moon. The tidal bulge that now leads the Moon will instead point directly at the Moon and the Moon will stop moving further away from Earth. This process is known as tidal locking and is a common occurrence between other bodies in the solar system.
2007-03-18 12:41:26 · answer #1 · answered by Byzantino 7 · 3⤊ 0⤋
You can ask the same about the earth and the sun, or any other planet and the sun. It's because, like the earth around the sun, the moon has it's own velocity which wants to escape from the earth, but, the earth's gravity is too strong to let the moon go.
Think of it as you and a little kid both holding each end of a rope.. you're both tugging on each opposite end, but you are stronger... so he isn't going anywhere and since he tugging away, he won't go into you.
2007-03-15 06:53:10 · answer #2 · answered by Andy 1 · 0⤊ 0⤋
Actually, it *is* moving away from Earth... a few inches every decade. The tidal bulge around Earth accellerates the moon just slightly - with the result being our day is getting longer, and the moon is moving further away.
But, in general - the speed of the moon at the distance away from Earth keeps it in orbit. If it were to suddenly gain speed, it would be stripped away from Earth; if it were to suddenly lose speed, it would fall in toward Earth.
2007-03-15 07:16:30 · answer #3 · answered by quantumclaustrophobe 7 · 1⤊ 0⤋
Quantum gave you the best answer. The moon IS drifting away from the earth, due to tidal friction. This is known as lunar recession, and the rate was accurately measured with lasers after astronaughts set mirrors up on the surface of the moon.
3.8 cm per year is the current measured recession rate.
The site below may answer more of your questions.
2007-03-15 09:11:23 · answer #4 · answered by Anonymous · 0⤊ 0⤋
The moon is moving at a pretty fast rate. This speed keeps it from falling to earth. It actually is moving away from us at a very slow rate, a few inches a year. So, in fact, it IS drifting away from earth.
2007-03-15 07:37:18 · answer #5 · answered by Anonymous · 0⤊ 0⤋
The moon is in the earth's orbit, it is held there because of some gravity and the Earth's orbit but there isn't enough gravity 'out there' to make it smash into the Earth if you like...
Lorna
2007-03-15 06:50:41 · answer #6 · answered by ? 6 · 1⤊ 0⤋
The moon is held inplace by it's gravitational interaction with the earth and its orbital velocity. It is drifting away at about 1.5 inches a year.
2007-03-15 06:52:08 · answer #7 · answered by Gene 7 · 1⤊ 0⤋
In uniform circular motion, the force points towards the center of the circle (and in the moon's case, gravity is the force) and this causes the circular rotation.
2007-03-15 06:52:14 · answer #8 · answered by Pfo 7 · 1⤊ 1⤋
See Kepler's 3-laws. It is in orbit - just like earth to the sun.
2007-03-15 07:29:45 · answer #9 · answered by ericscribener 7 · 0⤊ 0⤋
I suspect you might be quite young, or live somewhere where education is not very good. But even so, I suggest you go into
http://www.wikipedia.com
and look up Kepler.
That will tell you all about orbital physics.
2007-03-15 08:43:21 · answer #10 · answered by nick s 6 · 0⤊ 1⤋