Earth's rotation

[Tommyb323]

If the earth were to revolve faster on its axis than it does today, what would happen to its shape?

[Clanad]

The measured bulge at the equator would likely increase. The amount of the increase would be somewhat dependent on the speed you would propose. Early on in Earth's history (pre-Cambrian) it's believed the rotational period was as little as 15 hours per day rather than the near 24 hour period today. That increased speed did not have a significant affect on the shape of the Earth.
Significantly, although a gas giant, Jupiter rotates once each 9 hours (approximately) and still retains a spheroid shape. The most damaging effect of increased rotational speeds on Earth would probably be the increase in surface wind speeds. Some scientists believe the Earth's early wind speeds due to the faster rotation could have been in the range of 750-1000 mph. However, Jupiter's maximum speeds are around 200 mph at the equator, so estimates of Earth's early history may be somewhat less. We do know that Saturn, Uranus, and Neptune also have wind systems, and their winds exceed the speeds observed on Jupiter. No one seems to know why as yet...

[Pebbilita]

Clanad... so why did the earth speed up? and is it still speeding up? Did the change in speed have any affect on gravity?

[Clanad]

Actually, I see I didn't clearly state the earth's rotation has slowed... speed has nothing to do with gravity, which is a centripetal force by the way. The rotational force is centrifugal.
The Earth's oblate spheroid shape was more pronounced when it was younger and spinning faster. One source indicates that it currently bulges 27 miles at the equator, whereas it was at least 15% more pronounced early on.
There are, apparently, a number of reasons the planet has been slowing, such as tides, solar winds, geomagnetic storms, and gravitational effects of the moon and other planets and finally entropy. The planet was set in motion, as was the rest of the solar syatem and, indeed, the entire universe, as the galactic and planetary bodies coalesced from the original creation event some 14.5 billion years ago (the earth is estimated to be about 4.5 billion years old)....

[JudgeJ]

The principle reason for the Earth�s rotational speed decreasing is the tidal effect of the moon. As the earth rotates the gravitational forces imposed by the moon pull the earth out of shape, elongating it in the direction of the moon�s gravity. This happens to any body with an orbiting satellite but can be seen quite clearly on Earth. With its surface predominately covered in water it manifests itself by the twice daily rise and fall of the "tides".

Being pulled out of shape slows the earth down. (Try spinning a ball and see how long it takes to come to rest. Then stick a lump of Plasticine on each side. You will see it takes far less time to stop spinning). However, since the total energy in the earth/moon system must remain the same, the moon is actually speeding up in its period of orbit around the Earth (currently about 28 days).

Eventually the earth and moon will become �tidally locked�. The period of the Earth�s �day� (the time it takes to revolve once on its axis) will be the same as the lunar �month� (the time it takes the moon the orbit the Earth). The same part of the earth will then always face the moon. This has already happened to the moon � it is much less massive than Earth and the Earth�s tidal effect upon it is far greater. The same face of the moon always faces Earth and we can only see one side. It has also happened to the planet Mercury in relation to the Sun.

This will have a profound effect upon the Earth as the rise and fall of the tides will slow and eventually cease. The water level in the seas will then be constant for any given point on the Earth.