how the earth is rotating still without any external forces?

Answer 1

God

Answer 2

Best explanation i found:

First, the investigation of Earth rotation is not a simple matter. The reason is that the Earth departs from a perfect sphere (thus, for example, one cannot simply calculate ONE moment of inertia - say 0.4MR^2 for a sphere - but must reckon separate "axial" and "equatorial" moments since the Earth is oblate)

To be specific, the equatorial moment of inertia is roughly 1/300 of the axial moment. This may seem like an insignificant difference - but when one is dealing with extremely small measures, times, it emerges as important.

Second, the changes in Earth rotation are not uniform across the board- though true, there is a general long term trend to slow down - arising from the tidal breaking of the Moon.

Let's go into this a bit more - prior to me giving examples of how the Earth's rotation can get *faster*.

The Earth rotates faster than the Moon moves in its orbit. Because the tides are linked to the more slowly moving Moon, they act by friction as a brake on Earth's rotation,
gradually slowing it down. (It is estimated by 0.0007 seconds per century)

The angular momentum lost by the rotating Earth in this process is transferred to the Moon's angular momentum. Thus, the Moon is accelerated in its orbit, causing it to slowly spiral outwards...away from Earth. The day and month are thus lengthening at different rates.

Calculations have actually been retro-worked to show how the length of month differed when the Moon was much closer to Earth in the past. For example, when the Moon was only 16,000 km away (10,000 miles) the month was approximately seven mean solar days long.

Similar calculations based on the conservation of angular momentum also allow us to project into the future. Thus, about three billion years hence, the day and month will be equal - about 47 of our present days long - and the Earth will always turn the same face towards the Moon.

Now, let's get back to exceptions to day lengthening. These mostly arise from sporadic tectonic events such as earthquakes- or more recently the Indian Ocean tsunami.

Recent computations of the seismic moment arising from the generating Earthquake have determined that the length of day briefly *decreased* by about 2.68 micro-seconds. (This would be analogous to a spinning ice skater briefly pulling her arms in closer to herself).

Then too, cumulative earthquakes over magnitude 5 (of which there have been 21, 600 since 1977) have an overall tendency to make the whole planet rounder and more compact in all directions, thereby shortening the length of day.

It is also theorized that mammoth solar flares - by expanding the atmosphere- can also contribute to a change in the rotation rate. How exactly remains to be worked out, but no doubt friction (creating drag) between atmosphere and planetary surface might play a role.

All this is to try to make you aware that changes in the Earth's rotation arise from multiple causes, sources and can alter in either the positive or negative direction. Again, the *general* trend is for slowdown - owing to the reasons given earlier

Answer 3

y do u think there is no external force
the suns gravity offers centripetal force to the earth...and so it keeps on rotiting
moreover there is no moment of inertia to stop it from rotating and so kept rotating since the time of bing bang

Answer 4

by the centrifugal force