Importance of Earth’s rotation
Craig Lindsay, of Totara Park, asked:
What would happen if the earth either stopped rotating or slowed down drastically. Would the oceans fly off into space?
Alan Gilmore, an astronomer at the University of Canterbury’s Mt John Observatory, responded:
It is Earth’s gravity that pulls everything towards its centre.
Rotation has nothing to do with holding things onto the earth.
The planet Venus has a very slow rotation but holds onto a deep atmosphere. So if the earth stopped rotating, then gravity would still hold things down as before.
But if Earth suddenly stopped spinning, there would be chaos.
At the equator, everything is moving eastwards at more than 1600kmh. At New Zealand’s latitude, the speed is about 1200kmh. If the spinning suddenly stopped, then anything loose or fluid would continue moving, just as a sudden stop in a vehicle makes everything lurch forward. Oceans, lakes and rivers would slop up against their eastern shores as the water tried to keep moving. The air would take some time to slow down too.
If Earth slowed down a bit, then days would get longer. Also the time between tides would get longer. The Earth’s spin is in fact slowing down due to the drag of the ocean tides. Our day is lengthening by around 2 milliseconds (0.002 second) per 100 years. The spin energy (angular momentum) lost by the earth makes the moon’s orbit bigger by 38mm per year.
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