If you weigh 200 lb at the Equator, how short would a day have to be to weigh 100 lb?

Question

The spin of the Earth tends to pull us away from the surface but gravity is stronger. How much faster would the Earth have to spin to weigh 100 lb?

Answer 1

Quite a lot. In order to weigh zero at the equator, you would need to be moving as fast as a satellite in low earth orbit -- about 17,500 miles per hour. Since the centrifugal force goes as the square of the velocity, to lose half your weight would need to reduce the speed by sqrt(2), to about 12,400 mph. If you are going east, subtract the earth's surface speed to get 11,300 mph. Or, the earth would have to speed up by a factor of 12. A fascinating novel exploring this idea is:

Answer 2

19.5 seconds.