It is actually called orbital velocity: v=sqrt(gR), where g is the acceleration of gravity 9.8 m/s^2, and R is Earth's radius (about 6370 km). By plugging into this equation you get v = 7.9 km/sec - if the Earth would rotate with this speed at the equator, the centripetal acceleration would be equal to the acceleration of gravity g and we would hover over Earth' equator, orbiting Earth together with Earth itself. This would happen if a day was 1.6 hour long.


Anyway, place a pen parallel to local g (which already includes centripetal acceleration, by the way) and try to find out which direction it falls.

Hint: use the solution of the equation governing pen's motion: exponential amplification of initial angle.

• and YOU DON'T - carefuluniverse - December 5, 2001 - 02:25 UTC