# gravity

Philippines
April 11, 2007 1:33pm CST
Is gravity around the planet constant? If you have a spinning ball and put a penny on it, it will be thrown off at the equator but not at the pole?
2 responses
@jamie622 (508)
• India
11 Apr 07
The example of coin being thrown away at the equator and no at the poles has nothing to do with gravity of the planet . YOu place the ball on the equator or the poles does not matter at all . The position of the penny on the ball is what matters . If you place it on the poles of the ball it won't fly away but if you place it on the equator of the ball it would . In the first case when it is placed on the poles the centrifugal force is zero since the radius is zero while in second case the radius is equal to the radius of the ball and the centrifugal force is non zero causing the penny to fly away . To answer your question whether gravity around the planet is constant or not , it is not constant . Gravity depends on the distance of the point from the centre of earth , since earth is no a perfect sphere it differs from place to place .
@jamie622 (508)
• India
11 Apr 07
The example of coin being thrown away at the equator and no at the poles has nothing to do with gravity of the planet . YOu place the ball on the equator or the poles does not matter at all . The position of the penny on the ball is what matters . If you place it on the poles of the ball it won't fly away but if you place it on the equator of the ball it would . In the first case when it is placed on the poles the centrifugal force is zero since the radius is zero while in second case the radius is equal to the radius of the ball and the centrifugal force is non zero causing the penny to fly away .