Physics Question #2968

Francis, a 40 year old male from Ottawa asks on October 6, 2005,

When a ball is rotated at the end of a string in a horizontal circle (parallel to the ground) what balances the force of gravity to prevent the ball from falling straight down? I understand that inertia balances the tension of the string (the centripetal force) in the horizontal plane, but I am unsure of how to describe what is doing the balancing of gravity in the vertical plane.

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The answer

Jess Brewer answered on October 7, 2005

The circular path of the ball may be horizontal, but the string isn't. It drops a bit from the pivot point to the ball, and so the "centripetal" force is actually part horizontal and part vertical. The vertical part balances the downward force of gravity.

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