Tetherball!
Entry posted by DavidStack
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Continuing with the physics of recreational sports, I'd like to talk about the physics of tether ball, a sport I'm not quite as good at. But, tether ball clearly demonstrates centripetal motion, and is very interesting to delve into. A player will hit the ball with a horizontal force F. Neglecting air resistance, this will temporarily be the only force on the ball, and will equal the mass of the ball times the acceleration of the ball. Centripetal acceleration equals (v^2)/r, so, given that the mass of a tetherball is about .27 kg, and the rope (which is the radius in this situation) is about 2.25 m, F = (.27 * v^2) / 2.25. Given this equation for velocity, a player can figure out how to beat his or her opponent. If a player know that his or her opponent cannot return a ball traveling greater than 10 m/s, he or she knows to hit the ball with at least an F = (.27 * 10^2) / 2.25, or F = 12 N, assuming the rope can sustain this force. So, even though air drag has an affect on the ball, and it is very hard to figure out how to hit something with a certain force in newtons, the physics of centripetal motion helps one to attain a better knowledge of how tetherball works.
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