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Viewing Message ``Re: Potential Energy and Conservation of Energy'' by wmccutchen on 2007-12-02 12:42:02 How about a more realistic example, such as a baseball pitcher?  He is like the Earth, and the ball is like the moon.  When his arm rotates about his shoulder holding the baseball, there is a tension due to equilibrium of centrifugal and centripetal force.  Although it is often said that centrifugal force is fictional, and only centripetal force is real, what matters is that there is an opposition and an equilibrium and a tension.   This tension is potential energy, like a stretched rubber band.  The centripetal force (= mv^2/r , where m is the mass of the ball, v is its tangential velocity during the pitch, and r is the distance from the ball to the shoulder) constrains the ball from flying off.  When the ball is released, the opposing (fictional??) centrifugal force disappears, but the muscles are still stretched, so they contract suddenly and crunch the shoulder.  The potential energy becomes ball kinetic energy and a radial compression. Should the Moon fly off, e.g. hit by an asteroid, would we have earthquakes due to the consequent compression of the Earth? [ reply | up | top ] Interact reply

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