p140w07_ct_06 - Racquetball Striking a Wall Copyright:...

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Physics 140: Winter 2007 Lecture #6 January 23, 2007 Dave Winn Racquetball Striking a Wall Copyright: Loren M. Winters Mt. Etna Andrew Davidhazy
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The plan • Use Newton’s laws to predict motions – 1: Forces change motion –2 : –3 : • If you know forces, you can find accelerations and hence motions • Last time we learned about: – Weight: an active, non-contact force – Normal force: a passive, contact force; as large as it has to be… – Today: tension and friction a m F r r = BA AB F F r r = g m W r
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Tension and force transmission F RC F CR W R F BR F RB W B Σ F R = F CR –W R –F BR = 0 Σ F B = F RB –W B = 0 So F CR = W R + F BR F RB = W B 3 rd law pairs: |F RB| =|F BR| and |F CR |=|F RC | So F CR = W R + W B For a massless rope: F CR = W B , rope transmits force
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Tension • Force transmitted through a rope • Thing on one end pulls on thing on the other: this is a third law pair • The “tension” is how hard each side pulls on the other (the transmitted force…) • When the rope is “massless”, this transmission is perfect • “Massless” means mass of rope is << than others in the problem…
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In the 17th century, Otto von Güricke, a physicist in Magdeburg, fitted two hollow bronze hemispheres together and removed the air from the resulting sphere with a pump. Two eight-horse teams could not pull the halves apart even though the hemispheres fell apart when air was readmitted. Suppose von Güricke had tied one team of horses to one
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This note was uploaded on 04/04/2008 for the course PHYSICS 140 taught by Professor Evrard during the Fall '07 term at University of Michigan.

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p140w07_ct_06 - Racquetball Striking a Wall Copyright:...

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