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discussion_problems4

discussion_problems4 - DISCUSSION PROBLEM[4.1 answer Assume...

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1 DISCUSSION PROBLEM [4.1] : Why does a wire stretched between two posts always sag in the middle no matter how tightly it is stretched? DISCUSSION PROBLEM [4.1] : answer ... Assume wire is horizontal and consider a small section of wire in the middle: As the wire is in equilibrium, i.e., no motion, then there is no net force, i.e., r r F F 1 2 = ... but there are no vertical components of r F 1 and r F 2 to compensate r w and produce no net vertical force. Therefore, our assumption that the wire is horizontal is incorrect ; clearly, to compensate for r w , r F 1 and r F 2 must have vertical components. Therefore, they must “slope upward”, i.e., the wire must sag in the middle, viz: r F 1 r F

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