1DISCUSSION PROBLEM [4.1]:Why does a wire stretched between two posts always sag in the middle no matter how tightly it is stretched?DISCUSSIONPROBLEM [4.1]: answer ...Assumewire 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.,rrFF12=... but there are no vertical components of rF1and rF2to compensate rwand produce no net vertical force. Therefore, our assumption that the wire is horizontal is incorrect; clearly, to compensate for rw, rF1and rF2must have vertical components. Therefore, they must “slope upward”, i.e., the wire must sag in the middle, viz:rF1rF
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