Monday, May 4, 2015

newtonian mechanics - Accelerating an elevator


A person is standing on a weighing scale in an elevator in upward acceleration.


Let $N$ be normal reaction force exerted by the weighing scale to the person (upward).


It is known that the person will experience a normal reaction force ($N$) larger than his own weight (larger reading on the weighing scale). While $N$ is equal, but in opposite direction, to the force that the person exerts to the weighing scale due to action-reaction pair (the person and the weighing scale). That means other than the person's weight, there should be an extra force exerting to the weighing scale downward ($A$).


So $-N$ (upward)$ = mg + A$ (downward). I can't figure out where does $A$ come from?




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