来自《耶鲁大学开放课程：基础物理 第9集 第9集》
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and the useless part,这个没用的分力 -
which is trying to pull the rod off the hinges,企图将把手从铰链上拉下来 -
is going to be balanced by a force from the hinges,它与铰链对它的作用力相抵消 -
because the rod is a rigid rod,因为这个杆是个刚体 -
it's not going to move.所以不会移动 -
But the one perpendicular to the rod can, in fact,但垂直方向对杆的作用力 -
turn the rod without affecting the rigidity.会使杆转动 同时不会改变杆的刚性 -
So, we need an extra factor here,因此我们在这里要加另外一个量 -
which is sin(θi),就是 sin(θi) -
where θi is defined as follows.θi 是这样定义的 -
If you're at a point Ri,假设一个质点位于 Ri 处 -
and you apply a force F that way,对它施加一个这个方向的力 F