Bolt a metal rod to the end of the blade of a jig saw so that the rod can pivot in one plane. Here is a sketch of the object:
------------- | ^^^^^^^^^^_|_______________________ | _________________________| | ___________| -------------- saw handle blade metal rod moves <---> pivots in the plane of the picture
In the picture the rod and blade are facing to the right. However, notice that with the motor off, since the rod can pivot, if it is not held in this position, it will fall and point downward.
What would you expect to happen if with the motor running you point the object so that the rod and the blade face directly upward? Will the rod fall to point downward? Will it continue to point upward direction? Or will it instead point at some angle from the vertical? Consider the case in which the length of the rod is much larger than the gravitational acceleration over the square of the frequency of the jigsaw blade.
This puzzle is by no means easy. However, since it is not too hard to visualize what is happening physically, I wanted to give people a chance to at least think about the situation before I say what happens and why. I will post an answer in a few days. Please do not post an answer until then.