A light rigid rod is suspended from the ceiling and is spinning freely about the vertical axis at an angle θ with the vertical as shown. Two small identical masses are attached to the midpoint and to the bottom end of the rod. Find the angle between the horizontal and the force exerted by the rod on the mass attached to the midpoint.

Let m be the masses attached to the midpoint and to the bottom end of the rod with length L, and ω – the angular speed about the vertical axis, which is obviously related to L and θ.

If we neglect the mass of the rod, it is easy to find this relation having in mind that the resultant torque on the pair of masses m must be zero:

L2mgsinθ+Lmgsinθ=L22L2...
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