Re: Question about free fall versus rotating bodies.

Hi Chris

Your analysis of the gravitational forces I agree with. Let us look at the second.

I suspend a massless bar from above with a support at each end. I add a charge to the bar slightly off center. At this point there are no forces acting on the bar, up or down. I apply an electric field to the system. There is now a downward force on the charge, which is also applied to the bar. The charge is forced downward in the same direction as the electric field. The supports are released. The bar moves downward due to the force from the electric field on the charge. For the bar to rotate there must be an uneven force on the bar. The charge moves downward in a straight line. The only force on the bar is downward so the bar does not rotate. Since the bar has no mass it has no inertia to resist the change in motion so the force on the bar is vertical.

What would happen in an actual experiment? Let's consider a plastic rod, suspended by nonconducting threads. The threads are so small to be considered massless for the experiment. I apply a net charge to the rod. The charge will distribute itself evenly over the rod. The downward forces, in an electric field, will be gravity and the electric force on the charges. Both will be vertical. The bar will fall evenly downward when released. Reverse the charge's sign and we can envision the case when gravity and the electric force balance and the bar will stay stationary. Remove gravity and mass, if possible and the remaining force will cause the bar to accelerate in the vertical direction without rotation. I hope that this helps. As I see it, there will be no rotation by the bar in your example.