# Orthogonal angle with respect to all inertial frames?

1. Feb 24, 2010

### e2m2a

Here is a thought experiment that I cannot resolve. Maybe someone smarter than I can do this. Suppose we have a long, thin rod rotating in the counter clockwise direction. The rod rotates around an axis which is connected to one end of the rod. The axis is attached to a second object which we will denote as the slider. The slider can slide along a straight, linear track. We assume no friction in this thought experiment. Initially, the slider is prevented from moving. We observe the rod rotate around the axis. We know that centripetal force is always acting at a right angle to the tangential velocity of the center of mass of the rod. But lets say that as the rod reaches the zero angle position, we allow the slider to move in the positive y-direction with respect to an x-y coordinate system. The slider moves because of the y-component of the centrifgual reactive force acting on the axis attached to the slider. This force is equal and opposite to the centripetal force acting on the center of mass of the rod. My question is this: Because the slider and the center of mass has acquired a velocity component in the positive y-direction, is the centripetal force still at a right angle to the tangential velocity of the center of mass of the rod with respect to a laboratory frame? Or is the centripetal force "skewed" such that it causes a negative torque on the center of mass of the rod, causing the angular velocity of the rod to slow down?