Normal Forces Can Do Work

This Demonstration illustrates the fact that a normal force can do work in moving reference frames. A system consisting of a block sliding on a wedge at angle is seen in an inertial reference frame that moves to the left with speed with respect to the reference frame in which the block and the wedge are at rest. In the normal force is not perpendicular to the trajectory and thus does work. Only in the case of , when the normal force is perpendicular to the trajectory, does the work vanish.