Normal Forces Can Do Work

angle α in degrees

35

u

time

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

α

is seen in an inertial reference frame

S'

that moves to the left with speed

u

with respect to the reference frame

S

in which the block and the wedge are at rest. In

S'

the normal force is not perpendicular to the trajectory and thus does work. Only in the case of

u=0

, when the normal force is perpendicular to the trajectory, does the work vanish.