Question

Does the string that supports a pendulum bob do work on the bob as it swings to and fro? Does the force of gravity do any work on the bob?

Answer 1

W = F·S vector product of force and distance

Since the string is always perpendicular to the motion of the bob, the string does no work on the pendulum.

The force of gravity does have a component along the motion of the pendulum (except when the displacement is zero) and this force does work

(it is also responsible for the motion of the pendulum)