a. If the friction force is zero, then energy transforms between these two forms. The system is conservative and no energy is lost in the transformation. b. If friction is present, then mechanical energy is lost to friction at the pivot, and to air resistance. The kinetic energy and the potential energy gradually decrease, so the pendulum’s energy will run down. Real grandfather clocks are subject to friction, so they must be periodically “wound up”.
Work Step by Step
At the 2 endpoints of the pendulum’s swing, its energy is all in the form of gravitational potential energy. At the bottommost point of its swing, all of its energy is kinetic energy.