# What is rotational potential energy?

I don't understand the concept of rotational potential energy.

During linear motion, when a force is applied, the work it does gets converted to kinetic energy and there is no change in the potential energy. Similarly, during rotational motion when a torque is applied to angularly accelerate a body, the work done by the torque leads to an increase in kinetic energy. Hence the total energy of the body also increases. This video says that the total energy of the body remains constant, hence there is a need for rotational potential energy in order to balance out the increase in the kinetic energy.

Shouldn't the total energy of the "system" including the person applying torque be conserved and the increase in kinetic energy be justified on the basis of the person's energy being decreased? Where does potential energy come into the picture?

The key to understanding the (rather poorly narrated) video is that the lecturer implies (at T=2:30) that $\Delta E=0$ from which it follows that $\Delta KE= - \Delta PE$