# How does energy change with a swinging pendulum?

At maximum height, the pendulum has maximum potential energy ${E}_{p} = m g h$ and zero kinetic energy.
As it falls it loses vertical height and so loses potential energy, but gains an equivalent amount of kinetic energy ${E}_{k} = \frac{1}{2} m {v}^{2}$ by virtue of building up speed.
At all times, the Principle of Conservation of Mechanical Energy applies in that the sum of ${E}_{P} + {E}_{k}$ is always constant at all times during the pendulum motion.