If the motion of a pendulum or a mass on a spring can be called simple harmonic motion if no energy is lost as time goes by.

It is interesting to graph the potential energy (stored in the spring, for the mass on the spring) and kinetic energy as a function of time as well as a function of position. See if you can predict the shape of the graphs when they are drawn as a function of position before you look at them.

When you look at the graphs of the energy as a function of time, consider this: how many cycle does the energy go through for each complete cycle of the mass on the spring?

Here's a simulation of a pendulum, showing bar graphs for the energy.