The Wilberforce pendulum is a coupled oscillator where energy is transferred between angular oscillation and longitudinal oscillation.

With the spring at its at-rest position, twist the mass until it is wound up about one turn.  Release it and watch the angular oscillation gradually die out and the longitudinal spring and mass oscillation increase until the mass no longer rotates at all.  And then the motion slowly returns to all angular oscillation and the mass ceases to move up and down.