Stretching energyThe stretching part of the energy is easiest to understand. First, think about a spring -- it takes effort to stretch or compress a spring from its normal length. We call the normal length the natural or equilibrium length of the spring. This is the length the spring has when no force is applied. Consider the model of a spring below:
Use the mouse to drag the block on the end of the spring. The force used to move the block is shown on the left graph (marked F) and the stored energy (marked E) is shown on the right.
Things to notice