Spring Launchers

A squeezed spring can launch an object. On a smooth, level surface all its elastic energy becomes kinetic energy:

$$\tfrac{1}{2} k x^2 = \tfrac{1}{2} m v^2$$

The spring pushes the ball until it reaches its natural length.

The object leaves the spring at its natural length, at top speed. Twice the squeeze gives twice the launch speed.

The $4\ \mathrm{J}$ in the spring becomes $4\ \mathrm{J}$ of kinetic energy.