Physics
Elastic Potential Energy
Quick fact
A typical slingshot stores about 20 joules of elastic potential energy when fully drawn—enough to lift a 2 kg weight one meter off the ground.
Why this is interesting
Why can a stretched rubber band launch a paper plane across the room, and a compressed spring power a toy car? The answer lies in a hidden form of energy waiting to be released.
Read the full explanation
Understanding Elastic Potential Energy
Imagine you have a spring attached to a wall. If you pull the spring outward, you're doing work against the spring's natural tendency to snap back. That work doesn't vanish—it gets stored as elastic potential energy inside the spring. The farther you stretch it, the more energy you store. When you let go, that stored energy converts into kinetic energy, sending the spring flying back toward its original shape. The same principle applies to a compressed spring: pushing it in stores energy, and releasing it unleashes that energy. Think of it as a 'mechanical battery' that stores energy by changing shape.
A deeper explanation
The amount of elastic potential energy (U) stored in an ideal spring is given by U = ½ k x², where k is the spring constant (stiffness) and x is the displacement from equilibrium. This relationship follows from Hooke's law, which states that the restoring force is proportional to displacement (F = -kx). The work done to stretch or compress the spring is the area under the force-displacement curve, which is a triangle, hence the ½ factor. Elastic potential energy is important because it allows mechanical energy to be temporarily stored, then efficiently converted to kinetic energy—enabling everything from car suspensions to pogo sticks. It also illustrates the conservation of mechanical energy in ideal systems without friction.