Elastic potential energy is the energy stored in an object when it is stretched or squeezed out of its original shape.

When you pull a spring, it tries to snap back to its normal size. This "pulling back" force exists because the spring has stored energy. This stored energy is called potential energy. It is specifically called "elastic" because it comes from the material's ability to return to its original form.

How a Spring Stores Energy

Every spring has a property called the spring constant, often written as 'k'. This number tells you how stiff a spring is. A high 'k' value means the spring is very hard to stretch. A low 'k' value means the spring is soft and easy to pull. When you apply a force to change the length of the spring, you are doing work on it. This work does not disappear; it stays inside the spring as elastic potential energy.

The Formula for Elastic Potential Energy

Physics uses a simple formula to calculate how much energy a spring holds:

U = ½ kx²

• U is the elastic potential energy measured in Joules.
• k is the spring constant.
• x is the distance the spring has been stretched or compressed from its natural length.

The 'x' is squared, which means if you stretch a spring twice as far, it stores four times as much energy.

Real-World Examples

You encounter elastic potential energy in many everyday items:

• Trampolines: When you jump on a trampoline, the springs stretch. They store energy from your landing and then release it to push you back into the air.
• Mechanical Watches: A small coiled spring inside a watch stores energy as you wind it. It slowly releases this energy to move the clock hands.
• Archery: Pulling back a bowstring stretches the bow limbs. The energy stored in the bowed shape is what launches the arrow forward.