*Stored Energy in a stretched material*

When a material experiences a stretching forceÂ *workÂ *is done on the material by the applied force. This force causes the atoms of the material to beÂ *displacedÂ *from their original positions and so they gainÂ *internal potentialÂ (orÂ ***elastic**) energy.

It can be shown that the stored energy is given by the following equation:

Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â *STORED ENERGYÂ =Â Â½ F xÂ Â *Â Â Â

(Note:Â *F*Â must be inÂ *newtonsÂ *andÂ *x*Â inÂ *metres*Â for this equation to give energy inÂ **J**).

However,Â since F = kx, then if we substitute for F in the above equation we obtain the equation: