This text is meant to accompany class discussions. It is not everything there is to know about energy. It is meant as a prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Work from a graph of force and displacement

The space between the curve and the axis on a graph of force versus displacement represents the work done on or by the body. The size of the space is determined by calculating the area as shown above. This means a force does not have to be constant as in the formula W=Fd. Now work can vary over time and distance the amount of energy transfered trough work can be calculated.

Example

A, 202 kg, motorcycle stuntman is completing a jump. He lands on the ramp as shown. He only applies the brakes for 12 of the 20 meter landing ramp before passing out. The graph of his braking force is shown above. What is his velocity at the bottom of the ramp? (The mass is the combined mass of the stuntman and the motorcycle.)