Motion, Heat and Waves
Work, Energy & Momentum
13 minStudent plan
Two conservation laws that solve problems Newton alone makes painful, and the reason a heavy slow robot hurts as much as a light fast one.
After this lesson you can
- Use conservation of energy to skip the intermediate steps
- Tell kinetic from potential energy in a real mechanism
- Work out momentum in a collision
Work and energy
Work is force multiplied by the distance moved in the direction of the force, measured in joules. Push with 10 N over 3 m and you have done 30 J of work. Push against an immovable wall and, however tired you get, you have done no mechanical work at all, because nothing moved.
Work done on a body changes its energy. Kinetic energy is ½mv², gravitational potential energy near the ground is mgh.
Energy is conserved: it moves between forms but the total does not change. A ball falling from a height converts potential to kinetic, and the drop in mgh exactly equals the rise in ½mv², which lets you find the landing speed without ever mentioning time.
In the full lesson
- Work and energy
- The v-squared problem
- Momentum
This lesson comes with the Student plan. The first module of Physics for Engineers is free.