Lesson 12 of 14
The big picture
Show on a big screen| Idea | In short |
|---|---|
| Work | W = F × s, in joules. No movement, no work |
| Two kinds | KE = ½ m v². PE = m g h. With no friction, work = energy gain |
| Energy changes form | Not created or destroyed. PE + KE stays the same |
| Friction | Mechanical energy becomes mostly heat. The total stays |
| Power | P = W ÷ t, in watts |
| A machine | Less force, more distance. Advantage = load ÷ effort |
| Three machines | Pulley, lever, ramp. The ramp sum assumes no friction |
| Nothing is free | Work out is never more than work in |
| Stored energy | A stretched or squeezed springy object stores potential energy. Held still, it has no kinetic energy. |
| Work from a graph | Work is the area under the force–displacement graph. For a steady force, the area is force × displacement. |
Energy is the capacity (ability) to do work. A machine does not reduce the work. It changes the force you use and the distance you move.
Now open Chapter 7, Work, Energy, and Simple Machines. You met most of its ideas here first.