Work, Power and Energy; Wind and Water Power
How forces transfer energy, how fast that transfer happens, and how a mountain river is turned into electricity
Big Idea: Whenever a force moves a body along its line of action it does work, and work is exactly the amount of energy transferred. Energy can be stored as motion (kinetic) or as position in a field (potential), and in a system free of friction the total mechanical energy stays constant. Power tells us how quickly energy is delivered. These few ideas run everything from a lifted schoolbag to the Toktogul hydroelectric station on the Naryn river.
By the end you will be able to:
- compute mechanical work W = Fs cos α and read the sign of the work,
- use power P = W/t = Fv and its unit, the watt,
- apply kinetic energy Ek = mv2/2 and potential energy Ep = mgh,
- use the conservation of mechanical energy to solve problems without knowing the forces in detail,
- calculate the efficiency η of a real machine, and explain how wind and water carry usable energy.