1. Chapter 9.2 Power

2. Power vs. Work When carrying a load up some stairs, you do the same amount of work whether you walk or run up the stairs. Whether you walk 3 km or run 3 km, you do the same amount of work (your weight x distance), burn roughly the same amount of calories, and use the same amount of energy. So what is power?

3. Power equals the amount of work done divided by the time interval during which the work is done. 9.2 Power

4. Power is the rate at which work is done. 9.2 Power The unit of power is the joule per second, also known as the watt. One watt (W) of power is expended when one joule of work is done in one second. One kilowatt (kW) equals 1000 watts. One megawatt (MW) equals one million watts. P = w/t

5. Power 100 W incandescent light bulb How much electrical energy per second? 100 joules per second.

6. Jet engine vs. lawn mower engine Both receive ½ gallon of fuel (same energy, same work) A high-power jet engine does work rapidly, uses ½ gallon in 1 second. The low-powered lawn mower engine does work slowly, using ½ gallon in 30 minutes. 9.2 Power vs.

7. Power When you run 3 km rather than walk, you use the energy more quickly because your body demands more energy per unit time. When you compare the amount of energy required to operate an electric dryer vs. a laptop computer, the electric dryer demands more energy per unit time. More energy per unit time means more power is required! Needs 5500 J/s Needs 50 J/s