1. Power

2. Power  Power (P) – rate at which work is done. Also, rate at which energy is transformed.Also, rate at which energy is transformed.  P =  SI Units: Worktime Js kg*m 2 /s 2 s = kg*m 2 /s 3 = Watts (W) =

3. Be Careful!  Be careful not to confuse Work with Watts. The Difference:The Difference:  Work is a quantity. W = FdW = Fd  Watts are units. P = 100 WP = 100 W

4. Power  Power =  Power = Force x velocity P = FvP = Fv  Assuming F and v are in the same dimension. Force x distance timedistancetime

5. Power  John does 400 J of work in 10 seconds. How much power does John develop? P = W/tP = W/t P = (400 J)/(10 s)P = (400 J)/(10 s) P = 40 WattsP = 40 Watts

6. Power  If the power needed to operate a 100.-Watt light bulb is redirected to lift a 1.00-kg crate at constant speed, how far is the crate lifted in 60.0 seconds? P = W/tP = W/t P = Fd/tP = Fd/t P = mgd/tP = mgd/t (100. W) = (1.00 kg)(9.81 m/s 2 )d / (60.0 s)(100. W) = (1.00 kg)(9.81 m/s 2 )d / (60.0 s) (100. W) = (9.81 N)d / (60.0 s)(100. W) = (9.81 N)d / (60.0 s) (6.00x10 3 J = (9.81 N)d(6.00x10 3 J = (9.81 N)d d = 612 m (!!!)d = 612 m (!!!)

7. Power  An elevator weighing 1000. N rises vertically at a constant 2.00 m/s. What power does the elevator develop? (Neglect friction). P = W/tP = W/t P = Fd/tP = Fd/t P = FvP = Fv P = (1000. N)(2.00 m/s)P = (1000. N)(2.00 m/s) P = 2.00x10 3 W = 2.00 kWP = 2.00x10 3 W = 2.00 kW

8. What Do You Pay For?  The “power” company doesn’t charge you for power... They charge you for energy.They charge you for energy.  Measured in kilowatt-hours. 1 kWh = energy changed (work done) by a 1000- W power source for one hour.1 kWh = energy changed (work done) by a 1000- W power source for one hour. 1 kWh = 1000 W x 3600 s = 3,600,000 J1 kWh = 1000 W x 3600 s = 3,600,000 J  It costs as much to run a 1000-W heater for an hour as it does to run a 100-W light bulb for 10 hours.

9. By the, I have the power! W Greyskull t

10. By your F combined v, I am Captain Planet!

11. W mighty t morphin Rangers