advertisement

POWER What is the work done in climbing a flight of stairs of height h? W=F•d d What is the work done in climbing a flight of stairs of height h? W=F•d POWER Power = Work / Time POWER IS: Do you get more tired when you run or when you walk up the stairs? • the rate at which work is done • how fast work is done • how much work you can do per second What is the difference? h TIME POWER POWER Metric system units for Power are: Electric Power = Current × Voltage Watts (W) What are the units for Power? 1 Watt = 1 Joule per second 1 W = 1 J/s 1 POWER Other units for Power: W Electrical Power is sold in kilowatt/hours (kWh): P 1 kW = 3,600,000 J/hr t Cars and Machines are rated in Horsepower (hp) 1 hp = 746 W (a very strong horse! ) MEASURED IN JOULES (J) MEASURED IN WATTS (W) MEASURED IN SECONDS (s) 1 W = 1 J/s Electric Power = Current × Voltage POWER What is the work done in climbing a flight of stairs of height h? W=F•d Watt Demonstration: Lift a 1-N mass a distance of 1 meter, and you have done 1 Joule of Work. Do this once each second, and your power output is 1 Watt. What is the work done in climbing a flight of stairs of height h? W=F•d d POWER Power = Work / Time POWER IS: Do you get more tired when you run or when you walk up the stairs? • the rate at which work is done • how fast work is being done • how much work you can do per second What is the difference? h TIME 2 Example: • next… What is the power output of a 100 N person who runs up a 10 m high flight of stairs in 2.5 s? W = Fd = (100 N)x(10 m) = 10,000 J P=W/t = (10,000 J) / (2.5 s) h = 4000 W Power, Energy, Work … all together now. THE RATE OF DOING WORK OR CONVERTING ENERGY. Power = Work / Time Power = Energy / Time UNIT- WATT = JOULE PER SECOND 3