What is WORK? A – The Meaning of Work 1 – Work – is done on an object when the object moves in the SAME direction in which the force is exerted. Example: Pushing a child on a swing, pulling books out of your backpack 2 – No motion = NO WORK a) If the object does not move, there is no work being done even if you exert a force! Example: Pushing a car that is stuck in the snow

More Examples: 1 – lifting your backpack up = WORK: why? The motion of the backpack was the SAME direction as the force on it. 2 – Carrying your backpack to school = NO WORK:why? Carrying your backpack moves it horizontally, and the force to hold it is vertical, so the force and movement are in DIFFERENT directions 3 – Rolling a suitcase = partial work: why? The only work is the horizontal pull that results in the movement of the suitcase. The vertical pull holds it up, but that is not part of the work.

Calculating WORK? A – The amount of work you do depends on the amount of force exerted and the distance the object moves. WORK = Force x Distance Joules = Newtons x meters B – The SI unit for work is called the JOULE one joule = work done to move 1 Newton a distance of 1 meter Work Forcedistance

1.A boulder weighing 5.8 Newtons is lifted 2 meters. How much work is done? W = 5.8 x 2 W = 11.6 Joules 2. A force of 6 Newtons is used to push a couch along the floor a distance of 8.2 meters. How much work was done? W = 6 x 8.2 W = 49.2 Joules Calculating Work Examples WORK = Force x Distance

3. At a tournament, a group of men exerted 8,000 Newtons on a monster truck for 6 meters. How much work was done? W = 8000 X 6 W = 48,000 Joules 4. A construction worker did 96 Joules of work moving a steel beam 6.4 meters across a construction site. How much force did the construction worker use to move the steel beam? = 15 Newtons 5. A man did 48 Joules of work lifting his big screen television. If he used a force of 8 N to lift the television, how high did he have to lift it? 48 8 = 6 meters

Power A – Power – is the rate at which work is being done. It equals the amount of work done in a unit of time. In other words: You do the same amount of work in less time, or you can do more work in the same amount of time. For example: It takes the same amount of work to push a desk slowly or quickly across a floor. However, the faster you move the more power is applied. B – The SI unit for power is Joules/second or the Watt 1 watt = 1 J/s 1 Kilowatt = 1000 watts FYI – 1 horsepower = 746 watts

Power = Work or Power = Force x Distance Time Time Calculating Power 1)A machine produces 4000 Joules of work in 5 seconds. How much power does the machine produce? 2)A box that weighs 1000 Newtons is lifted a distance of 20 meters in 10 seconds. How many kilowatts of power are produced? 3) At a tractor pull, one machine has a run that produces 28,000 Joules in 2 seconds. How many Watts of power did this tractor produce?