Work Power Simple Machines What is WORK o

Work, Power & Simple Machines

What is “WORK? ” o Work is defined as A force acting through a distance o In order for “work” to be done n n n There must be a force (push, pull, lift, throw…) There must be movement over some distance The motion must be in the same direction as the force applied

Kinetic Energy o The energy of motion

Work or Not Work Example Pushing a box across the floor A waiter carrying a tray of food to a table Pushing down on the pedal of a go cart Pushing on a locked door Direction of Force Direction of Motion Doing work? Yes

Work or Not Work, Continued Example Pulling a suitcase on wheels through the airport Pushing a car down an incline Writing an essay in cursive Writing an essay on the computer Direction of Force Direction of Motion Doing work?

Is work done? o Your friend pushes his book to you by sliding it across the desk o You lift the book off of the desk o You hold the book in your hands o You pass the book to another classmate o You walk the book to another classmate

Measuring Work o Work is determined by considering Force and Distance o Work is equal to the amount of force applied times the distance the object moves Work = force (newton) x distance (meter) W = F x D The unit for Work is the “newton-meter (N-m)” or the “joule(J)” o If a force of 1 newton is applied to move an object 1 meter, then 1 newton-meter, or 1 Joule of work is done

In this diagram the same amount of work is done using two different methods: A small force over a large distance A large force over a small distance

Solving work problems o If I push an object with a force of 50 Newton's, and it moves two meters as a result of that push, how much work is done? W=Fx. D W = 50 N x 2 m W = 100 N-m or 100 J

Copy and complete…. . o If I lift an object 0. 5 meters and the object has a weight of 150 N, how much work is done? o If I carry the same object across the room 5 meters, how much work is done?

What is “Power? ” o Power tells the rate, or “how fast, ” work is being done; o Power measures work in relation to time; o Power is equal to the amount of work divided by the amount of time over which the work is done

Calculating Power = work/time P = w / t P = (force x distance) / time The unit for work is the Joule The unit for time is the second The unit for Power is joules/sec (J/s) or the Watt (W) 1 Watt of power means that 1 joule of work is being done in 1 second

P=w/t o If more work is done in the same amount of time, what happens to the Power? n It increases o If the same amount of work is done in less time, what happens to Power? n It increases

Common Power Terms o A 75 watt light bulb does 75 Joules of work in 1 second; it takes 75 watts of power to make the light bulb glow o A kilowatt is 1000 watts o How many Kilowatts of power are used by a 1200 Watt hair dryer?

Solving Power Problems o How much power is used when a person does 500 Joules of work in 20 seconds? P=w/t P = 500 / 20 P = 25 Joules/sec or 25 Watts

Solving Power Problems o A person weighing 600 N gets on an elevator. The elevator lifts the person 6 m in 10 seconds. How much power was used to lift the person? P=w/t P = (f x d) / t P = (600 x 6) / 10 P = 3600 / 10 P = 360 J/s or 360 Watts