What is work ? The product of the force applied to an object and the distance through which that force is applied.

Is work being done or not? Mowing the lawn Weight-lifting Moving furniture up a flight of stairs Pushing against a locked door Swinging a golf club YES NO

Calculating Work All or part of the force must act in the direction of the movement. work = force x distance

Do you do more work when you finish a job quickly? Work does NOT involve time, only force and distance. No work is done when you stand in place holding an object. Labeling work: w = F x d Newton X meter (N m)

The Joule 1 newton-meter is a quantity known as a joule (J). Named after British physicist James Prescott Joule.

How quickly work is done. Amount of work done per unit time. Power How quickly work is done. Amount of work done per unit time. If two people mow two lawns of equal size and one does the job in half the time, who did more work? Same work. Different power exerted. POWER = WORK / TIME

The watt A unit named after Scottish inventor James Watt. Invented the steam engine. P = W/t Joules/second 1 watt = 1 J/s

Watts Used to measure power of light bulbs and small appliances An electric bill is measured in kW/hrs. 1 kilowatt = 1000 W

Practice #1 Jenny pulls on a large box with a horizontal force of 50 N. The boxes are too heavy and do not move. Calculate the amount of work done by Jenny.

Practice #2 Jenny then pulls on the same large box with a horizontal force of 70 N. The box moves a mere 5 cm. Calculate the amount of work done by Jenny.

Practice #3a In the World’s Strongest Man competition, a man lifted up a 140 kg boulder by 1 m. Calculate the work done by the man. Note: Find the object’s weight to find the amount of force.

Practice #3b In the World’s Strongest Man competition, a man lifted up a 140 kg boulder by 1 m. If it took the man 6 seconds to lift the boulder up, how much power did he have?

Practice #4 Student A pushes a box across the floor with a force of 30 N. Student B pushes a similar box across the floor with a force of 50 N. If both boxes traveled the same distance of 5 meters in 3 seconds, which Student had more power?