12.1 Work I can: -recognize force and displacement must be in the same direction for work to be done. -use the equation w=f x d to calculate work

Why do we say we are going to work? To use, work means exerting force with your muscles. In science, it takes a different meaning!

What is work? How do you lift your car when you want to change a tire? Work: transfer of energy to a body by the application of a force that causes the body to move in the direction of the force. –Work=force x distance –Examples in the weight room… What unit should be used? –1N x m =1J= 1kg x m/s 2 –How much work are you doing to eat an apple?

Press your hand against the surface of your desk at hard as you can. Have you done any work? The answer is no, no matter how tired your effort makes you feel. It must move. Walking across the room while holding an object- is NOT work! –Movement is not in the same direction as force, so arms do no work When work is done: energy is transferred from one object to another

Which is doing more work?

Practice Father is lifting daughter repeatedly in the air. How much work does he do with each lift? Assume he lifts her 2m and exerts an average force of 190 N. –Step 1: given is F=190N, distance d=2m. Unknown= W –Step 2: W= 190N x 2m= –Answer: 380 J Turn to page 379 and complete 1-5.

What is Power? Does running up a flight of stairs require more work than walking up slowly? Power: quantity that measures the rate at which work is done or energy is transformed. –Power= work/time –Does running v. walking affect power? Power is measured in watts (W) –1 W= amount of power required to do 1J of work in 1 s.

Practice It takes 100 kJ of work to lift an elevator 18m. If this is done in 20 s, what is the average power of the elevator during the process? –Step 1: given W=100kJ, kJ= 1 x 10 5 J, time=20s, distance=18 m –Step 2: P=100,000J/20s= –Answer: 5000 W or 5kW Complete pg

Machines and Mechanical Advantage Machines multiply and redirect forces Mechanical Advantage: measures how much a machine multiples force or distance. –It’s a force, so measured in N. Mech. Advantage=output force/input force= input distance/output distance.

Practice Complete pg