1. Chapter 5 – Work, Power, & Machines “Give me a lever and a place to stand and I will move the earth.” Archimedes

2. WORK Work: Transfer of Energy that occurs when a force makes an object move. NOT every force results in work –The direction of the force and the motion of the object must be taken into account 2 conditions for work to happen –Object must move –Force and movement are in the same direction W = F × d Work (J) = Force (N) × Displacement (m) × cosө F = ma

3. Examples of work –a soccer player kicking a goal –a pitcher throwing in the first pitch –a student lifting a backpack full of books upon her shoulder –a father picking up a child off the floor –a track star launching the shot-put The force exerted on the object and its motion are in the same direction.

4. Is this really work? Draw force vector & motion vector to verify answer. A body builder lifts 350 pounds above his head. A mother carries her baby from room to room. Busy mom pushes a grocery cart. A woman carries a 20 kg grocery bag to her car? Yes No Yes No

5. Work Example Problem A crate is moved across a frictionless floor by a rope. The tension in the rope is 50 N. How much work is done in moving the crate 10 m?

6. Power Power: the rate at which work is done. P = W/TSI unit: Watt (W) Power (W) = Work (J) Time (sec) work and power

7. Example Problem: Work & Power 2 soccer players work out in the off season by sprinting up a 100-m hill before stopping, resting, and walking back down. Mia and Julia weigh the same, 588N. It takes Mia 42 sec and Julie 38 sec to reach the top of the hill. A.Which athlete did more work? B.Which athlete produced more power?

8. Bill Nye – Simple Machines http://www.youtube.com/watch?v=9T7tGo sXM58&feature=relmfuhttp://www.youtube.com/watch?v=9T7tGo sXM58&feature=relmfu