1 Work and Power

2 What is work?  Definition: energy transferred by a _____________ to move an object a _____________ (when both the force and the motion of the object are in the same direction.)

3 Work or Not?  According to the scientific definition, what is work and what is not? a teacher lecturing to her class a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor a mouse pushing a piece of cheese with its nose across the floor

4 Work or Not?  According to the scientific definition, what is work and what is not? a teacher lecturing to her class a teacher lecturing to her class a mouse pushing a piece of cheese with its nose across the floor a mouse pushing a piece of cheese with its nose across the floor

Work or Not  Why? 5

6 What’s work?  A scientist delivers a speech to an audience of his peers.  A body builder lifts 350 pounds above his head.  A mother carries her baby from room to room.  A father pushes a baby in a carriage.  A woman carries a 20 kg grocery bag to her car?

7 What’s work?  A scientist delivers a speech to an audience of his peers. No  A body builder lifts 350 pounds above his head. Yes  A mother carries her baby from room to room. No  A father pushes a baby in a carriage. Yes  A woman carries a 20 km grocery bag to her car? No

8 Formula for work Work = _________ x Distance  The unit of work is newton x meters  One ____________ is equal to one ______  So, the unit of work is a __________  J= 1 N x m = 1 kg x m 2 /s 2

9 W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

10 W=FD Work = Force x Distance Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules (W = 20N x 10m)

11 Power  Power is the __________ at which work is done.  Power = Work * /Time or P= W/t  The unit of power is the watt.  1 watt= ______________

Work vs. Power  Work vs. Power Work vs. Power Work vs. Power 12

Concept Check  1. Describe the difference between work and power?  2. How is work being done in the following situation a. Powerlifting b. Dropping your textbook c. Doing a handstand  What is the unit for lightbulbs? Why is that unit used? 13

Math Practice  1. A crane use an average force of 5300 N to lift a girder 25 m. How much work does the crane do on the girder?  2. Aylssa powerlifts Kyle over her head 1 m with a force of 250 N. How much work was done?  3. While rowing in a race, John uses his arms to exert a force of 165 N per stroke while pulling the oar m. How much work does he do in 30 strokes? 14

Math Practice  4. While rowing in a race, John does 3960 J of work on the oars in 60.0 s. What is his output in watts.  5. Steve using a jack does 4320 J of work to lift a car 1.5 m in s. What is the power output?  6. Mr. Farrell walks up the stairs on his way to make copies. He weight 622 Newtons and the stairs go 5.75 vertically. a. Calculate my output if I climb the stairs in 8.9s. b. What is I climb the stairs in 7.2 s? 15