1. Work and Power

2. What does work mean to you?

3. In physics, work has a very specific meaning. It is the action to make things change Work= force x distance W=F x d Unit: N-m : Joule Work

4. W = F x d Therefore: You must have MOTION in order to have work… something has to change position

5. Work = Force x distance

6. Work …the motion has to take place parallel to the direction of the force

7. Garcon does work when he picks up the tray but not while he carries it around the room Garcon is not doing work Work and Energy…the motion (distance) is parallel to the direction of the force

8. Is Atlas doing work? NO Atlas is staying in place Atlas is not doing work

9. Is work being done on the wall? work may be done on the prisoner’s muscles …stretching, squeezing them, pumping the blood through the veins.. but this is not work being done on the wall be clear where the work goes

10. Is work being done?

11. Example Problems How much work is done by a toy car with an applied force of 12 N which is moved for 39 m?

12. Power

13. Pit Pony

14. A little bit of history To find out how the power of his engine compared to that of a horse, James Watt measured how fast an average horse could do work. He found the answer and expressed the amount of work performed per second as a horsepower. 1 horsepower = 746 Watts A horse exerting 1 horsepower can raise 330 pounds of coal 100 feet in a minute. In the US we rate engines in terms of horsepower (hP) and electricity in watts (kilowatts, megawatts)

15. Horsepower

16. Power Power – the rate at which work is done. Power = Work/time Unit is Watt (joule/second)

17. ONE OF 2 THINGS POWER = WORK DONE TIME 2X WORK OR WORK TIME ½ TIME What can a more powerful engine do?

18. Example Problems If a 450 N boulder is dropped 2.4 m in 25 seconds, how much power is exerted on the object?

19. The weight lifter used a force of 980 N to raise the barbell over her head in 5.21 seconds. Approximately how much work did she do in raising the barbell?

20. A mechanic used a hydraulic lift to raise a 12,054 N car 1.89 m above the floor of a garage. It took 4.75 s to raise the car. What was the power output of the lift? Example Problems