2. Chapter 10 Energy, Work and Simple Machines

3. Energy The ability to produce change in itself or its’ environment.

4. Energy of Motion: Kinetic Energy

5. Newton's 2 nd Law F = ma Equation for an object in motion. v 1 2 = v 2 2 + 2ad F m = a

6. Kinetic Energy v 1 2 = v 0 2 + 2Fd m v 1 2 - v 0 2 = 2Fd m ½m(v 1 2 - v 0 2 ) = Fd

7. Kinetic Energy Fd = Work ∆K = Work

8. Kinetic Energy ½mv 1 2 - ½m v 0 2 = Fd K = ½mv 2 ΔK = Fd

9. Work Applying a Force through a distance is WORK!! Fd = Work ΔK = Work

10. Work Work is measured in Joules(J). J = Nm J = kg m 2 s 2

11. Example 1 A 105g hockey puck is sliding across the ice. A player exerts a 4.5N force over a distance of 0.15m. How much work does the player do on the puck? What is the change in the pucks energy?

12. Example 1

13. Given: m=105g=0.105kg F=4.5N d=.15m Eq:W=F d W=(4.5N)x(0.15m) W=0.68J

14. Example 2 A gardener pushes a lawn mower across a 20m lawn. He applies a 250N force to the handle. If the handle makes a 30º with the ground, how much work is done to make one pass across the lawn?

15. Example 2 30º F d

16. Example 2 x comp:F x = Fcos30º Given:d=20m F=250N at 30º F x = 250cos30º F x = 217N Eq:W = F x d W = 217N X 20m W = 4340J

17. Homework 10-1 Practice Problems: 1-5 Page: 227 Practice Problems: 6-8 Page: 229 Due: 1/27/03

18. Power – watts - W Power is the rate at which work is done. Power = work time

19. Power P = W t P = Fd t

20. Example 2 A farmer lifts a 1.0kg bail of hay 2m. On a good day it takes the farmer 0.5s. How much power does the farmer produce.

21. Example 2 Given:d = 2m m =1kg t = 0.5s Eq:P = W t P = mgd t P = Fd t

22. P = (1kg)(9.8m/s2)(2m) 0.5s P = 39.2 W P = mgd t

23. Homework Problems: 25,26,29 & 30 Page: 242 Due: 2/1/07

24. Machines A machine eases the load by changing either the magnitude or the direction of a force as it transmits energy to the task.

25. Mechanical Advantage FrFr FeFe

26. Effort Force ( Fe ) : The force you apply to the machine. Resistance Force ( Fr ) : The force exerted by the machine.

27. Mechanical Advantage Mechanical Advantage (MA) The number of times the machine multiplies the effort force. MA = resistance force effort force MA = Fr Fe

28. Ideal Mechanical Advantage drdr de Fr Fe

29. Ideal Mechanical Advantage Work In = Work Out IMA = d e d r

30. The Lever Fr Fe lr le

31. MA lever = effort arm length resistance arm length MA lever = l e l r

32. Pulleys Fixed Pulley Movable Pulley

33. Mechanical Advantage of a Pulley: The number of ropes supporting the resistance weight. MA = 1MA = 2MA = 3

34. Block and Tackle The arrangement of several pulleys.

35. Wheel and Axle rwrw rara MA = radius of wheel radius of axle MA = r w r a

36. Inclined Plane A slanted surface used to raise objects l h MA = l h

37. Efficiency Efficiency = Work Out x 100% Work In Efficiency = F r x d r x 100% F e x d e

38. Compound Machine MA = MA 1 x MA 2 1 2

39. Homework 10-3 Practice Problems: 13-16 Page: 238 Section Review: 1-4 Page: 238 Due: 1/30/03

40. Homework 10-4 Problems: 31,33,37, 40, and 41 Pages: 242-245 Due: 1/31/03 Test: 2/4/03

41. Homework 10-5 Problems: 48, 49, 50, 52, and 53 Pages: 242-245 Due: 2/3/03 Test: 2/4/03