Energy

1. Work and Power Simple Machines Kinetic Energy Potential Energy Energy

2. Equations used so far . . . (vf-vi) (y2-y1) a t slope F d m v a t W (x2-x1) g m

3. Work and Power

4. Work • Occurs when a force causes something to move a distance • Motion must be in the same direction as the force

5. Is this an example of work? force distance yes

6. Is this work? force Yes…if he LIFTS the barbell distance

7. Is this work? distance? force No…why not?

8. Is this work? force No…why not? distance

9. Work Equation W F d Work = Force x Distance W = Fd

10. Units for Work W = Fd Or Nm Joules (J)

11. Practice Problem John uses 45 Newtons of force to push his lazy dog 3.2 meters across the kitchen floor. How much work does John do? F = 45 N d = 3.2 m W = ? W = Fd W = (45 N)(3.2 m) W = 144 J s.f.: 140 J

12. Power W P t • The rate at which work is done • In other words…how fast work is done Power = Work time P = W t Units Joules second = Watts (W)

13. Practice Problem If John takes 5.0 seconds to push his dog, what is his power output? W = 144 J t = 5.0 s P = ? P = W/t P = 144 J/5.0 s P = 28.8 W s.f.: 29 W

14. A crane uses an average force of 5200 N to lift a girder 25 m. How much work does the crane do?

15. An apple weighing 1 N falls a distance of 1 m. How much work is done on the apple by the force of gravity?

16. A bicycle's brakes apply 125 N of friction force to the wheels as the bike moves 14.0 m. How much work do the brakes do?

17. A mechanic uses a hydraulic lift to raise a 1200 kg car 0.50 m off the ground. How much work does the lift do on the car?

18. While rowing across the lake during a race, John does 3960 J of work on the oars in 60.0 s. What is his power output in watts?

19. Anna walks up the stairs on her way to class. She weighs 565 N, and the stairs go up 3.25 m vertically. • A. What is her power output if she climbs the stairs in 12.6 s? • B. What is her power output if she climbs the stairs in 10.5 s?

20. Practice Problems: p. 432 #1-4 1. 130000 J 2. 1 J 3. 1750 J 4. 5900 J p. 434 # 1-2 1.66 W 2a. 146 W 2b. 175 W Assignment: W W P F t d

21. Review What does the term “work” mean in your everyday life? What does the term “work” mean in Physical Science? • Work is the ability to produce a force that causes movement.

22. Work and Power Practice Problems: Mixed Equations (Front only) • W = 237825 J • d = 0.6 m • F = 27 N • a) P = 494 watts • b) d = 3 m • W = 300 000 J

23. Mixed Practice (complete the back) W W (vf-vi) (y2-y1) P a F t d t slope F d Velocity Work Force m v t a Acceleration W (x2-x1) g m Slope Weight Power

24. Review • What does the term “power” mean in Physical Science? • Power is the rate (how fast) an individual is able to do work. • What are the two main families of simple machines? • 1. Lever Family • 2. Inclined Plane Family

25. Household tools Mini-Lab

26. Household Tools Mini-LabPurpose: To relate household tools to the six simple machines. Simple Machines Reading Guide 13.2

27. The 6 Simple Machines

28. Lever Family Inclined Plane Family The 6 Simple Machines

29. The Lever Family • Lever • Pulley • Wheel & Axle

30. Lever Family 1. Lever

31. *Levers-First Class • In a first class lever the fulcrum is in the middle and the resistance and effort is on either side • Think of a *see-saw

32. *Levers-Second Class • In a second class lever the fulcrum is at the end, with the resistance in the middle • Think of a *wheelbarrow

33. Levers-*Third Class • In a third class lever the fulcrum is again at the end, but the effort is in the middle • Think of a pair of *tweezers

34. 1st Class 2nd Class 3rd Class Fulcrum (F) Resistance (R) Effort (E) What's In The Middle?

35. Levers • Levers make work easier by reducing the amount of force necessary to move a load. • Mechanical Advantage of a lever is equal to effort arm divided by the resistance arm. • MA = effort resistance

36. Lever Family 2. Pulley

37. Pulleys • The pulley distributes the force of the load among several ropes in the system • Using a single pulley does not multiply the input force, but it does change the direction of the input force. • Using several pulleys increases the distance the of the input force causing a larger output force. The mechanical advantage is equal to the number of ropes sharing the load. • MA = # of ropes-1 or MA = # of pulleys • Figure 3 pg 440

38. Lever Family 3. Wheel and axle

39. Wheel and Axle • A wheel and axle system makes work easier by increasing a small amount input force applied to the wheel. • Mechanical Advantage is the wheel radius divided by the axle radius. • MA = radius wheel radius axle

40. The Inclined Plane Family • Inclined plane • Wedge • Screw

41. Inclined Plane Family 4. Inclined Plane

42. Inclined Plane • An inclined plane makes work easier by increasing the distance over which force is applied. Less input force is required to lift a load. • Mechanical Advantage of an inclined plane is equal to the distance of the sloped edge divided by the height. • MA = slope height

43. Inclined Plane Family 5. Wedge

44. Wedge • A wedge is two inclined planes put back to back. • Mechanical Advantage of a wedge is the slope length divided by the width of the wedge. • MA = slope width

45. 6. Screw

46. Screw • A screw is an inclined plane wrapped around a cylinder. • Mechanical Advantage of a screw is length of the treads divided by the diameter of the cylinder. • MA = length diameter

47. MA = F out F in Mechanical Advantage = load effort

48. Work & Machines

49. How do machines make work easier? • By changing the size or direction of the FORCE • Machines DO NOT make work less • Force is less, therefore distance is greater W = F d

50. Example: Lever Less force Greater distance