1. WORK, POWER, AND MACHINES 9.1

2. WORK  A quantity that measures the effects of a force acting over a distance  Work = force x distance  W = Fd

3. WORK  Work is measured in: NmNm  Joules (J)

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

5. WORK EXAMPLE  Work = Fd  Work = (5200 N)(25m)  Work = 130000 N  m = 130000 J

6. POWER  A quantity that measures the rate at which work is done  Power = work/time  P = W/t

7. POWER  Watts (W) is the SI unit for power  1 W = 1 J/s

8. POWER EXAMPLE  While rowing in a race, John uses 19.8 N to travel 200.0 meters in 60.0 s. What is his power output in Watts?

9. POWER EXAMPLE  Work = Fd  Work = 19.8 N x 200.0 m= 3960 J  Power = W/t  Power = 3960 J/60.0 s  Power = 66.0 W

10. MACHINES  Help us do work by redistributing the force that we put into them  They do not change the amount of work

11. MACHINES  Change the direction of an input force (ex car jack)

12. MACHINES  Increase an output force by changing the distance over which the force is applied (ex ramp)  Multiplying forces

13. MECHANICAL ADVANTAGE  A quantity that measures how much a machine multiples force or distance.

14. MECHANICAL ADVANTAGE Output Force Input Force Input distance Output Distance Mech. Adv = Mech. Adv. =

15. MECH. ADV. EXAMPLE  Calculate the mechanical advantage of a ramp that is 6.0 m long and 1.5 m high.

16. MECH. ADV. EXAMPLE  Input = 6.0 m  Output = 1.5 m  Mech. Adv.=6.0m/1.5m  Mech. Adv. = 4.0

17. ENERGY 9.3-9.4

18. ENERGY AND WORK  Energy is the ability to do work  whenever work is done, energy is transformed or transferred to another system.

20. ENERGY  Energy is measured in:  Joules (J)  Energy can only be observed when work is being done on an object

21. POTENTIAL ENERGY PE  the stored energy resulting from the relative positions of objects in a system

22. POTENTIALENERGY PE POTENTIAL ENERGY PE  PE of any stretched elastic material is called Elastic PE  ex. a rubber band, bungee cord, clock spring

25. GRAVITATIONAL PE  energy that could potentially do work on an object due to the forces of gravity.

26. GRAVITATIONAL PE  depends both on the mass of the object and the distance between them (height)

27. GRAVITATIONAL PE EQUATION grav. PE= mass x gravity x height PE = mgh or PE = wh

28. PE EXAMPLE  A 65 kg rock climber ascends a cliff. What is the climber’s gravitational PE at a point 35 m above the base of the cliff?

29. PE EXAMPLE  PE = mgh  PE=(65kg)(9.8m/s 2 )(35m)  PE = 2.2 x 10 4 J  PE = 22000 J

30. KINETIC ENERGY  the energy of a moving object due to its motion.  depends on an objects mass and speed.

31. KINETIC ENERGY  What influences energy more: speed or mass? ex. Car crashes  Speed does

32. KINETIC ENERGY EQUATION KE=1/2 x mass x speed squared KE = ½ mv 2

33. KE EXAMPLE  What is the kinetic energy of a 44 kg cheetah running at 31 m/s?

34. KE EXAMPLE  KE = ½ mv 2  KE= ½(44kg)(31m/s) 2  KE=2.1 x 10 4 J  KE = 21000 J

36. MECHANICAL ENERGY  the sum of the KE and the PE of large-scale objects in a system  work being done

37. NONMECHANICAL ENERGY  Energy that lies at the level of atoms and does not affect motion on a large scale.

38. ATOMS  Atoms have KE, because they are constantly in motion.  KE  particles heat up  KE  particles cool down

39. CHEMICAL REACTIONS  during reactions stored energy (called chemical energy)is released  So PE is converted to KE

40. OTHER FORMS  nuclear fusion  nuclear fission  Electricity  Light

41. ENERGY TRANSFORMATIONS 9.4

43. CONSERVATION OF ENERGY  Energy is neither created nor destroyed  Energy is transferred

44. ENERGY TRANSFORMATION  PE becomes KE  car going down a hill on a roller coaster

45. ENERGY TRANSFORMATION  KE can become PE  car going up a hill KE starts converting to PE

47. PHYSICS OF ROLLER COASTERS  http://www.funderstanding.com/k12/coaster/ http://www.funderstanding.com/k12/coaster/