2. Work and Energy

3. ENERGY The ability to do work

4. WORK A change in energy

5. WorkEnergy

6. Circular Definition!

7. Radiant Electrical Chemical Thermal Nuclear Magnetic Sound Mechanical

10. At home – check out http://www.youtube.com/watch?v=3ff_ AXVlo9U for the Singing Tesla Coil! http://www.youtube.com/watch?v=3ff_ AXVlo9U

15. Potential energy + Kinetic energy = Mechanical energy

16. Potential energy + Kinetic energy = Mechanical energy Example of energy changes in a swing or pendulum.

17. 2 Kinds of Mechanical Energy Kinetic energy (KE) Potential Energy (PE) –Gravitational PE (PE g ) –Elastic PE (PE elastic )

18. Kinetic Energy Energy due to motion KE = ½ mv 2

19. Potential Energy Energy due to position

20. Bowling Ball – Conservation of Energy

21. Conserving Energy

27. Gravitational PE PE g = mgh

28. A 25 kg boy runs with a speed of 6.5 m/s. How much kinetic energy does the boy have? 530 Joules

29. How much potential energy does a 0.50 kg apple have if it hangs from a tree 13m above the ground? 64 Joules

30. A 220 gram fly has a kinetic energy of 55 Joules. How fast is the fly flying? 22 m/s

31. ENERGY IS CONSERVED!!

35. WORK W = F  s (Work = Force x displacement) Units: Joule (J) = N · m

36. Work is done only when components of a force are parallel to a displacement.

37. Force helps motion Positive Work Force opposes motion Negative Work Force 90 ° to motion No work Object not in motion No work

38. A student drags his book bag 15 meters across the classroom by pulling on it with a force of 5.0 Newtons. How much work does the student do on the bag? 75 Joules

39. Larry carries his 35N physics book across the room 25m away. How much work does he do on the book? 0 Joules

40. Work-Kinetic Energy Theorem W net =  KE

43. POWER The rate at which work is done

44. P= W tt Or…

45. P=  tt Or…

46. P= PP tt Or…

47. P = Fv = Force * velocity

48. The SI unit of power is the Watt, named in honor of James Watt James Watt James Watt James Watt. One Watt, W, of power is the power achieved when 1.0 J of work is done or 1.0 J of energy is transferred in a time of 1.0 s.

49. Watt = 1 J/s Horsepower (hp) = 746 W Unit of Power

50. How much power is generated by a motor that can lift a 5300 kg crate of bricks with a velocity of 15 m/s? 780,000 W

51. How much power is generated by a car engine that does 5500 Joules of work in 35 seconds? 160 W

52. How long will it take a 36 Watt motor to pull a box across the floor 25 m with a force of 16 N? 11 s

53. Homework: Chapter 8, Hewitt: Read 8.1-8.6 Do RQ 1-13; P&C 1-3,5-7; T&E 3-8; T&S 1-4