3. Warm Up 5/2/12 1. What is the first law of motion? 2. Which formula is associated with the 2 nd law of motion? 3. What is the first thing to come to your mind when you hear the word work, power and energy?

4. Announcements You will have a unit test on Motion and Forces next Friday If you have any make up work you need to get it to me by Friday, May 4 th if you want it reflected on your upcoming progress report.

5. What is work? Work is the use of force to move an object. In scientific terms, you only do work when you use force to move something.

6. How do we calculate work? Work= force X distance OR W= FD The unit that we use to measure work is Joule (J) or the Newton-meter

7. Example 1 How much work is done if a person lifts a barbell weighing 500 N to a height of 2 m?

8. Answer Formula for work is W=FD W=? F=500 N D=2 m W= 500/2 W=250 J

9. Other formulas If you have to calculate distance: D= W/F The unit is meters If you have to calculate force: F= W/d The unit is Newton’s

10. Guided Practice Problems 1. If you push a cart with force of 70 N for 2 M, how much work is done? 2. If you did 200 J of work pushing a box with a force of 40 N, how far did you push the box? 3. If you get a flat tire and have to push a car 3 M and apply a force of 3 N, how much work did you do? 4. How much force is needed to move a tractor trailer if a machine is only allowed to use 4 J of work and it has to move 25 M.

11. Who or what does work? Just as you do work when you pick up a book or write in your notebook, objects can also do work. For example, cars do work when the move down the road, or bowling balls do work when they hit pins.

12. Independent Practice 1. If you push very hard on an object but it does not move, have you done work? Explain why or why not. 2. What two factors do you need to know to calculate how much work was done in any situation? 3. Was work done on a book that fell from a desk to the floor? If so what force was involved? 4. Work is done on a ball when a soccer player kicks it. is the player still doing work on the ball as it is rolls across the ground? 5. Tina lifted a box 0.5 M. the box weighed 25 N. how much work did Tina do?

13. Answers 1. No, the object must move for work to be done. 2. Force and distance. 3. Yes, the force of gravity. 4. No: the player is no longer exerting force on the ball. 5. W= FD = 25 N x 0.5 m = 12.5 J

14. Warm Up 5/3/12 1. What is the formula for work? 2. What unit do we use for work? 3. Can objects do work or just people? Be sure to explain your answer.

15. Announcements Any missing work that you want reflected on the upcoming progress report must be given to me by tomorrow. Do not hand it to me or place it on my desk….on your way out of my room, please place it in the late work bin.

16. 15 Power Power is the rate at which work is done. Power = Work / Time The unit of power is the watt.

17. 16 Check for Understanding 1.Two physics students, Ben and Bonnie, are in the weightlifting room. Bonnie lifts the 50 kg barbell over her head (approximately.60 m) 10 times in one minute; Ben lifts the 50 kg barbell the same distance over his head 10 times in 10 seconds. Which student does the most work? Which student delivers the most power? Explain your answers.

18. 17 Ben and Bonnie do the same amount of work; they apply the same force to lift the same barbell the same distance above their heads. Yet, Ben is the most powerful since he does the same work in less time. Power and time are inversely proportional.

19. 18 2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Force=10 x 2 Force=20 N Work=Force x Distance Work = 20 x 10 Work = 200 Joules Power = Work/Time Power = 200/5 Power = 40 watts

20. 19 2. How much power will it take to move a 10 kg mass at an acceleration of 2 m/s/s a distance of 10 meters in 5 seconds? This problem requires you to use the formulas for force, work, and power all in the correct order. Force=Mass x Acceleration Work=Force x Distance Power = Work/Time

21. Example 1 An explorer uses 6000 J of work to pull his sled for 60 seconds. What power does he need?

22. Answer P= w/t P= 6000 j/60 s P= 100 W

23. Practice Problems 1. If a conveyor belt uses 10 J to move a piece of candy a distance of 3 m in 20 s, what is the conveyor belt’s power? 2. An elevator uses a force of 1710 N to lift 3 people up 1 floor. Each floor is 4 m high. The elevator takes 8 s to lift the 3 people up 2 floors. What is the elevators power?

24. Solutions to practice problems 1. P= w/t P= 10 J/20 s = 0.5 j/s P= 0.5 W 2. P= w/t W= fd P=1710 N x 8 m 8 s P= 1710 W

25. 24 History of Work Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

26. Does this sound familiar? If you think about cars, they use the unit horsepower. Horsepower is the amount of work a horse can do in a minute. We still use this unit as long ago, many people used horses to do work.

27. Independent Practice 1. How is power related to work? 2. What do you need to know to calculate how much energy a light bulb uses? 3. Which takes more power: using 15 N to lift a ball in 5 seconds or using 100 N to push a box 2 m in 1 minute?

28. Answers 1. Power is the rate at which work is done. The faster you do work, the greater your power. 2. Power can be measured in joules per second (watts) or in horsepower. Examples will vary but might include light bulbs for watts and cars for horsepower. 3. Using 15 N to lift a ball 2 m in 5 seconds.

29. Warm Up 5/4/12 1. What is power? 2. How do you calculate power? 3. What unit do we use to calculate power?

30. Announcements All make up work due today. Please put it in the late work bin on your way out today Check the no name folder to see if you have work there. It will be thrown away today @ 4:15.

31. Energy This is the ability to do work. Work transfers energy. There are three different types of energy: 1. Potential energy 2. Kinetic energy 3. Mechanical energy

32. Kinetic energy This is energy in motion. For example, when you throw a ball you transfer energy and it moves. By doing work on the ball (throwing it), you give it kinetic energy. Formula: KE= 1/2mv 2

33. Potential energy This is stored energy or the energy that an object has due to its position or shape. For example, when you do work to lift a ball from the ground you give the ball potential energy. Why? Because it has the “potential” to be thrown or fall back to the ground.

34. Mechanical energy Is the energy possessed by an object due to its position or motion. Or ME= PE + KE

35. Example of Kinetic Energy What is the kinetic energy of a girl who as a mass of 40 kg and a velocity of 3 m/s? Remember: KE= 1/2mv 2

36. Answer KE= ½ mv 2 = ½ x 40 kg x (3 m/s) 2 =360kg 2s =180 J

37. Other types of energy Heat energy Heat energy Nuclear energy Electromagnetic energy Electromagneticenergy

38. Independent Practice Answer the following questions below: 1. How is water used to generate electricity? 2. Describe the pro’s and con’s of nuclear energy? 3. How can we use heat as energy? Once you are done: Create a cartoon that describes the different types of energy. For each type identify the potential when energy is considered potential and kinetic.

39. Stations Station nameWhat type of energy does it provide? Where do we get it from? Examples of places, ways this energy is used Brief summary of the station Thermal energy Chemical energy Nuclear energy Electromagnetic energy

40. Warm Up 5/7/12 1. Explain the relationship between work and energy. 2. What is the formula for kinetic energy? 3. What is the formula for mechanical energy? 4. Briefly explain the difference between potential and kinetic energy.

41. Announcements Be sure to turn in homework

42. 41 Simple Machines Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

43. 42 Simple Machines The six simple machines are: Lever Wheel and Axle Pulley Inclined Plane Wedge Screw

44. 43 Simple Machines A machine is a device that helps make work easier to perform by accomplishing one or more of the following functions: transferring a force from one place to another, changing the direction of a force, increasing the magnitude of a force, or increasing the distance or speed of a force.

45. 44 Mechanical Advantage It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task). When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.

46. 45 Mechanical Advantage Mechanical advantage is the ratio of output force divided by input force. If the output force is bigger than the input force, a machine has a mechanical advantage greater than one. If a machine increases an input force of 10 pounds to an output force of 100 pounds, the machine has a mechanical advantage (MA) of 10. In machines that increase distance instead of force, the MA is the ratio of the output distance and input distance. MA = output/input

47. 46 No machine can increase both the magnitude and the distance of a force at the same time.

48. 47 The Lever A lever is a rigid bar that rotates around a fixed point called the fulcrum. The bar may be either straight or curved. In use, a lever has both an effort (or applied) force and a load (resistant force).

49. 48 The 3 Classes of Levers The class of a lever is determined by the location of the effort force and the load relative to the fulcrum.

50. 49

51. 50 To find the MA of a lever, divide the output force by the input force, or divide the length of the resistance arm by the length of the effort arm.

52. 51 First Class Lever In a first-class lever the fulcrum is located at some point between the effort and resistance forces. Common examples of first-class levers include crowbars, scissors, pliers, tin snips and seesaws. A first-class lever always changes the direction of force (I.e. a downward effort force on the lever results in an upward movement of the resistance force).

53. 52 Fulcrum is between EF (effort) and RF (load) Effort moves farther than Resistance. Multiplies EF and changes its direction

54. 53 Second Class Lever With a second-class lever, the load is located between the fulcrum and the effort force. Common examples of second-class levers include nut crackers, wheel barrows, doors, and bottle openers. A second-class lever does not change the direction of force. When the fulcrum is located closer to the load than to the effort force, an increase in force (mechanical advantage) results.

55. 54 RF (load) is between fulcrum and EF Effort moves farther than Resistance. Multiplies EF, but does not change its direction

56. 55 Third Class Lever With a third-class lever, the effort force is applied between the fulcrum and the resistance force. Examples of third-class levers include tweezers, hammers, and shovels. A third-class lever does not change the direction of force; third-class levers always produce a gain in speed and distance and a corresponding decrease in force.

57. 56 EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort. Multiplies the distance the effort force travels

58. 57 Wheel and Axle The wheel and axle is a simple machine consisting of a large wheel rigidly secured to a smaller wheel or shaft, called an axle. When either the wheel or axle turns, the other part also turns. One full revolution of either part causes one full revolution of the other part.

59. 58 Pulley A pulley consists of a grooved wheel that turns freely in a frame called a block. A pulley can be used to simply change the direction of a force or to gain a mechanical advantage, depending on how the pulley is arranged. A pulley is said to be a fixed pulley if it does not rise or fall with the load being moved. A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage. A moveable pulley rises and falls with the load that is being moved. A single moveable pulley creates a mechanical advantage; however, it does not change the direction of a force. The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley.

60. 59 Inclined Plane An inclined plane is an even sloping surface. The inclined plane makes it easier to move a weight from a lower to higher elevation.

61. 60 Inclined Plane The mechanical advantage of an inclined plane is equal to the length of the slope divided by the height of the inclined plane. While the inclined plane produces a mechanical advantage, it does so by increasing the distance through which the force must move.

62. 61 Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work. A B C

64. 63 Wedge The wedge is a modification of the inclined plane. Wedges are used as either separating or holding devices. A wedge can either be composed of one or two inclined planes. A double wedge can be thought of as two inclined planes joined together with their sloping surfaces outward.

65. 64 Screw The screw is also a modified version of the inclined plane. While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).

66. 65 MA of an screw can be calculated by dividing the number of turns per inch.

67. 66

68. 67 Efficiency We said that the input force times the distance equals the output force times distance, or: We said that the input force times the distance equals the output force times distance, or: Input Force x Distance = Output Force x Distance However, some output force is lost due to friction. The comparison of work input to work output is called efficiency. The comparison of work input to work output is called efficiency. No machine has 100 percent efficiency due to friction. No machine has 100 percent efficiency due to friction.

69. 68 Practice Questions 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? 3. Using a single fixed pulley, how heavy a load could you lift ?

70. 69 Practice Questions 4. Give an example of a machine in which friction is both an advantage and a disadvantage. 5. Why is it not possible to have a machine with 100% efficiency? 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.

71. 70 Practice Questions 1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work. 2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W 3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.

72. 71 Practice Questions 4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency. 5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient. 6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.