Chapter Introduction Lesson 1 Work and Power Lesson 2 Using Simple Machines Chapter Wrap-Up

1. Chapter Introduction Lesson 1 Work and Power Lesson 2 Using Simple Machines Chapter Wrap-Up

2. How do machines make doing work easier?

3. Work and Power • Essential Questions • What is the relationship between work, power and efficiency?

4. Work and Power • Work • Power • Efficiency

5. What is work? • In science, work is what is necessary for a force to move an object through a distance. • Work is calculated by multiplying the force applied to an object by the distance the object moves.

6. What is work? (cont.) • In order for you to do work, two things must occur: • You must apply a force to an object. • The object must move in the same direction as your applied force.

7. What is work? (cont.) • Is work being done? • Pushing a grocery cart in a store? • Yes, because the cart is moving in the same direction as the force (push). • Standing and holding a bag of groceries? • No, Although you are applying a force to the grocery bag by holding it, the grocery bag is not moving so no work is done.

8. What is work? (cont.) • Work is important in science because it is related to energy. • Work done when you lift an object which also increases the object’s energy. • Moving objects have kinetic energy • Gravitational Potential Energy (GPE) of an object increases as its height above the ground increases.

9. What is work? (cont.) • Doing work on a tray transfers energy to the tray. The added energy can be either kinetic energy or potential energy.

10. How is work measured? (cont.) • Work is equal to the force of a push or a pull multiplied by the distance the object is moved. • The product of force and distance has the unit newton·meter. The newton·meter is also known as the joule (J).

11. How is work measured? (cont.)

12. How is work measured? (cont.) • The work done on an object depends on the direction of the force applied and the direction of the motion. Motion of bed Applied Force

13. How is work measured? (cont.) • Now think of a box being pulled by a rope. • In this scenario, the applied force is at an angle (from your arm to the rope). The applied force has a horizontal part and a vertical part. Applied force Vertical force Motion of the box Horizontal force

14. How is work measured? (cont.) • When the applied force and the motion of the object are NOT in the same direction, only the part of the force that is in the same direction as the motion of the object is used in the work equation. • The vertical part of the applied force does no work on the box because it is not in the same direction as the motion of the box. Vertical force Motion of the box Horizontal force

15. How is work measured? (cont.) • The work done to lift an object equals the weight of the object multiplied by the distance it is lifted. • Work = weight x distance

16. What is power? • Power is the amount of work done per unit of time. • You can also think of power as how fast energy is transferred to an object.

17. What is power?(cont.) • You can calculate power by dividing the work done by the time needed to do the work. • Power is expressed in joules per second(J/s). One Joule per second is also know as a watt (W).

18. What is power?(cont.)

19. What is efficiency? • A machine is any device that makes doing something easier. • Some machines are simple and other machines are more complex.

20. The force you apply to a machine is the input force. The machine changes the input force to an output force. What is efficiency? (cont.) Output force Input force

21. The amount of input force multiplied by the distance over which the input force is applied is the input work. Winput = Finput x dinput What is efficiency? (cont.) Distance applied Input force

22. Machines convert input work to output work by applying an output force on something and making it move. Woutput = Foutput x distanceoutput What is efficiency? (cont.) Output distance Output force

23. The output work done by a machine never exceeds the input work because of friction. Friction converts some of the input work to thermal energy. What is efficiency? (cont.)

24. Efficiency is the ratio between the work done by a machine and the work put into it. Because output work is always less than input work, a machine’s efficiency is always less than 100 percent. Ex. Elevators are 85% efficient, car motors are 17% efficient What is efficiency? (cont.)

25. What is efficiency? (cont.)

26. When you lift an object, what else are you doing? A. decreasing the object’s energy B. increasing the object’s energy C. making the object do work D. receiving the object’s energy

27. Which is the rate at which work is done? A. energy B. force C. power D. work

28. To calculate the work done lifting an object, which is multiplied by the weight of the object? A. distance the object is lifted B. energy used to lift the object C. force applied to the object D. power needed to lift the object

29. Using Simple Machines • Essential Question • What is the relationship between work input and work output in a simple machine?

30. Using Simple Machines • Simple machine • Mechanical advantage • Lever • Fulcrum Wheel and axle Pulley Inclined plane Screw Wedge

31. What is a simple machine? • Simple machine is a device with few, if any, moving parts that makes it easier to do work. • Ex. screwdriver • A machine makes work easier by changing the size of the force, the distance the force acts, or the direction of a force.

32. What is a simple machine? (cont.) • The two main classes of simple machines are the lever and the inclined plane. • Lever class includes: • Wheel and axle and the pulley

33. What is a simple machine? (cont.) • Inclined plane includes: • Wedge and screw

34. What is a simple machine? (cont.) • Mechanical advantage is the number of times a simple machine multiplies an effort force.

35. What is a simple machine? (cont.) • Mechanical advantage can be less than 1, equal to 1, or greater than 1. • A mechanical advantage greater than 1 means the output force is greater than the input force.

36. What is a simple machine? (cont.)

37. What are the three kinds of levers? • Lever is a simple machine consisting of a bar and a pivot point. • Fulcrumis the pivot point in a lever. • The part of the bar on which a person applies an effort force is called the effort arm.

38. What are the three kinds of levers? (cont.) • The part of the bar on which the lever produces an output force is called the resistance arm. • The position of the fulcrum, the effort arm and the resistance arm vary among levers.

39. In a first-class lever, the fulcrum is between the input force and the output force. The direction of the input force is opposite the direction of the output force. When the effort arm is longer than the resistance arm, the output force is greater than the effort force What are the three kinds of levers? (cont.)

40. Your neck is an example of a first-class lever. What are the three kinds of levers? (cont.)

41. A second-class lever has the output force between the input force and the fulcrum. The output force and the input force act in the same direction. A second-class lever makes the output force greater than the input force. What are the three kinds of levers? (cont.)

42. A wheel barrow is an example of a second-class lever. What are the three kinds of levers? (cont.)

43. A third-class lever has the input between the output force and the fulcrum. The output force is less than the input force. Both the input force and the output force act in the same direction. What are the three kinds of levers? (cont.)

44. A fishing rod is an example of a third-class lever. What are the three kinds of levers? (cont.)

45. The ideal mechanical advantage of a lever equals the length of the input arm divided by the length of the output arm. What are the three kinds of levers? (cont.)

46. What are the three kinds of levers? (cont.)

47. What other machines are like levers? • Wheel and axle is a simple machine that consists of a wheel that applies an effort force and a smaller axle that produces an output force. • Mechanical advantage of a wheel and axle is calculated by dividing the length of the effort arm by the length of the resistance arm.

48. For a wheel and axle, the length of the input arm is the radius of the wheel and the length of the output arm is the radius of the axle. A screwdriver is a wheel and axle. The handle is the wheel and the shaft is the axle. What other machines are like levers? (cont.)

49. A wheel and axle can also make work easier in another way. If the radius of the wheel is smaller than the radius of the axle, the output distance is increased and the output force is decreased. Ex. Helicopters and ceiling fans. What other machines are like levers? (cont.)

50. Pulley is a grooved wheel that turns by the action of a rope in the groove. What other machines are like levers? (cont.) • In a pulley, the rope forms the arms and the wheel serves as the fulcrum.