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# How to Use This Presentation

How to Use This Presentation. How to Use This Presentation. • To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show” , or simply press F5 on the top row of your keyboard.

## How to Use This Presentation

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1. How to Use This Presentation How to Use This Presentation • To View the presentation as a slideshow with effects select “View” on the menu bar and click on “Slide Show”, or simply press F5 on the top row of your keyboard. • To advance to the next slide click the left mouse button once. • From the Chapter screen you can click on any section to go directly to that section’s presentation. • Blank or “missing” areas of a slide will remain hidden until the left mouse button is clicked. • You may exit the slide show at any time by pressing the Esc key.

2. Resources Bellringers Chapter Presentation Transparencies Standardized Test Prep Image and Math Focus Bank CNN Videos Visual Concepts

3. Work and Machines Chapter 8 Table of Contents Section 1 Work and Power Section 2 What Is a Machine? Section 3 Types of Machines

4. Chapter 8 Section1 Work and Power Bellringer • First, in your science journal, define what specific kind of work is being done in each activity below. Then, select the activities that require the least amount of work. • carrying heavy books home • reading a 300-page novel • skiing for 1 hour • lifting a 45 kg mass • holding a steel beam in place for 3 hours • jacking up a car

5. Chapter 8 Section1 Work and Power Objectives • Determine when work is being done on an object. • Calculate the amount of work done on an object. • Explain the difference between work and power.

6. Section1 Work and Power Chapter 8 What Is Work? • Workis the transfer of energy to an object by using a force that causes the object to move in the direction of the force. • Transfer of EnergyOne way you can tell that work is being done is that energy is transferred.

7. Section1 Work and Power Chapter 8 What Is Work?, continued • Difference Between Force and WorkApplying a force doesn’t always result in work being done. • Force and Motion in the Same DirectionFor work to be done on an object, the object must move in the same direction as the force.

8. Chapter 8 Section1 Work and Power

9. Section1 Work and Power Chapter 8 How Much Work? • Same Work, Different ForceWork depends on distance as well as force.

10. Section1 Work and Power Chapter 8 How Much Work?, continued • Calculating WorkThe amount of work (W) done in moving an object can be calculated by multiplying the force (F) applied to the object by the distance (d) through which the force is applied: • Work = force x distance W F  d • The unit used to express work is the newton-meter (N  m), which is more simply called thejoule.

11. Chapter 8 Section1 Work and Power

12. W P = t † Chapter 8 Section1 Work and Power Power: How Fast Work Is Done • Calculating PowerPower is the rate at which energy is transferred. To calculate power (P), you divide the amount of work done (W) by the time (t) it takes to do that work: • Power = work/time • The unit used to express power is joules per second (J/s), also called the watt. One watt (W) is equal to 1 J/s.

13. Section1 Work and Power Chapter 8

14. Section1 Work and Power Chapter 8 Power: How Fast Work Is Done, continued • Increasing PowerIt may take you longer to sand a wooden shelf by hand than by using an electric sander, but the amount of energy needed is the same either way. Only the power output is lower when you sand the shelf by hand.

15. Section2 What Is a Machine? Chapter 8 Bellringer • Write a one-paragraph answer in your science journalto the following question: • Why do we use machines?

16. Section2 What Is a Machine? Chapter 8 Objectives • Explainhow a machine makes work easier. • Describe and give examples of the force-distance trade-off that occurs when a machine is used. • Calculate mechanical advantage. • Explain why machines are not 100% efficient.

17. Section2 What Is a Machine? Chapter 8 Machines: Making Work Easier • Amachineis a device that makes work easier by changing the size or direction of a force.

18. Section2 What Is a Machine? Chapter 8 Machines: Making Work Easier, continued • Work In, Work OutThe work that you do on a machine is called work input. The work done by the machine on an object is called work output. • How Machines HelpMachines allow force to be applied over a greater distance, which means that less force will be needed for the same amount of work.

19. Section2 What Is a Machine? Chapter 8 Machines: Making Work Easier, continued • Same Work, Different ForceMachines make work easier by changing the size or direction of the input force. • The Force-Distance Trade OffWhen a machine changes the size of the force, the distance through which the force is exerted must also change.

20. Section2 What Is a Machine? Chapter 8

21. output force mechanical advantage ( MA ) = input force Section2 What Is a Machine? Chapter 8 Mechanical Advantage • What Is Mechanical Advantage?A machine’s mechanical advantage is the number of times the machine multiplies force. • Calculating Mechanical AdvantageYou can find mechanical advantage by using the following equation:

22. work output mechanical efficiency  100 = work input Section2 What Is a Machine? Chapter 8 Mechanical Efficiency • The less work a machine has to do to overcome friction, the more efficient the machine is. Mechanical efficiency is a comparison of a machine’s work output with the work input. • Calculating EfficiencyA machine’s mechanical efficiency is calculated using the following equation:

23. Section2 What Is a Machine? Chapter 8 Mechanical Efficiency, continued • Perfect Efficiency?An ideal machine would be a machine that had 100% mechanical efficiency. • Ideal machines are impossible to build, because every machine has moving parts. Moving parts always use some of the work input to overcome friction.

24. Section2 What Is a Machine? Chapter 8 Mechanical Efficiency Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

25. Chapter 8 Section3 Types of Machines Bellringer • What type of machine can be found on at least half the students in this room right now? What kinds of machines were common 50 years ago? 100 years ago? Are any of the same machines around today that were common in the 1800s? What has changed about those same machines today? • Record your thoughts in your science journal.

26. Chapter 8 Section3 Types of Machines Objectives • Identify and give examples of the six types of simple machines. • Analyze the mechanical advantage provided by each simple machine. • Identify the simple machines that make up a compound machine.

27. Chapter 8 Section3 Types of Machines Levers • Aleveris a simple machine that has a bar that pivots at a fixed point, called a fulcrum. • First-Class LeversWith a first-class lever, the fulcrum is between the input force and the load.

28. Chapter 8 Section3 Types of Machines Levers, continued • Second-Class LeversThe load of a second-class lever is between the fulcrum and the input force.

29. Chapter 8 Section3 Types of Machines Levers, continued • Third-Class LeversThe input force in a third-class lever is between the fulcrum and the load.

30. Chapter 8 Section3 Types of Machines Pulleys • Apulleyis a simple machine that consists of a wheel over which a rope, chain, or wire passes. • Fixed PulleysA fixed pulley is attached to something that does not move.

31. Chapter 8 Section3 Types of Machines Pulleys, continued • Movable PulleysUnlike fixed pulleys, movable pulleys are attached to the object being moved. • Blocks and TacklesWhen a fixed pulley and a movable pulley are used together, the pulley system is called a block and tackle.

32. Chapter 8 Section3 Types of Machines Pulleys, continued

33. Chapter 8 Section3 Types of Machines Wheel and Axle • What Is a Wheel and Axle?A wheel and axle is a simple machine consisting of two circular objects of different sizes.

34. Chapter 8 Section3 Types of Machines Wheel and Axle, continued • Mechanical Advantage of a Wheel and AxleThe mechanical advantage of a wheel and axle can be found by dividing the radius (the distance from the center to the edge) of the wheel by the radius of the axle.

35. Chapter 8 Section3 Types of Machines Inclined Planes • Aninclined planeis a simple machine that is a straight, slanted surface. • Mechanical Advantage of an Inclined PlaneThe mechanical advantage (MA) of an inclined plane can be calculated by dividing the length of the inclined plane by the height to which the load is lifted.

36. Chapter 8 Section3 Types of Machines

37. Chapter 8 Section3 Types of Machines Inclined Planes, continued • WedgesA wedge is a pair of inclined planes that move. • Mechanical Advantage of Wedges can be found by dividing the length of the wedge by its greatest thickness.

38. Chapter 8 Section3 Types of Machines Inclined Planes, continued • ScrewsA screw is an inclined plane that is wrapped in a spiral around a cylinder. • Mechanical Advantage of ScrewsThe longer the spiral on a screw is and the closer together the threads are, the greater the screw’s mechanical advantage is.

39. Chapter 8 Section3 Types of Machines Compound Machines • What Are Compound Machines?Compound machines are machines that are made of two or more simple machines. • Mechanical Efficiency of Compound MachinesThe mechanical efficiency of most compound machines is low, because compound machines have more moving parts than simple machines do. Thus, there is more friction to overcome.

40. Section3 Types of Machines Chapter 8 Compound Machine Click below to watch the Visual Concept. You may stop the video at any time by pressing the Esc key. Visual Concept

41. Chapter 8 Work and Machines Concept Map Use the terms below to complete the concept map on the next slide.

42. Chapter 8 Concept Map

43. Chapter 8 Concept Map

44. End of Chapter 8 Show

45. Chapter 8 Work and Machines CNN Videos • Multicultural Connections: Who Built the Egyptian Pyramids? • Science, Technology, and Society: Snake Robots