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Table of Contents

Work and Machines. Chapter M4. Table of Contents. Section 1 Work and Power Section 2 What Is a Machine? Section 3 Types of Machines. Section 1 Work and Power. Chapter M4. Objectives. Determine when work is being done on an object. Calculate the amount of work done on an object.

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  1. Work and Machines Chapter M4 Table of Contents Section 1 Work and Power Section 2 What Is a Machine? Section 3 Types of Machines

  2. Section1 Work and Power Chapter M4 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.

  3. Section1 Work and Power Chapter M4 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.

  4. Section1 Work and Power Chapter M4 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.

  5. Section1 Work and Power Chapter M4

  6. Section1 Work and Power Chapter M4 How Much Work? • Same Work, Different ForceWork depends on distance as well as force.

  7. Section1 Work and Power Chapter M4 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: W F  d • The unit used to express work is the newton-meter (N  m), which is more simply called thejoule.

  8. Section1 Work and Power Chapter M4

  9. Section2 What Is a Machine? Chapter M4 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.

  10. Section2 What Is a Machine? Chapter M4 Machines: Making Work Easier • Amachineis a device that makes work easier by changing the size or direction of a force.

  11. Section2 What Is a Machine? Chapter M4 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 Help Machines allow force to be applied over a greater distance, which means that less force will be needed for the same amount of work.

  12. Section2 What Is a Machine? Chapter M4 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.

  13. Section2 What Is a Machine? Chapter M4

  14. output force mechanical advantage ( MA ) = input force Section2 What Is a Machine? Chapter M4 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:

  15. work output mechanical efficiency  100 = work input Section2 What Is a Machine? Chapter M4 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:

  16. Section2 What Is a Machine? Chapter M4 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.

  17. Section3 Types of Machines Chapter M4 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.

  18. Section3 Types of Machines Chapter M4 Levers • Aleveris a simple machine that has a bar that pivots at a fixed point, called a fulcrum. • First-Class Levers With a first-class lever, the fulcrum is between the input force and the load.

  19. Section3 Types of Machines Chapter M4 Levers, continued • Second-Class LeversThe load of a second-class lever is between the fulcrum and the input force.

  20. Section3 Types of Machines Chapter M4 Levers, continued • Third-Class LeversThe input force in a third-class lever is between the fulcrum and the load.

  21. Section3 Types of Machines Chapter M4 Pulleys • Apulleyis a simple machine that consists of a wheel over which a rope, chain, or wire passes. • Fixed Pulleys A fixed pulley is attached to something that does not move.

  22. Section3 Types of Machines Chapter M4 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.

  23. Section3 Types of Machines Chapter M4 Pulleys, continued

  24. Section3 Types of Machines Chapter M4 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.

  25. Section3 Types of Machines Chapter M4 Inclined Planes • Aninclined planeis a simple machine that is a straight, slanted surface. • Mechanical Advantage of an Inclined Plane The 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.

  26. Section3 Types of Machines Chapter M4 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.

  27. Section3 Types of Machines Chapter M4 Inclined Planes, continued • Screws A 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.

  28. Section3 Types of Machines Chapter M4 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.

  29. Work and Machines Chapter M4 Concept Map Use the terms below to complete the concept map on the next slide.

  30. Work and Machines Chapter M4

  31. Work and Machines Chapter M4

  32. End of Chapter M4 Show

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