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Work and Machines: Understanding the Basics

This chapter explores the concept of work and how machines can make work easier. It covers the different types of machines, including inclined planes, wedges, screws, levers, wheel and axles, and pulleys. The chapter also discusses mechanical advantage and efficiency of machines, as well as their applications in the human body and compound machines.

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Work and Machines: Understanding the Basics

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  1. Chapter 12 Work and Machines

  2. Section 1 - What is work? • Work is done on an object when the object moves in the same direction in which the force is exerted. • Work - The product of force and distance when a force is used to move an object. • No work without motion Chapter 12

  3. Section 1 - What is work? • The amount of work done on an object can be determined by multiplying force times distance. • Work = Force x Distance • work units - Joules (J) Chapter 12

  4. Section 1 - What is work? • Power is the rate at which work is done. • Power equals the amount of work done on an object in a unit of time. Chapter 12

  5. Section 1 - What is work? • Power = Joules/second = watt (W) • kW = 1,000 W • 1 horsepower = 746 W Chapter 12

  6. Section 2 -How Machines Do Work • Machine - • A device that changes the amount of force exerted or the direction in which force is exerted. • A device with which you can do work in a way that is easier or more effective. • A machine makes work easier by changing at least one of three factors. A machine may change the amount of force you exert, the distance over which you exert your force, or the direction in which you exert your force. Chapter 12

  7. Section 2 -How Machines Do Work • pg.415 • Increase force, decrease distance • Increase distance, decrease force • Change direction Chapter 12

  8. Section 2 -How Machines Do Work • A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. Chapter 12

  9. Section 2 -How Machines Do Work • Friction reduces mechanical advantage • The efficiency of a machine compares the output work to the input work. • Efficiency is expressed as a percent. • Efficiency = output work/input work x 100% • Problems on page 418 Chapter 12

  10. Section 3 - Simple Machines • Six types of machines • Inclined plane • Wedge • Screw • Lever • Wheel & axle • Pulley Chapter 12

  11. Inclined Plane • An inclined plane is a flat sloped surface. • Less force exerted over longer distance Chapter 12

  12. Inclined Plane • You can determine the ideal mechanical advantage of an inclined plane by dividing the length of the incline by its height. • Ideal Mechanical Advantage= Length of incline/ Height of incline. Chapter 12

  13. Wedge • A wedge is a device that is thick at one end and tapers to a thin edge at the other end. • Less force exerted over longer distance Chapter 12

  14. Wedge • The ideal mechanical advantage of a wedge is determined by dividing the length of the wedge by its width. Chapter 12

  15. Screw • Inclined plane wrapped around a cylinder • Less force Chapter 12

  16. Screw • The ideal mechanical advantage of a screw is the length around the threads divided by length of the screw. Chapter 12

  17. Lever • A lever is a rigid bar that is free to pivot, or rotate, on a fixed point. • Fulcum - the fixed point that a lever pivots around Chapter 12

  18. Lever • The ideal mechanical advantage of a lever is determined by dividing the distance from the fulcrum to the input force by the distance from the fulcrum to the output force. • Ideal mechanical advantage = Distance from fulcrum to input force / Distance from fulcrum to output force Chapter 12

  19. 3 Types of Levers Chapter 12

  20. Wheel and Axle • A wheel and axle is a simple machine made of two circular or cylindrical objects fastened together that rotate about a common axis. Chapter 12

  21. Wheel and Axle • Less force exerted over longer distance • Doorknob Chapter 12

  22. Wheel and Axle • You can find the ideal mechanical advantage of a wheel and axle by dividing the radius of the wheel by the radius of the axle. • Mechanical advantage = Radius of wheel / Radius of axle Chapter 12

  23. Pulley • A pulley is made of a grooved wheel with rope or cable wrapped around it. • Change amount and direction of input force Chapter 12

  24. Pulley • The ideal mechanical advantage of a pulley is equal to the number of sections of rope that support the object. Chapter 12

  25. Section 4 - Machines in the human body • Lifting levers - most of the machines in your body are levers that consist of bones and muscles. • Pg.432 Levers in the body • Wedges - front teeth (incisors) • Break toothpick in fingers Chapter 12

  26. Compound Machines • A compound machine is a machine that utilizes two or more simple machines. • The ideal mechanical advantage of a compound machine is the product of the individual ideal mechanical advantages of the simple machines that make it up. Chapter 12

  27. work, machine, efficiency, mechanical advantage, inclined plane, wedge, screw, lever, fulcrum, wheel and axle, pulley Ch. 12 Vocabulary Chapter 12

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