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Work and Machines What Is Work? How Machines Do Work Simple Machines Table of Contents.

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Presentation on theme: "Work and Machines What Is Work? How Machines Do Work Simple Machines Table of Contents."— Presentation transcript:

1 Work and Machines What Is Work? How Machines Do Work Simple Machines Table of Contents

2 Work and Machines - What Is Work? The Meaning of Work Work is done on an object when the object moves in the same direction in which the force is exerted. To do work on an object: The object must move when force is applied. The object must move in the same direction as the force.

3 Work and Machines Calculating Work and Power - What Is Work? Force is measured in Newtons (N). Formula for Work: Work = Force x Distance The SI unit of measure for work is joule (J), in honor of James Prescott Joule, who studied work in the mid-1800s. Formula for Power: Power = Work ORForce x Distance Time Time The SI unit of measure for power is Watts (W), in honor of James Watt who greatly improved the steam engine.

4 Work and Machines Calculating Power A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck? Read and Understand What information have you been given? Force of the tow truck (F) = 11,000 N Distance (d) = 5.0 m Time (t) = 25 s - What Is Work?

5 Work and Machines Calculating Power A tow truck exerts a force of 11,000 N to pull a car out of a ditch. It moves the car a distance of 5 m in 25 seconds. What is the power of the tow truck? Plan and Solve What quantity are you trying to calculate? The Power (P) the tow truck uses to pull the car = __ What formula contains the given quantities and the unknown quantity? Power = (Force X Distance)/Time Perform the calculation. Power = (11,000 N X 5.0 m)/25 s Power = (55,000 Nm)/25 s or 55,000 J/25 s Power = 2,200 J/s = 2,200 W - What Is Work?

6 Work and Machines Calculating Power Practice Problem A motor exerts a force of 12,000 N to lift an elevator 8.0 m in 6.0 seconds. What is the power produced by the motor? 16,000 W or 16 kW - What Is Work?

7 Work and Machines QuestionAnswer Asking Questions Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions. What is work? Work is done when an object moves in the same direction in which the force is exerted. How can you calculate work? Work = Force X Distance What is power?Power is the rate at which work is done. - What Is Work?

8 Work and Machines - How Machines Do Work Input and Output Work The amount of input work done by the gardener equals the amount of output work done by the shovel. Input force – effort you put into the machine. Output force – effort the machine puts into an object.

9 Work and Machines - How Machines Do Work What Is a Machine? A machine makes work easier by changing at least one of three factors: The amount of force you exert The distance over which you exert your force The direction in which you exert your force. Ex. A ramp or faucet Ex. Hockey stick, chopsticks, riding a bike Ex. A weight machine with pulleys

10 Work and Machines Efficiency Efficiency determines how much work was wasted due to friction. Efficiency = Output Work x 100% Input Work The higher the percentage, the more efficient the machine (wastes little work). An ideal machine would have 100% efficiency. - How Machines Do Work

11 Work and Machines Mechanical Advantage The input force and output force for three different ramps are shown in the graph. - How Machines Do Work Mechanical advantage = Output force Input force

12 Work and Machines Mechanical Advantage Input force Reading Graphs: What variable is plotted on the horizontal axis? - How Machines Do Work

13 Work and Machines Mechanical Advantage 400 N Interpreting Data: If an 80-N input force is exerted on Ramp 2, what is the output force? - How Machines Do Work

14 Work and Machines Main Idea Detail Identifying Main Ideas As you read the section “What Is a Machine?” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea. The mechanical advantage of a machine helps by… changing the amount of force you exert changing the distance over which you exert your force changing the direction of the force - How Machines Do Work

15 Work and Machines Links on Mechanical Efficiency Click the SciLinks button for links on mechanical efficiency. - How Machines Do Work

16 Work and Machines End of Section: How Machines Do Work

17 Work and Machines - Simple Machines Inclined Plane An inclined plane is a flat, sloped surface. Ideal mechanical advantage = Length of incline Height of incline

18 Work and Machines - Simple Machines Wedge A wedge is a device that is thick at one end and tapers to a thin edge at the other end. Ideal Mechanical Advantage = Length of Wedge Width of Wedge

19 Work and Machines - Simple Machines Screws A screw can be thought of as an inclined plane wrapped around a cylinder. I.M.A. = Length around the threads Length of the screw

20 Work and Machines - Simple Machines Levers A lever is a ridged bar that is free to pivot, or rotate, on a fixed point (fulcrum). I.M.A. = Distance from fulcrum to input force Distance from fulcrum to output force

21 Work and Machines - Simple Machines Levers Levers are classified according to the location of the fulcrum relative to the input and output forces.

22 Work and Machines - Simple Machines 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. I.M.A. = Radius of wheel Radius of axle

23 Work and Machines - Simple Machines Pulley A pulley is a simple machine made of a grooved wheel with a rope or cable wrapped around it. I.M.A. = Number of sections of rope that support the object

24 Work and Machines - Simple Machines Simple Machines in the Body Most of the machines in your body are levers that consist of bones and muscles. Your teeth are wedges.

25 Work and Machines - Simple Machines Compound Machines A compound machine is a machine that utilizes two or more simple machines. I.M.A. = The product of the individual I.M.A.s of the simple machines that make it up.

26 Work and Machines Previewing Visuals Before you read, preview Figure 17. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions. Three Classes of Levers Q. What are the three classes of levers? A. The three classes of levers are first-class levers, second-class levers, and third-class levers. Q. How do the three classes of levers differ? A. They differ in the position of the fulcrum, input force, and output force. - Simple Machines

27 Work and Machines Levers Click the Video button to watch a movie about levers. - Simple Machines

28 Work and Machines Pulleys Click the Video button to watch a movie about pulleys. - Simple Machines

29 Work and Machines End of Section: Simple Machines

30 Work and Machines Graphic Organizer Wheel and axle Simple Machine Mechanical Advantage Example Inclined plane Length of incline ÷ Height of incline Ramp Radius of wheel ÷ Radius of axle Screwdriver Wedge Length of wedge ÷ Width of wedge Ax Screw Length around threads ÷ Length of screw Screw Lever Distance from fulcrum to input force ÷ Distance from fulcrum to output force Seesaw Pulley Number of sections of supporting rope Flagpole

31 Work and Machines End of Section: Graphic Organizer


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