1 / 31

Table of Contents

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

yagil
Télécharger la présentation

Table of Contents

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

  2. - 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. - What Is Work? Calculating Work and Power • 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 OR Force 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. 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? Calculating Power

  5. 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 N•m)/25 sor 55,000 J/25 s Power = 2,200 J/s = 2,200 W - What Is Work? Calculating Power

  6. 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? Calculating Power

  7. Question Answer - What Is Work? 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. Work is done when an object moves in the same direction in which the force is exerted. What is work? How can you calculate work? Work = Force X Distance What is power? Power is the rate at which work is done.

  8. - 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. - 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. 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 Efficiency

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

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

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

  14. - How Machines Do Work 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. Main Idea The mechanical advantage of a machine helps by… Detail Detail Detail changing the amount of force you exert changing the distance over which you exert your force changing the direction of the force

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

  16. End of Section:How Machines Do Work

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

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

  22. - 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. - 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. - 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. - 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. - Simple 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.

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

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

  29. End of Section:Simple Machines

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

  31. End of Section:Graphic Organizer

More Related