1 / 42

Work and Machines

Work and Machines. Chapter 3. Lesson 1- Work and Power. What is work? any time a force is exerted on an object that causes the object to move the object must move in the same direction in which the force is exerted. No movement of object = no work done no matter how much force is used.

archer
Download Presentation

Work and Machines

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. Work and Machines Chapter 3

  2. Lesson 1- Work and Power What is work? • any time a force is exerted on an object that causes the object to move • the object must move in the same direction in which the force is exerted. • No movement of object = no work done no matter how much force is used

  3. Different directions = NO WORK...

  4. Some work is done.

  5. Most work is done.

  6. How do you calculate work? Work = Force X Distance Work = (N) X (m) Work = _____ N.m Therefore the SI unit for Work is called a JOULE. (1 J = force of 1N to move an object a distance of 1 meter)

  7. 90N X 30 m = 2700 J (force X Distance) 180 N X 60 m = 10800 J ( 4 times more)

  8. What is Work Demonstration… Worksheet 71 with discussion

  9. What is Power? • the rate at which work is done • Power = Work Force X Distance Time Time • Unit for Power is watt • 1J/s = 1 W

  10. Pinwheel Demo… (15 seconds) • Is work done on the pinwheel? Explain. • How are the two situations different? • Which situation involved more power? Explain.

  11. Investigating Power: pg 72 You and your partner will be completing this investigation. Use your time wisely!

  12. Lesson 2 Understanding Machines

  13. Input force • This is the force you exert. • You exert this force over a specific distance. • (input work)

  14. Output Force • This is the force the machine exerts • The machine also moves a specific distance • (output work)

  15. Output distance and force

  16. What does a machine do? • Makes work easier by • changing the amount of force your exert OR • changing the distance over which you exert your force OR • changing the direction in which you exert your force

  17. Machines don’t change the amount of work you do, but they do change the way you do the work.

  18. Changing Force If a machine allows you to use less input force, you must apply that force over a greater distance.

  19. Changing Force Work = Force X Distance • Let’s Say: My force is 5 N and the distance is 2 m; • 5 N x 2 m = 10 J of work • If the amount of work stay the same, a decrease of force means an increase of distance. • If I put 2N of force, then my distance would be 5m to equal 10 J of work.

  20. Changing Distance If a machine allows you to move your input force over a shorter distance, than you need to apply a greater input force.

  21. Changing Distance Large output distance Large input force

  22. Change Direction • Some machines don’t change in either force or distance, they change the direction of the force. large input distance large output distance Small output force Small input force

  23. Mechanical Advantage • The number of times a machine increases a force exerted on it. • The ratio of output force to input force Mechanical Advantage = output force input force

  24. What happens when you increase Force? When the output force is greater than the input force - mechanical advantage > 1 YES 15N / 10N = 1.5 Greater

  25. What happens when distance increases? • When a machine increases distance, the output force (machine’s force) is less than the input force (your force). • Mechanical advantage is < 1

  26. What happens when direction changes? • Input force = output force • Mechanical advantage is 1. The larger the mechanical advantage, the easier a machine makes your work.

  27. What is efficiency? • The machine’s (output) work is always less than your (input) work because the machine has to overcome the force of friction. • The less work a machine has to do to overcome friction, the more efficient it is.

  28. To calculate efficiency... Output work X 100% Input work

  29. Lesson 3 Inclined Planes and Levers

  30. Simple Machines: Inclined Planes - Flat sloped surface Wedge - device that is thick on one end and tapers to a thin edge at the other Screw - be thought of as an inclined plane wrapped around a cylinder.

  31. Levers: • Rigid bar that is free to pivot, or rotate on a fixed point. • That fixed point is called a fulcrum • Types of levers are classified according to the location of the fulcrum relative to the input and output forces.

  32. Types of Levers: 1st Class

  33. Types of Levers: 2nd Class

  34. Types of Levers: 3rd Class

  35. More Examples of Levers:

  36. Lesson 4 Putting Machines Together

  37. PULLEY Systems Simple Machine made of a grooved wheel with a cable or rope wrapped around it.

  38. Types of Pulleys: Fixed Changes the direction of the force but not the amount applied:

  39. Types of Pulleys: Movable Decreases the amount of input force needed. It doesn’t change the direction of the force.

  40. Type of Pulleys: Block and Tackle A pulley system make up of fixed and movable pulleys.

  41. Wheel and Axle Two connected objects that rotate about a common axis.

More Related