Work and simple machines


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Work and simple machines

  1. 1. Work and machines Making jobs easier
  2. 2. Work <ul><li>Work is done on an object when a force is exerted on an object that causes the object to move some distance. </li></ul><ul><ul><li>No work without motion </li></ul></ul><ul><ul><li>No work without force in the same direction </li></ul></ul>
  3. 3. Motion and force <ul><li>Person does not work on weights – weights do not move </li></ul><ul><li>Person does work on weights – weights moved </li></ul>Summer Olympics 2000 Sydney Australia By Lou Jones Force on weights Force on weights
  4. 4. Direction and force <ul><li>Horse does not work on the rider – force not in same direction </li></ul><ul><li>Horse does work on the cart - force and motion in the same direction </li></ul>Force on person motion motion Force on cart
  5. 5. Calculating work <ul><li>Work = Force X Distance </li></ul><ul><ul><li>Force units = Newton, N </li></ul></ul><ul><ul><li>Distance units = meter, m </li></ul></ul><ul><ul><li>Work units = Joule, J </li></ul></ul><ul><ul><ul><li>J = N*m </li></ul></ul></ul>
  6. 6. Making work easier <ul><li>Machines </li></ul><ul><ul><li>Change the amount of force you exert </li></ul></ul><ul><ul><li>Change the distance over which you exert force </li></ul></ul><ul><ul><li>Change the direction in which you exert force </li></ul></ul><ul><ul><li>Do change the amount of work done </li></ul></ul>NOT
  7. 7. Total work does not change <ul><li>Work = Force X Distance </li></ul><ul><ul><li>If a machine allows you to apply a smaller force the distance will increase </li></ul></ul><ul><ul><li>If a machine reduces the distance the force will increase </li></ul></ul><ul><ul><li>If a machine allows you to apply a force in a different direction it doesn’t change how much force you have to apply or how far you move it </li></ul></ul>
  8. 8. Mechanical advantage <ul><li>The number of times a force exerted on a machine is multiplied by the machine </li></ul><ul><li>Mechanical ad. = Output force </li></ul><ul><li>Input force </li></ul><ul><li>If M.A. > 1 machine increases force needed but distance decreases </li></ul><ul><li>If M.A. < 1 machine reduces force needed but distance increases </li></ul>
  9. 9. Efficiency <ul><li>Efficiency compares the output work to the input work (%) </li></ul><ul><ul><li>Cannot be greater than 100% </li></ul></ul><ul><li>Efficiency usually < 100% </li></ul><ul><ul><li>Friction </li></ul></ul>
  10. 10. Types of simple machines <ul><li>Inclined plane </li></ul><ul><li>Wedge </li></ul><ul><li>Screw </li></ul><ul><li>Lever </li></ul><ul><li>Wheel and axle </li></ul><ul><li>pulley </li></ul>Image taken from:
  11. 11. Levers <ul><li>A lever is a simple machine that consists of a bar that pivots at a set point, called a fulcrum. </li></ul><ul><li>There are 3 classes of levers, which are based on where the input force, output force, and fulcrum are placed in relation to the load. </li></ul>
  12. 12. Lever simple/img/lever.gif
  13. 13. Types of machines – simple & compound. <ul><li>Simple machines do work with one movement. There are 6 simple machines. </li></ul><ul><li>A compound machine is made of 2 or more simple machines. </li></ul>
  14. 14. The 3 types of Levers <ul><li>First class lever: the fulcrum (fixed point) is between the input force and the load. </li></ul>
  15. 15. Second class lever. <ul><li>Second class ever: the load is between the fulcrum and the input force. </li></ul>
  16. 16. Third class lever. <ul><li>Third class lever: the input force is between the fulcrum and the load. </li></ul>
  17. 17. Inclined plane simple/img/plane.gif
  18. 18. Inclined plane <ul><li>An inclined plane is a slanted surface used to raise an object. </li></ul><ul><li>Work is made easier because the effort force moves over a greater distance. </li></ul><ul><li>Mechanical advantage is equal to the length of the plane divided by its height. </li></ul>
  19. 19. Wedge simple/img/wedge.gif
  20. 20. Wedge <ul><li>A moving inclined plane. </li></ul><ul><li>Force is multiplied since it is applied to a wide area and exerted over a small area. </li></ul><ul><li>The “sharper” the wedge the greater the mechanical advantage. </li></ul>
  21. 21. Screw simple/img/screw.gif
  22. 22. A screw <ul><li>An inclined plane wrapped around a cylinder. </li></ul><ul><li>It multiplies effort force by acting through a long effort distance. </li></ul><ul><li>The closer the threads on a screw, the greater the mechanical advantage. </li></ul>
  23. 23. Pulley simple/img/pulley.gif                                                         
  24. 24. Pulley <ul><li>A belt, rope, or chain wrapped around a wheel. </li></ul><ul><li>There are three main types of pulleys: fixed, movable, and block and tackle pulley system. </li></ul>
  25. 25. Fixed Pulley <ul><li>Does not multiply force. </li></ul><ul><li>Changes the direction of the effort force. </li></ul><ul><li>Mechanical advantage is equal to one. </li></ul>
  26. 26. Movable pulley <ul><li>Multiplies effort force but cannot change the direction of the effort force. </li></ul><ul><li>The mechanical advantage is the effort distance divided by the resistance distance. </li></ul>
  27. 27. Pulley system <ul><li>A combination of fixed and movable pulleys. </li></ul><ul><li>A mechanical advantage is equal to the number of supporting ropes. </li></ul>
  28. 28. Wheel and axle simple/img/wheel.gif
  29. 29. Wheel and axel <ul><li>A lever that rotates in a circle around an axel. </li></ul><ul><li>Two wheels of different sizes connected – the axel being the smaller wheel. </li></ul><ul><li>Effort force to the wheel is multiplied at the axel. </li></ul>
  30. 30. Additional information <ul><li>Do not rely on just this study guide. Some test and quiz questions will come from the book as well. </li></ul>