Thermal sys physics chpt10


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Thermal sys physics chpt10

  1. 1. CPO Science<br />Foundations of Physics<br />Chapter 9<br />Unit 4, Chapter 10<br />
  2. 2. Unit 4: Energy and Momentum<br />Chapter 10 Work and Energy<br />10.1 Machines and Mechanical Advantage<br />10.2 Work<br />10.3 Energy and Conservation of Energy<br />
  3. 3. Chapter 10 Objectives<br />Calculate the mechanical advantage for a lever or rope and pulleys.<br />Calculate the work done in joules for situations involving force and distance.<br />Give examples of energy and transformation of energy from one form to another.<br />Calculate potential and kinetic energy.<br />Apply the law of energy conservation to systems involving potential and kinetic energy.<br />
  4. 4. Chapter 10 Vocabulary Terms<br /><ul><li>machine
  5. 5. energy
  6. 6. input force
  7. 7. output force
  8. 8. thermal energy
  9. 9. ramp
  10. 10. gear
  11. 11. screw
  12. 12. rope and pulleys
  13. 13. closed system
  14. 14. work
  15. 15. lever
  16. 16. friction
  17. 17. mechanical system
  18. 18. simple machine
  19. 19. potential energy
  20. 20. kinetic energy
  21. 21. radiant energy
  22. 22. nuclear energy
  23. 23. chemical energy
  24. 24. mechanical energy
  25. 25. mechanical advantage
  26. 26. joule
  27. 27. pressure
  28. 28. energy
  29. 29. conservation of energy
  30. 30. electrical energy
  31. 31. input output
  32. 32. input arm output
  33. 33. arm
  34. 34. fulcrum</li></li></ul><li>10.1 Machines and Mechanical Advantage<br />Key Question:<br />How do simple machines work?<br />*Students read Section 10.1 AFTER Investigation 10.1<br />
  35. 35. 10.1 Machines<br />The ability of humans to build buildings and move mountains began with our invention of machines.<br />In physics the term “simple machine” means a machine that uses only the forces directly applied and accomplishes its task with a single motion.<br />
  36. 36. 10.1 Machines<br />The best way to analyze what a machine does is to think about the machine in terms of input and output.<br />
  37. 37. 10.1 Mechanical Advantage<br />Mechanical advantage is the ratio of output force to input force.<br />For a typical automotive jack the mechanical advantage is 30 or more.<br />A force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)— enough to lift one corner of an automobile.<br />
  38. 38. 10.1 Mechanical Advantage<br />Output force (N)<br />MA = Fo<br /> Fi<br />Mechanical<br />advantage<br />Input force (N)<br />
  39. 39. 10.1 Mechanical Advantage of a Lever<br />Length of input arm <br />(m)<br />MAlever = Li<br /> Lo<br />Mechanical<br />advantage<br />Length of output arm<br />(m)<br />
  40. 40.
  41. 41. 10.1 Calculate position<br />Where should the fulcrum of a lever be placed so one person weighing 700 N can lift the edge of a stone block with a mass of 500 kg?<br /><ul><li>The lever is a steel bar three meters long.
  42. 42. Assume a person can produce an input force equal to their own weight.
  43. 43. Assume that the output force of the lever must equal half the weight of the block to lift one edge.</li></li></ul><li>
  44. 44. 10.1 Wheels, gears, and rotating machines<br />Axles and wheels provide advantages.<br />Friction occurs where the wheel and axle touch or where the wheel touches a surface.<br />Rolling motion creates less wearing away of material compared with two surfaces sliding over each other.<br /><ul><li>With gears the trade-off is made between torque and rotation speed.
  45. 45. An output gear will turn with more torque when it rotates slower than the input gear.</li></li></ul><li>10.1 Ramps and Screws<br />Ramps reduce input force by increasing the distance over which the input force needs to act.<br />A screw is a simple machine that turns rotating motion into linear motion. <br />A thread wraps around a screw at an angle, like the angle of a ramp.<br />
  46. 46. 10.2 Work<br />Key Question:<br />What are the consequences of multiplying forces in machines?<br />*Students read Section 10.2 AFTER Investigation 10.2<br />
  47. 47. 10.2 Work<br />In physics, work has a very specific meaning. <br />In physics, work represents a measurable change in a system, caused by a force.<br />
  48. 48. 10.2 Work<br />If you push a box with a force of one newton for a distance of one meter, you have done exactly one joule of work.<br />
  49. 49. 10.2 Work (force is parallel to distance)<br />Force (N)<br />W = F x d<br />Work (joules)<br />Distance (m)<br />
  50. 50. 10.2 Work (force at angle to distance)<br />Force (N)<br />W = Fd cos (q)<br />Work (joules)<br />Angle<br />Distance (m)<br />
  51. 51.
  52. 52. 10.2 Work done against gravity<br />Mass (g)<br />Height object raised (m)<br />W = mgh<br />Work (joules)<br />Gravity (m/sec2)<br />
  53. 53. 10.3 Why the path doesn't matter<br />
  54. 54. 10.3 Calculate work<br />A crane lifts a steel beam with a mass of 1,500 kg. <br />Calculate how much work is done against gravity if the beam is lifted 50 meters in the air. <br />How much time does it take to lift the beam if the motor of the crane can do 10,000 joules of work per second?<br />
  55. 55.
  56. 56. 10.3 Energy and Conservation of Energy<br />Energy is the ability to make things change.<br />A system that has energy has the ability to do work.<br />Energy is measured in the same units as work because energy is transferred during the action of work.<br />
  57. 57. 10.3 Forms of Energy<br />Mechanical energy is the energy possessed by an object due to its motion or its position.<br />Radiant energy includes light, microwaves, radio waves, x-rays, and other forms of electromagnetic waves.<br />Nuclear energy is released when heavy atoms in matter are split up or light atoms are put together.<br />The electrical energy we use is derived from other sources of energy.<br />
  58. 58.
  59. 59. 10.3 Potential Energy<br />Mass (kg)<br />Ep = mgh<br />Potential Energy<br /> (joules)<br />Height (m)<br />Acceleration<br />of gravity (m/sec2)<br />
  60. 60. 10.3 Potential Energy<br />A cart with a mass of 102 kg is pushed up a ramp. <br />The top of the ramp is 4 meters higher than the bottom. <br />How much potential energy is gained by the cart? <br />If an average student can do 50 joules of work each second, how much time does it take to get up the ramp?<br />
  61. 61. 10.3 Kinetic Energy<br />Energy of motion is called kinetic energy. <br />The kinetic energy of a moving object depends on two things: mass and speed.<br />Kinetic energy is proportional to mass.<br />
  62. 62. 10.3 Kinetic Energy<br />Mathematically, kinetic energy increases as the square of speed.<br />If the speed of an object doubles, its kinetic energy increases four times. (mass is constant)<br />
  63. 63. 10.3 Kinetic Energy<br />Mass (kg)<br />Speed (m/sec)<br />Ek = 1 mv2<br /> 2<br />Kinetic Energy <br />(joules)<br />
  64. 64. 10.3 Kinetic Energy<br />Kinetic energy becomes important in calculating braking distance.<br />
  65. 65. 10.3 Calculate Kinetic Energy<br />A car with a mass of 1,300 kg is going straight ahead at a speed of 30 m/sec (67 mph). <br />The brakes can supply a force of 9,500 N.<br />Calculate:<br />a) The kinetic energy of the car.<br />b) The distance it takes to stop.<br />
  66. 66. 10.3 Law of Conservation of Energy<br />As energy takes different forms and changes things by doing work, nature keeps perfect track of the total. <br />No new energy is created and no existing energy is destroyed.<br />
  67. 67. 10.3 Energy and Conservation of Energy<br />Key Question:<br />How is motion on a track related to energy?<br />*Students read Section 10.3 BEFORE Investigation 10.3<br />
  68. 68. Application: Hydroelectric Power<br />