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ENERGY, WORK AND SIMPLE MACHINES     CHAPTER 10
ENERGY AND WORK• How do we define the relationship between work  and energy?• How can we calculate work done?• How do we c...
WORK EQUATION•
WORK EQUATION•
WORK EQUATION• Right side is Fd• F = force (in Newtons)• d = distance (in meters)• We define:• W = Fd• Work = forces times...
WORK ENERGY THEOREM•
EXAMPLE• A 105 g hockey puck  is sliding across the  ice. A player exerts a  constant 4.50 newton  force over a distance  ...
LIFTING A BOOK• When is the work positive?• When is the work negative?• When is the work zero?
WORK AGAINST GRAVITY• W = Fd• The work of lifting something is equal to the weight  of the object times the distance lifte...
WORK• Since work equals the change in KE, the unit is the  same• Work is measured in joules• One joule happens when a forc...
WORK• What if our force is not applied in a straight line?• Will it be as effective?• How do we account for this?
WORK• W = Fdcosɵ• ɵ is between the  force and the  direction of  displacement• If he pushes the car  10.0 m, how much  wor...
WHAT TO INCLUDE IN WORK• Which direction do  the normal force  and gravity point?• ɵ is …• What about  friction?
EXAMPLE• A sailor pulls a boat  a distance of 30.0 m  along a dock using  a rope that makes  a 25.0° angle with  the horiz...
TRIG REFRESHER• SOH-CAH-TOA
WORK AGAINST GRAVITY• Pushing up a ramp,  walking up stairs• What do we use for  d?
HOMEWORK• Page 287, # 1 – 3• Page 291, # 4 - 8
GRAPHICAL METHOD• Area under force vs  displacement curve  is work• How much work?
GRAPHICAL METHOD• Force exerted by a  spring• Work =• Area of a  trapezoid=• ½ h (b1 + b2)
MULTIPLE FORCES• If several forces are exerted on a system, calculate  the work done by each force, then add the results
POWER•
POWER• Three student going  up stairs• If they started at the  same time…• How does their work  compare?• How does their p...
POWER• On a ten-speed  bike, there is a  combination of  force and speed  that will produce  the maximum  power
EXAMPLE• An electric motor lifts an elevator 9.00 m in 15.0 s by  exerting an upward force of 1.20 x 104 N. What  power do...
HOMEWORK• Page 264, # 9 – 14• Page 265, # 15 - 21
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General/Notes 10.1

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General/Notes 10.1

  1. 1. ENERGY, WORK AND SIMPLE MACHINES CHAPTER 10
  2. 2. ENERGY AND WORK• How do we define the relationship between work and energy?• How can we calculate work done?• How do we calculate power used?
  3. 3. WORK EQUATION•
  4. 4. WORK EQUATION•
  5. 5. WORK EQUATION• Right side is Fd• F = force (in Newtons)• d = distance (in meters)• We define:• W = Fd• Work = forces times distance
  6. 6. WORK ENERGY THEOREM•
  7. 7. EXAMPLE• A 105 g hockey puck is sliding across the ice. A player exerts a constant 4.50 newton force over a distance of 0.150 m. How much work does the player do on the puck? What is the change in energy?
  8. 8. LIFTING A BOOK• When is the work positive?• When is the work negative?• When is the work zero?
  9. 9. WORK AGAINST GRAVITY• W = Fd• The work of lifting something is equal to the weight of the object times the distance lifted• Weight =• So W =
  10. 10. WORK• Since work equals the change in KE, the unit is the same• Work is measured in joules• One joule happens when a force of 1 N acts for 1 m• An apple is approximately a newton, so lifting an apple 1 meter is about 1 Joule of work
  11. 11. WORK• What if our force is not applied in a straight line?• Will it be as effective?• How do we account for this?
  12. 12. WORK• W = Fdcosɵ• ɵ is between the force and the direction of displacement• If he pushes the car 10.0 m, how much work did the man do?
  13. 13. WHAT TO INCLUDE IN WORK• Which direction do the normal force and gravity point?• ɵ is …• What about friction?
  14. 14. EXAMPLE• A sailor pulls a boat a distance of 30.0 m along a dock using a rope that makes a 25.0° angle with the horizontal. How much work does the sailor do on the boat if he exerts a force of 255 N on the rope?
  15. 15. TRIG REFRESHER• SOH-CAH-TOA
  16. 16. WORK AGAINST GRAVITY• Pushing up a ramp, walking up stairs• What do we use for d?
  17. 17. HOMEWORK• Page 287, # 1 – 3• Page 291, # 4 - 8
  18. 18. GRAPHICAL METHOD• Area under force vs displacement curve is work• How much work?
  19. 19. GRAPHICAL METHOD• Force exerted by a spring• Work =• Area of a trapezoid=• ½ h (b1 + b2)
  20. 20. MULTIPLE FORCES• If several forces are exerted on a system, calculate the work done by each force, then add the results
  21. 21. POWER•
  22. 22. POWER• Three student going up stairs• If they started at the same time…• How does their work compare?• How does their power compare?
  23. 23. POWER• On a ten-speed bike, there is a combination of force and speed that will produce the maximum power
  24. 24. EXAMPLE• An electric motor lifts an elevator 9.00 m in 15.0 s by exerting an upward force of 1.20 x 104 N. What power does the motor produce in kW?
  25. 25. HOMEWORK• Page 264, # 9 – 14• Page 265, # 15 - 21

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