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Work, Power, and Machines

Work, Power, and Machines. 9.1. A quantity that measures the effects of a force acting over a distance Work = force x distance W = Fd. Work. Work is measured in: N m Joules (J). Work. A crane uses an average force of 5200 N to lift a girder 25 m. How much work does the crane do?.

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Work, Power, and Machines

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  1. Work, Power, and Machines 9.1

  2. A quantity that measures the effects of a force acting over a distance • Work = force x distance • W = Fd Work

  3. Work is measured in: • Nm • Joules (J) Work

  4. A crane uses an average force of 5200 N to lift a girder 25 m. How much work does the crane do? Work Example

  5. Work = Fd • Work = (5200 N)(25m) • Work = 130000 N  m = 130000 J Work Example

  6. A quantity that measures the rate at which work is done • Power = work/time • P = W/t Power

  7. Watts (W) is the SI unit for power • 1 W = 1 J/s Power

  8. While rowing in a race, John uses 19.8 N to travel 200.0 meters in 60.0 s. What is his power output in Watts? Power Example

  9. Work = Fd • Work = 19.8 N x 200.0 m= 3960 J • Power = W/t • Power = 3960 J/60.0 s • Power = 66.0 W Power Example

  10. Help us do work by redistributing the force that we put into them • They do not change the amount of work Machines

  11. Change the direction of an input force (ex car jack) Machines

  12. Increase an output force by changing the distance over which the force is applied (ex ramp) • Multiplying forces Machines

  13. A quantity that measures how much a machine multiples force or distance. Mechanical Advantage

  14. Inputdistance Mech. Adv = Output Distance Mechanical Advantage Output Force Mech. Adv. = Input Force

  15. Calculate the mechanical advantage of a ramp that is 6.0 m long and 1.5 m high. Mech. Adv. example

  16. Input = 6.0 m • Output = 1.5 m • Mech. Adv.=6.0m/1.5m • Mech. Adv. = 4.0 Mech. Adv. Example

  17. Energy 9.3-9.4

  18. Energy is the ability to do work • whenever work is done, energy is transformed or transferred to another system. Energy and Work

  19. Energy is measured in: • Joules (J) • Energy can only be observed when work is being done on an object Energy

  20. the stored energy resulting from the relative positions of objects in a system Potential Energy PE

  21. PE of any stretched elastic material is called Elastic PE • ex. a rubber band, bungee cord, clock spring PotentialEnergy PE

  22. energy that could potentially do work on an object due to the forces of gravity. Gravitational PE

  23. depends both on the mass of the object and the distance between them (height) Gravitational PE

  24. grav. PE= mass x gravity x height PE = mgh or PE = wh Gravitational PE Equation

  25. A 65 kg rock climber ascends a cliff. What is the climber’s gravitational PE at a point 35 m above the base of the cliff? PE Example

  26. PE = mgh • PE=(65kg)(9.8m/s2)(35m) • PE = 2.2 x 104 J • PE = 22000 J PE Example

  27. the energy of a moving object due to its motion. • depends on an objects mass and speed. Kinetic Energy

  28. What influences energy more: speed or mass? ex. Car crashes • Speed does Kinetic Energy

  29. KE=1/2 x mass x speed squared KE = ½ mv2 Kinetic Energy Equation

  30. What is the kinetic energy of a 44 kg cheetah running at 31 m/s? KE Example

  31. KE = ½ mv2 • KE= ½(44kg)(31m/s)2 • KE=2.1 x 104 J • KE = 21000 J KE Example

  32. the sum of the KE and the PE of large-scale objects in a system • work being done Mechanical Energy

  33. Energy that lies at the level of atoms and does not affect motion on a large scale. Nonmechanical Energy

  34. Atoms have KE, because they are constantly in motion. • KE  particles heat up • KE  particles cool down Atoms

  35. during reactions stored energy (called chemical energy)is released • So PE is converted to KE Chemical Reactions

  36. nuclear fusion • nuclear fission • Electricity • Light Other Forms

  37. Energy Transformations 9.4

  38. Energy is neither created nor destroyed • Energy is transferred Conservation of Energy

  39. PE becomes KE • car going down a hill on a roller coaster Energy Transformation

  40. KE can become PE • car going up a hill KE starts converting to PE Energy Transformation

  41. http://www.funderstanding.com/k12/coaster/ Physics of roller coasters

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