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Work, Power and Machines

Work, Power and Machines. Chapter 14. What is work?. Work is the product of force and distance Work is done when a force acts on an object in the direction the object moves Key point: Force must act in the same direction of the movement. If no movement, no work is done. Work.

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Work, Power and Machines

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  1. Work, Power and Machines Chapter 14

  2. What is work? • Work is the product of force and distance • Work is done when a force acts on an object in the direction the object moves • Key point: Force must act in the same direction of the movement. If no movement, no work is done.

  3. Work • The amount of work done on an object depends on the direction of the force and the direction of the movement. • Key Point: Any part of the force that does not act in the direction of the motion does no work on the object

  4. Calculating Work • Work = force x distance • W = Fd • SI unit for work = Joule

  5. Examples • How much work is done if 50 N is applied to move a box 3 m? • If 36 J of work is done for 5 m, how much force is applied? • While lifting a book 1.5 m straight up you exert a force of 150 N. How much work is done?

  6. Power • Is the rate of doing work (how fast) • Key Point: Doing work at a faster rate requires more power. • To increase Power you can • Increase the work done 2. Do the work in less time

  7. Equation • Power = work/time • Hint – you may have to calculate work first • So Power = (fxd)/t

  8. Examples • You exert a vertical force of 72 N to lift a box to a height of 3.5 m in a time of 3.0 s. How much power is used to lift the box? • When lifting a box 1.5 m you exert a force of 350 N for 2.7 s. How much power is required to do this?

  9. Machines • Device that changes a force • Make work easier • Change the size, the direction, or the distance over which the force acts. • Because of friction, the work done by a machine is always less than the work done on the machine.

  10. Six types of Simple Machines • Lever -- a rigid bar free to move around a fixed point ex. Wheel barrel and broom • Wheel and Axle -- 2 disks or cylinders, each with different radius ex. Screwdriver and steering wheel

  11. Inclined Plane --a slanted surface along which a force moves an object to a different elevation ex. Sloping roads and ramps • Wedge -- V shaped --two sides are inclined planes ex. Knives and sledge hammer

  12. Screws --inclined plane wrapped around a cylinder • Pulleys --rope that fits into the groove of a wheel ex. elevators

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