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Work and Power

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Work and Power

Chapter 14

- Work in physics is not the same as the everyday meaning of work…
- Work- the product of force and distance
-the transfer of energy

- Work is done when a force is exerted on an object and that object moves
- Work requires motion
- For a force to do work on an object, some of the force must act in the same direction as the object moves. If there is no movement, no work is done

- Work is done when a force is exerted on an object and that object moves

- Work- the product of force and distance

- Work
- Work depends on Direction
- Any part of a force that does not act in the direction of motion does no work on an object
- See figure 2-B

- Any part of a force that does not act in the direction of motion does no work on an object

- Work depends on Direction

- Calculating Work
- Work = Force x Distance
- Force in newtons (N)
- Distance in meters (m)
- Work in joules (J)

- Sample Problem: A weight-lifter applies force to a 1600 N barbell, to lift it over his head (a height of 2.0 m). How much work is done by the weight-lifter?
- W = F x D

- Work = Force x Distance

- Power- is the rate of doing work
- Doing work at a faster rate requires more power. To increase power, you can increase the amount of work done in a give time, or you can do a given amount of work in less time.

- Calculating Power
- Power = Work/Time
- Work in joules (J)
- Time in seconds (s)
- Power in watts (W)
- One watt is equal to one joule per second

- Sample Problem: When you lift a box, work is done (1340 J). It takes you 1.8 seconds to lift the box. How much power is done?
- P = W/t

- Power = Work/Time

- Sample Problem:
- You exert a vertical force of 88 N to lift a box to a height of 1.5 m in a time of 2.3 seconds. How much power is used to lift the box?
- W = FxD & P = W/t

- You exert a vertical force of 88 N to lift a box to a height of 1.5 m in a time of 2.3 seconds. How much power is used to lift the box?