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# Work and Power - PowerPoint PPT Presentation

Work and Power. Chapter 14. Work and Power. 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

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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

• 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

• 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

• 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

• 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