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Bellwork: What do you think are the differences between work and power?

Work and Power

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Page 1: Work and Power

Bellwork: What do you think are the differences between

work and power?

Page 3: Work and Power

What is work? Work- A force acting through a distance.

The distance that the object moves must be in the same direction as the force applied to the object.

Lifting Force

Movement Distance

What force is having to be overcome by the lifting force?

Gravity-Weight!

Weight

Page 4: Work and Power

Work Work- A force acting through a distance.

The distance that the object moves must be in the same direction as the force applied to the object.

Pushing Force

Distance Moved

What force is having to be overcome by the pushing force?

Friction!

Page 5: Work and Power

Lifting Force

Movement Distance

Work is not done every time a force is applied. Work is done only when a force moves an

object in the same direction as the applied force.

Is the man doing work when he lifts the box?

Yes.

Is the man doing work when he holds the box?

No! Is the man doing work if he carries the box?

No!(But he IS applying a force) (But he IS applying a force)

Page 6: Work and Power

WorkThink about pushing on wall that does not

move. A force is applied but the wall has not moved a distance.

Is work done?

Only when an object moves No!

But I did expend energy applying a force!

Page 7: Work and Power

Calculating Work Work = force (N) x distance (m)or Displacement

W = F x D The unit for work is a Joule (J). If you lifted an object weighing 1N through a

distance of 1m, you did 1 Joule of work:

W = FD = 1N x 1m = 1 J

A Newton is about ¼ of a pound.

Is a Joule of work…very much work? No!

Page 8: Work and Power

Calculating Work If you lifted an object weighing 200 N through a

distance of 0.5m, how much work would you do?

Work = force x distance = 200 N x 0.5m = 100 J.

Page 9: Work and Power

What is power? Power is the rate at which work is done, or the

amount of work per unit of time.

Two men can move a lot of sand using shovels…

Page 10: Work and Power

Power Power is the rate at which work is done, or the

amount of work per unit of time.

Two men can move a lot of sand using shovels…

…but a front-end loader can do it in less time…

…because the front-end loader has more POWER.

Page 11: Work and Power

Power Power is the rate at which work is

done , or the amount of work per unit of time.

Power = work / time or

Power = force x distance / time

Because work = force x distance

Page 12: Work and Power

Power The unit for power is watt (W). One watt

is equal to 1 joule per second (1 J/sec).

Large quantities of power are measured in kilowatts (kW).

One kilowatt equals _____ watts. One million watts is a megawatt

1000

Page 13: Work and Power

Summary

Create a Venn Diagram comparing work and power