Work and Power notes

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

2. Title of Cornell Notes
 Work and Power

3. 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

4. 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!

5. 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)

6. Work
Think 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!

7. 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!

8. 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.

9. 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…

10. 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.

11. 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

12. 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

13. Summary
 Create a Venn Diagram comparing work
and power