1. Work and Power

2. 1. What is work?
In science, the definition of work is: using a force to move an object a distance
Both the force and the motion of the object are in the same direction.)

3. 2. Work or Not?
According to the scientific definition, what is work and what is not?
a teacher lecturing to her class
a mouse pushing a piece of cheese with its nose across the floor
No!
Yes!

6. 5. What’s work?
A scientist delivers a speech to an audience of his peers.
A body builder lifts 350 pounds above his head.
A mother carries her baby from room to room.
A father pushes a baby in a carriage.
A woman carries a 20 kg grocery bag to her car?

7. What’s work?
A scientist delivers a speech to an audience of his peers. No
A body builder lifts 350 pounds above his head. Yes
A mother carries her baby from room to room. No
A father pushes a baby in a carriage. Yes
A woman carries a 20 kg grocery bag to her car? No

8. 6. Formula for work Work = Force x Distance
The unit of force is Newtons
The unit of distance is meters
The unit of work is Newton-meters
One Newton-meter is equal to one joule
So, the unit of work is a joule

9. 7. The Joule
Named after British physicist James Prescott Joule.

10. 8. Let’s practice calculating work.
Work = Force x Distance
Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

11. W=FD Work = Force x Distance
Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules
(W = 20N x 10m)

13. 9. Power What do you think makes something powerful?
How quickly work is done.
Amount of work done per unit of time.
Formula:
POWER = WORK / TIME

14. The unit of power is the watt.

16. The watt A unit named after Scottish inventor James Watt.
Invented the steam engine.

17. Watts Used to measure power of light bulbs and small appliances
An electric bill is measured in kW/hrs.
1 kilowatt = 1000 W

18. Which is more powerful?

19. w w d P t F
2500J
W = 500N x 5m =
0.5 m
d = 2J / 4N =
P= 90 J / 20 s =
4.5 W
t= 20 J / 6 W =
3.33 s

20. Survey