1. Machines -
Work
Power
Energy

2. Objectives Define work Explain how work and energy are related.
Calculate work and power
CLE Demonstrate the relationships among work, power, and machines.

3. A. Work Makes Something Move
1. Force is a push or a pull.
2. For work to be done, a force must make something move.
3. Work is the transfer of energy that occurs when a force makes an object move.

4. B. Doing work 1. For work to occur an object must move.
2. The motion of the object must be in the same direction as the applied force.

5. Doing work
When you lift a stack of books, your arms apply a force upward and the books move upward. Because the force and distance are in the same direction, your arms have done work on the books.

6. C. Force and Direction of Motion
Work
C. Force and Direction of Motion
When you carry books while walking, you might think that your arms are doing work.
However, the force exerted by your arms does NO work on the books.
The force exerted by your arms on the books is upward, but the books are moving horizontally.

7. 1. When work is done, a transfer of energy always occurs.
D. Work and Energy
1. When work is done, a transfer of energy always occurs.
2.This is easy to understand when you think about how you feel after carrying a heavy box up a flight of stairs.
3.Energy is the ability to do work.

8. Work
Work and Energy
4. Energy is transferred from the object that is always doing work to the object on which the work is done.

9. 1. The amount of work done depends on: the amount of force exerted
E. Calculating Work
1. The amount of work done depends on:
the amount of force exerted
the distance over which the force is applied.

10. E. Calculating Work W = F × d
2. When a force is exerted and an object moves in the direction of the force, the amount of work done can be calculated as follows:
Work = force (in newtons) x distance
W = F × d

11. W = F × d Calculating Work work = force x distance force = Newtons
w = f x d,
f = w/d,
d = w/f
Work = Joules
W = F × d
Calculating Wor

12. Calculating Work 3. Work, like energy, is measured in joules.
4. Joule - amount of work done when a force of one Newton acts through a distance of one meter)

13. F. Calculating Power 1.Power is the amount of work done in one second.
2. It is a rate - the rate at which work is done.

14. Work
Calculating Power
3. To calculate power, divide the work done by the time that is required to do the work.

15. Calculating Power
4. The SI unit for power is the watts (W). One watt equals one joule of work done in one second.
W = 1 kilowatt (kW)
6. Because the watt is a small unit, power often is expressed in kilowatts.

16. C. Power Power rate at which work is done measured in watts (W)
P: power (W)
W: work (J)
t: time (s)

17. C. Power P W t F = 450 N P = W ÷ t d = 1.0 m W = F·d t = 3.0 s
A figure skater lifts his partner, who weighs 450 N, 1.0 m in 3.0 s. How much power is required? P W t
GIVEN:
F = 450 N
d = 1.0 m
t = 3.0 s
WORK:
P = W ÷ t
W = F·d
W = (450 N)(1.0 m) = 450 J
P = 450 J ÷ 3.0 s
P = 150 W

18. G. Work
1. Since work and energy are related, power also can be calculated:
power = energy / time
2. Just as power is the rate at which work is done, power is also the rate at which energy is transferred.

19. Work
H. Power and Energy
When energy is transferred, the power involved can be calculated by dividing the energy transferred by the time needed for the transfer to occur.

20. Section Check 1
Question 1
__________ is the transfer of energy that occurs when a force makes an object move.
A. Conversion
B. Energization
C. Power
D. Work

21. Section Check
Answer
The answer is D. In order for work to be done, the applied force must make the object move in the same direction as the applied force.

22. The amount of work done depends on what two things?
Section Check
Question 2
The amount of work done depends on what two things?
Answer
The amount of work done depends on the amount of force exerted and the distance over which the force is applied.

23. Which of the following equations can be used to calculate power?
Section Check
Question 3
Which of the following equations can be used to calculate power?
A. w = f/d
B. p =w/t
C. t = w/p
D. p = t/w

24. Section Check
Answer
The answer is B. This is a rearrangement of the equation for calculating power, p = w/t.

25. How are work and energy related?
Energy is transferred from an object doing work to an object being worked on.

26. CLE 3202.4.3 Demonstrate the relationships among work, power, and machines.
Objective: Define work.
Objective: Explain how work and energy are related.
Objective: Calculate work and power.

27. Objectives Explain how work and energy are related.
Calculate work and power
CLE Demonstrate the relationships among work, power, and machines.