1. Work, power, and machines
CHAPTER 14
Work, power, and machines

2. SECTION 14.1

3. I. WORK AND POWER A. WHAT IS WORK? Work requires motion
Work is a product of force and distance
Work depends on direction

4. Work depends on direction

5. B. CALCULATING WORK Equation: Work = Force x Distance W= F x d
Work is measured in Joules (SI unit)
1(Newton)(meters)= 1(Joule)
Work - Joules (J)
Force – Newton's (N)
Distance – Meters (m)
Power – Watts (W)
Time – Seconds (s)

6. B. CALCULATING WORK Work = force x distance Work = 1600N x 2.0m
Work = 3200(N)(m) = 3200J
Imagine Isaac lifting Joseph into the air repeatedly. How much WORK does he do with each lift? He lifts Joseph 2.0m and exerts an average force of 190 N?
W = ________ x________ = _________
W= 190N x 2.0 m
W = 380 N x m = 380J

7. C. What is Power?
1.Power – a quantity that measures the rate at which work is done
Power = Work /Time or P = W/T
2. Power is measured in Watts (W)
3. Watts is the amount of power that is required to do 1 Joule of work in 1 second

8. C. Calculating Power
How much power is used if a force of 25 Newton's is used to push a box a distance of 10 meters in 5 seconds. How much power is used?
P= work Work isn’t given so what
time do you do?
Find work first (W= F x d) W= 25N x 10m= 250
Work 250J = 50Watts
time 5s

9. D. James Watt and Horsepower
Besides a watt, another common unit of power is the horsepower (hp)
1 (hp) = 746 watts

10. Section 14.2
Work and Machines

11. A. Machines Do Work A machine is a device that changes a force.
Machines make work easier
They change the size of force needed, the direction of a force or the distance over which a force acts.

12. B. Work Input and Work Output
The force you exert on a machine is called the input force.
C. Work Output of a machine
The force that is exerted by a machine is the output force.

13. Mechanical Advantage and Efficiency
SECTION 14.3
Mechanical Advantage and Efficiency

14. A. Mechanical Advantage
The number of times that the machine increases an input force.

15. 1. Actual Mechanical Advantage
AMA- equals the ratio of the output force to the input force
2. Ideal Mechanical Advantage (IMA) is mechanical advantage in the absence of friction

16. B. Calculating mechanical advantage
MA = output /input

17. Simple Machines
1. Simple Machines – one of six basic types of machines of which all other machines are composed

18. The Lever Family
Simple lever
Wheel and Axle
Pulley

19. Levers are divided into 3 different classes
1st class – have a fulcrum in the middle of an arm. Input force acts on one end and the other end applies an output force

20. Second Class Lever
The fulcrum is at one end of the arm and the input force is applied at the other end

21. Third class lever
Multiply distance rather than force. As a result, they have a mechanical advantage of less than 1. ( The human body has many)

22. Pulleys
Pulleys are modified levers

23. The Inclined Plane Family
Multiply and redirect force
Ex. Apply force to push an object up a ramp, The ramp redirects force to lift the object upward

24. Inclined Planes
1. Wedge – turns downward force into forces directed out to the sides

25. Inclined Planes
2. Screw- an inclined plane wrapped around a cylinder

26. Inclined Planes
3. Inclined plane- changes both magnitude and the direction of force

27. Compound Machines
Combines two or more simple machines

28. I. Energy and Work Energy measured in joules
Transfer energy from doing work
Ex. Slingshot