1. Work, Simple Machines, and Mechanical Advantage

2. Work
In scientific terms, work is done when a force causes an object to move in the direction of the force.
W = F x D: Work is calculated as force times distance. The unit of work is the newton-meter, or joule.
The object must move in the direction of the force for work to be done.

3. Work or Not?

4. YES, as long as the box moves in the direction of the force.
Work or Not?
YES, as long as the box moves in the direction of the force.

5. Work or Not?

6. Work or Not?
NO – work was done on the backpack when it was first picked up, but is not being done now.

7. Work or Not?

8. YES! The bag is moving up as it is being lifted up.
Work or Not?
YES! The bag is moving up as it is being lifted up.

9. Work or Not?
NO, work is not being done on the bag since the applied force is not in the direction of movement.

10. Remember: Work is a transfer of energy
You can apply a force but not do work
You can set an object in motion, and it may keep moving even though you are no longer doing work

11. Question: Work is being done when:
you apply a force to an object.
an object is moving after you applied a force to it.
you exert a force that moves an object in the direction of the force.
you do something that is difficult.

12. Answer: Work is being done when:
you apply a force to an object.
an object is moving after you applied a force to it.
you exert a force that moves an object in the direction of the force.
you do something that is difficult.

13. Power Power is a measure of how fast work is done.
W/t = P: Power is calculated as work divided by time. The unit of power is the joule per second, or watt.

14. What can a machine do? A simple machine does NOT reduce work
A machine makes work easier by changing the size or direction (or both) of a force.
A machine can increase force or distance, but not both.

15. Changes direction of the force

16. Changes the size of the force

17. Trades force for distance

18. Six Simple Machines Inclined Plane Wedge Screw Lever Pulley
Wheel & Axle

19. Terminology - Synonyms
Where your hands are
Where the load is
Effort
Input
Output DISTANCE
Load
Output
Resistance
Input DISTANCE

20. Mechanical Advantage is…
A multiplier that shows how much a machine is amplifying a force

21. Mechanical Advantage

22. Mechanical Advantage
Resistance Force = Input Distance = Effort Distance = Output Force
Effort Force = Output Distance = Resistance Distance
= Input Force

23. Other forms of the MA formula:

24. Mechanical Efficiency
Mechanical Efficiency = Work Output X 100
Work Input

25. Inclined Plane Reduces force, but increases distance
The mechanical advantage of an inclined plane is length divided by height.
Wedges and screws are types of inclined planes.

27. MA = L/H

28. Wedge A wedge generates outward forces
A wedge is a type of inclined plane. Its mechanical advantage is its length divided by its greatest thickness.

29. Screw A screw is an inclined plane wrapped around a cylinder
Uses a small force over a longer distance
The closer the threads, the lower the force required

30. Levers – Three Classes Can change direction & size of force
In a first-class lever, the fulcrum is between the force and the load.
In a second-class lever, the load is between the force and the fulcrum.
In a third-class lever, the force is between the fulcrum and the load.

31. First Class
Second Class
Third Class

32. First Class Lever Change direction & maybe force

33. Second Class Lever Change force, but not direction

34. Third Class Lever Don’t change direction, output < input

35. Pulleys Change direction and may change input force
Types of pulleys include fixed pulleys, movable pulleys, and block and tackles.

37. Wheel and Axle
The mechanical advantage of a wheel and axle is the radius of the wheel divided by the radius of the axle.

38. Compound Machines
Compound machines consist of two or more simple machines.
Compound machines have low mechanical efficiencies because they have more moving parts and therefore more friction to overcome.

39. Question 1 Which of the following simple machines is a wedge?
A. Wheelbarrow
B. Doorknob
C. Ax
D. Truck ramp

40. Answer
Which of the following simple machines is an example of a wedge?
A. Wheelbarrow
B. Doorknob
C. Ax
D. Truck ramp

41. Question 2 What is the pivot point of a lever called? A. Load
B. Fulcrum
C. Wedge
D. Effort

42. Answer What is the pivot point of a lever called? A. Load B. Fulcrum
C. Wedge
D. Effort

43. Question 3
A student pushes on a lever with a force of 40N. The 150N load does not move. Which of the following is true?
A. Input force is 40 N and work done is 0 J.
B. Input force is 40 N and work done is 600 J.
C. Output force is 40 N and work done is 150J.
D. Output force is 150N and work done is 40J.

44. Answer
A student pushes on a lever with a force of 40N. The 150N load does not move. Which of the following is true?
A. Input force is 40 N and work done is 0 J.
B. Input force is 40 N and work done is 600 J.
C. Output force is 40 N and work done is 150J.
D. Output force is 150N and work done is 40J.