1. Simple Machines and Mechanical Advantage

2. Remember Work?
Remember: Work = using a force to move an object some distance (in the same direction as the applied force.)
Formula for work Work = Force x Distance W = Fd
Unit of Work = Newton*meter = Joule

3. 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?

4. 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 km grocery bag to her car? No

5. Simple machines are tools used to make work easier.

6. Simple Machines
Simple machine = a device that helps make work easier to perform by accomplishing one or more of the following functions:
transferring a force from one place to another,
changing the direction of a force,
increasing the magnitude of a force, or
increasing the distance or speed of a force.

7. You have probably used some simple machines, but did not realize that they were actually called simple machines!

8. It would be hard to cut this wood without the saw!
Simple machines do not make less work; they just make it easier to do work.
It would be hard to cut this wood without the saw!

9. Simple Machines: Work input and output
Work input = amount of work done on (applied to) a machine.
Winput = Input force x input distance
Work output = amount of work done by a machine.
Woutput = Output force x output distance
For Ideal machines (no friction)
Wout = Win
Fout x Dout = Fin x Din
10N x 3m = 2N x 15m
15 m
3 m
10 N
Fin
Din
Dout

10. Mechanical Advantage Input force = force YOU apply (to machine)
Output force = force that the machine applies to the object/task (resistance).
(Actual ) Mechanical Advantage = the ratio of the output force divided by input force.
AMA = OUTPUT (Resistance/Load) Force INPUT (Effort) Force
If the output force >the input force, the machine has a mechanical advantage > 1.

11. Mechanical Advantage
If a machine increases an input force of 10 Newtons to an output force of 100 Newtons, the machine has a mechanical advantage (AMA) of [= 100 / 10].

12. Mechanical Advantage
For machines that increase DISTANCE instead of force, the (Ideal) Mechanical Advantage = ratio of output distance divided by input dist.
IMA = ____INPUT (Effort) Distance_______ OUTPUT (Resistance/Load) Distance
If a machine converts an input distance of 6 m to an output distance of 2 m, it has an IMA of 3 [= 6 / 2].

13. Mechanical Advantage
No machine can increase BOTH the magnitude and the distance of a force at the same time.

14. The 6 Simple Machines Screw Wedge Inclined Plane Pulley Wheel and Axle
Lever

15. Simple Machines The six simple machines are: Inclined Plane Screw
Wedge
Lever
Pulley
Wheel and Axle

16. 1. Inclined Plane Inclined plane = an even sloping surface.
makes it easier to move a weight from a lower to higher elevation.

17. 1. Inclined Plane
Mechanical Advantage of an inclined plane MA = __Length of the Slope__ Height of Inclined Plane
It produces a mechanical advantage (need less force to move object) by increasing the distance through which the force must move.

18. Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.
A B C

19. Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.
A B C

20. 2. Screw SCREW = The threads of a screw are a circular ramp
an inclined plane wrapped around a shaft or cylinder
allows the screw to move itself when rotated.

21. 2. Screw Mechanical Advantage of an screw
= Number of Turns in the Threads
Length of the Threads

22. 3. Wedge Wedge = 2 inclined planes joined back to back.
used to split things or as holding devices.

23. 3. Wedge Mechanical Advantage
Mechanical Advantage of a wedge MA = length of either slope (S) thickness (T) of the big end.
Ex: If the length of the slope is 10 cm & the thickness is 4 cm. Then, MA = 10 / 4 = 2.5
As with the inclined plane, MA (less force needed) is gained by the increase in distance (T  S). T S

24. A lever is used to push, pull, or lift things.
LEVER = a rigid bar (straight or curved) that moves about a fixed point (fulcrum).
A lever is used to push, pull, or lift things.

25. 4. Levers a lever has both an Effort (applied) force and a
Load (Resistance) force

26. The 3 Classes of Levers
The class of a lever is determined by the location of the effort force, load, and the fulcrum (pivot point).

27. Mechanical Advantage of a lever = Output force [Load/Resistance] Input force [Effort] or = Length of the Effort (Input) arm Length of the Resistance (Load) arm

28. First Class Lever
the fulcrum is in the middle and the load and effort are on opposite sides.
Common examples include crowbars, scissors, pliers, tin snips and seesaws.
A first-class lever always changes the direction of force (I.e. downward effort force = upward movement of Load( resistance).

29. Fulcrum is between EF (effort) and RF (load) Effort moves farther than Resistance. Multiplies EF and changes its direction

30. Second Class Lever
the fulcrum is at the end, with the load in the middle
Examples include nut crackers, wheel barrows, doors, and bottle openers.
Does NOT change the direction of force.
Effort moves farther than Resistance (Load)
Results in an Increase in Force (mechanical advantage).

31. Resistance Force (load) is between fulcrum and Effort Force Effort moves farther than Resistance. Multiplies Effort Force, but does NOT change its direction

32. Third Class Lever
Effort force is applied between the fulcrum and the resistance force.
Examples include tweezers, hammers, and shovels tongs, or a human arm, fishing pole, baseball bat
Does NOT change the direction of force;
Produce a gain in speed and distance and a corresponding decrease in force.

33. Effort Force is between fulcrum and Resistance Force (load) Does not Multiply Force or Change it’s direction Resistance moves farther than Effort. Multiplies the distance the effort force travels

34. 5. Wheel and Axle
Wheel and Axle a large wheel rigidly secured to a smaller shaft (axle).
Turning the wheel also turns the axle
Turning the axle also turns the wheel

35. 5. Wheel and Axle
Wheel and Axle acts like 2nd class or 3rd class LEVER depending on if the Effort Force is Applied to the axle or the wheel

36. 5. Wheel and Axle Gears are sets of Wheel and Axles that mesh together
One gear turns the next IN THE OPPOSITE DIRECTION

37. 6. Pulley Pulley are wheels and axles with a groove around the outside
Can act as 1st or 2nd class levers.
Can simply change the direction of a force OR gain a mechanical advantage
Examples : flagpole, clothesline, cranes, fishing reel

38. 6. Pulley
fixed pulley - does not rise or fall with the load. (changes direction of force).
moveable pulley rises and falls with the load being moved.(creates a mechanical advantage)
Mechanical advantage = # of ropes that support the moveable pulley (2 ropes = MA of 2).

39. However, Some Output force is lost due to friction.
Efficiency
Remember: We said
Input Force x Input Distance
= Output Force x Output Distance
However, Some Output force is lost due to friction.
Efficiency compares the work output to the input. (is a percentage)
Efficiency = Work OUTPUT x Work INPUT
No machine has 100 percent efficiency due to friction.

40. Practice Questions
1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth.
2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec?
3. Using a single fixed pulley, how heavy a load could you lift?

41. Practice Questions
4. Give an example of a machine in which friction is both an advantage and a disadvantage.
5. Why is it not possible to have a machine with 100% efficiency?
6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.

42. Practice Questions
1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work.
2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W
3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.

43. Practice Questions
4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency.
5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient.
6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.

44. Inclined Plane Inclined plane = an even sloping surface.
makes it easier to move a weight from a lower to higher elevation.

45. Inclined Plane
Mechanical Advantage of an inclined plane = __Length of the Slope__ Height of Inclined Plane
It produces a mechanical advantage (need less force to move object) by increasing the distance through which the force must move.

46. Although it takes less force for car A to get to the top of the ramp, all the cars do the same amount of work.
A B C

47. Inclined Plane
A wagon trail on a steep hill will often traverse back and forth to reduce the slope experienced by a team pulling a heavily loaded wagon.
This same technique is used today in modern freeways which travel winding paths through steep mountain passes.

48. Wedge
The wedge is a modification of the inclined plane. Wedges are used as either separating or holding devices.
A wedge can either be composed of one or two inclined planes. A double wedge can be thought of as two inclined planes joined together with their sloping surfaces outward.

49. Screw The screw is also a modified version of the inclined plane.
While this may be somewhat difficult to visualize, it may help to think of the threads of the screw as a type of circular ramp (or inclined plane).

50. MA of an screw can be calculated by dividing the number of turns per inch.

52. However, Some Output force is lost due to friction.
Efficiency
Remember: We said
Input Force x Input Distance
= Output Force x Output Distance
However, Some Output force is lost due to friction.
Efficiency compares the work output to the input. (is a percentage)
Efficiency = Work OUTPUT x Work INPUT
No machine has 100 percent efficiency due to friction.

53. Practice Questions
1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth.
2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec?
3. Using a single fixed pulley, how heavy a load could you lift?

54. Practice Questions
4. Give an example of a machine in which friction is both an advantage and a disadvantage.
5. Why is it not possible to have a machine with 100% efficiency?
6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.

55. Practice Questions
1. Explain who is doing more work and why: a bricklayer carrying bricks and placing them on the wall of a building being constructed, or a project supervisor observing and recording the progress of the workers from an observation booth. Work is defined as a force applied to an object, moving that object a distance in the direction of the applied force. The bricklayer is doing more work.
2. How much work is done in pushing an object 7.0 m across a floor with a force of 50 N and then pushing it back to its original position? How much power is used if this work is done in 20 sec? Work = 7 m X 50 N X 2 = 700 N-m or J; Power = 700 N-m/20 sec = 35 W
3. Using a single fixed pulley, how heavy a load could you lift?Since a fixed pulley has a mechanical advantage of one, it will only change the direction of the force applied to it. You would be able to lift a load equal to your own weight, minus the negative effects of friction.

56. Practice Questions
4. Give an example of a machine in which friction is both an advantage and a disadvantage. One answer might be the use of a car jack. Advantage of friction: It allows a car to be raised to a desired height without slipping. Disadvantage of friction: It reduces efficiency.
5. Why is it not possible to have a machine with 100% efficiency? Friction lowers the efficiency of a machine. Work output is always less than work input, so an actual machine cannot be 100% efficient.
6. What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input. The effort force is the force applied to a machine. Work input is the work done on a machine. The work input of a machine is equal to the effort force times the distance over which the effort force is exerted.