1. Energy, Work and Simple Machines
Chapter 10
Physics

2. Objectives: The student will be able to:
explain the relationship between simple machines and work.
Demonstrate a knowledge of the usefulness of simple machines.
Differentiate between ideal and real machines in terms of efficiency.
Describe a compound machine.

3. Machines Machines can do any of the following;
Machines can Multiply the Force (Lever)
Change the Direction of the Force (Pulley)
Change the speed in which the force acts (Gears)

4. Force is a push or pull that changes the motion or shape of an object.
Example: I push a bookshelf to move it.

5. Energy is the ability to do work.
Example: I must have energy to run the mile.

6. Work is the result of force moving an object.
Example – Picking up something heavy is hard work!

7. Gravity is the force that constantly pulls objects toward Earth.

8. Machines Most machines make work easier by multiplying the Force!
Machines never Multiply the Work!
When using a machine there is always a Work put into the machine (WIN) and a Work the machine puts out (WOUT).
Ideally, the WIN = WOUT in an ideal machine (no friction).

9. 10.2 Machines
The best way to analyze what a machine does is to think about the machine in terms of input and output. 9

10. Machines
How Does a Machine multiply the force without multiplying the Work?
Answer: If a machine multiplies the Input Force (FIN), then the machine must act over a larger Displacement (dIN)!
Remember, W = Fd

11. Machines WIN = WOUT FIN dIN = FOUT dOUT
FIN will be small so dIN will be large!
FOUT will be large so dOUT will be small!

12. Types of Simple Machines
Simple Machine (SM) – a machine with one or two moving parts.
There are six types of Simple Machines:
1. Lever Inclined Plane
2. Pulley Wedge
3. Wheel and Screw
Axle

13. Example: seesaw, crowbar, baseball bat, rake
Lever –made of a board or bar set on top of a fulcrum. It is used to lift weight
Example: seesaw, crowbar, baseball bat, rake

14. Classes of Levers “First Class Lever” Examples: Seesaw
A first-class lever is a lever in which the fulcrum is located between the input effort and the output load.
In operation, a force is applied (by pulling or pushing) to a section of the bar, which causes the lever to swing about the fulcrum, overcoming the resistance force on the opposite side.
The fulcrum may be at the center point of the lever as in a seesaw or at any point between the input and output.
This supports the effort arm and the load.
Examples:
Seesaw
Scissors (double lever)

15. First Class Lever fulcrum Effort Resistance
Fulcrum is between EF (effort) and RF (load) Effort moves farther than Resistance. Multiplies EF and changes its direction The mechanical advantage of a lever is the ratio of the length of the lever on the applied force side of the fulcrum to the length of the lever on the resistance force side of the fulcrum.

16. Examples of first class levers
Common examples of first-class levers include
crowbars,
scissors,
pliers,
tin snips
and seesaws.

17. Second Class Lever Effort Resistance
RF (load) is between fulcrum and EF Effort moves farther than Resistance. Multiplies EF, but does not change its direction The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance from the resistance force to the fulcrum.

18. Three Lever Classes Always multiplies a force. Second class lever E R
Explanation
Three Lever Classes
Second class lever
Resistance is located between the effort force and the fulcrum.
Always multiplies a force
Example: Wheelbarrow E R F
Always multiplies a force.
8/23/04

19. Examples of Second class levers
In a second class lever the input effort is located at the end of the bar and the fulcrum is located at the other end of the bar, opposite to the input, with the output load at a point between these two forces.
Examples:
Paddle
Wheelbarrow
Wrench

20. Examples of second-class levers
Examples of second-class levers include:
nut crackers,
wheel barrows,
doors,
and bottle openers.

21. Third Class Lever
EF is between fulcrum and RF (load) Does not multiply force Resistance moves farther than Effort. Multiplies the distance the effort force travels The mechanical advantage of a lever is the ratio of the distance from the applied force to the fulcrum to the distance of the resistance force to the fulcrum

22. Classes of Levers Examples: Hockey Stick Tweezers Fishing Rod
“Third Class Lever”
Examples:
Hockey Stick
Tweezers
Fishing Rod
For this class of levers, the input effort is higher than the output load, which is different from second-class levers and some first-class levers.
However, the distance moved by the resistance (load) is greater than the distance moved by the effort.
In third class levers, effort is applied between the output load on one end and the fulcrum on the opposite end.

23. Explanation
Three Lever Classes
Third class lever
Effort force located between the resistance and the fulcrum.
Effort arm is always shorter than resistance arm
MA is always less than one
Example: Broom E R F
There is an increase distance moved and speed at the other end.
Other examples are baseball bat or hockey stick.
8/23/04

24. Examples of Third Class Levers
Examples of third-class levers include:
tweezers,
arm hammers,
and shovels.
Third class lever in human body.

25. Example : flagpole, clothesline, cranes, fishing reel
Pulley – made of rope and string wound around a reel to change the direction of a force.
Example : flagpole, clothesline, cranes, fishing reel

26. Example: steering wheel, doorknob, screwdriver
Wheel and Axel – a wheel that turns on a post to help move things quickly and easily
Example: steering wheel, doorknob, screwdriver

27. Inclined Plan – a slanted surface to make lifting easier
Example: ramp, stairs

28. Example: knife, door wedge, ax
Wedge – two inclined planes together used to raise an object or split an object.
Example: knife, door wedge, ax

29. Example: drill bit, screws
Screw – an inclined plane wrapped around a pole or shaft that is used to hold materials together or drill holes.
Example: drill bit, screws

30. Compound Machine – two or more simple machines working together.
Examples:
Bike
Car

31. Mechanical Advantage
Mechanical Advantage (MA) – is the number of times a machine multiplies the Input Force (FIN)
Example:
MA = 2 Means the machine doubles the force you put into it.
MA = 10 Means the machine multiplies the force put into it by 10.

32. 10.2 Mechanical Advantage
Mechanical advantage is the ratio of output force to input force.
For a typical automotive jack the mechanical advantage is 30 or more.
A force of 100 newtons (22.5 pounds) applied to the input arm of the jack produces an output force of 3,000 newtons (675 pounds)— enough to lift one corner of an automobile.

33. Mechanical Advantage MA >1 (Machine multiplies the force)
MA < 1(Machine multiplies the distance)
MA = 1(Machine does not multiply either force or distance. Probably only changes the direction to the force.)

34. Mechanical Advantage
To find the Mechanical Advantage (MA) of a machine, we take the ratio of the Resistance Force (Fr) to the Effort Force (Fe)
Effort Force (Fe) – is the force applied to the machine
Resistance Force (Fr) – is the force the machine applies to the object

35. 10.2 Mechanical Advantage MA = Fo Fi Output force (N) Mechanical
Input force (N)

36. Ideal Mechanical Advantage (IMA)
The Ideal Mechanical Advantage (IMA) is the largest possible MA a machine can have if the machine operated without friction.
To find the Ideal Mechanical Advantage (IMA) of a machine you take the ratio of the Effort Distance (de) over the Resistance Distance (dr)

37. Calculating MA and IMA
To calculate MA we use the Forces (Fr and Fe). Since Friction is a force, Friction affects MA. MA = Fr/Fe
To calculate IMA we use the distances (dr and de). Friction does not affect IMA. IMA = de/dr
MA has No Unit!! It’s a number telling how many times the force is multiplied!

38. Ideal Mechanical Advantage and Actual Mechanical Advantage
The Actual Mechanical Advantage (MA) is always less than the IMA (MA < IMA) because of Friction.
Machines are designed with an IMA
Machines are tested to find Actual MA

39. Input/Effort and Output/Resistance
Note from this point on:
Effort = Input
(FIN = Fe and dIN = de)
Resistance = Output
(FOUT = Fr and dOUT = dr)
WIN = WOUT (Ideal Machine)
Fede = Frdr

40. Compound Machines
Compound Machine – any combination of two or more simple machines
Examples: Axe, Shovel, Scissors
Compound Machines have a higher Mechanical Advantage (MA) because they are made up of multiple machines

41. Mechanical Advantage of Compound Machines
To calculate the Mechanical Advantage (MA) of a Compound Machine (CM), you multiply the Mechanical Advantages of all the Simple Machines in the Compound Machine
MACM = MASM#1 x MASM#2 x MASM#3 x …

42. Efficiency
Efficiency is the ratio of the useful work you get out of a machine (WOUT) over the work you put into a machine (WIN)
In an ideal world (no friction);
WOUT = WIN therefore;
WOUT/WIN = 1

44. Efficiency In the real world (with friction); WOUT < WIN therefore;
We express Efficiency as a Percentage by multiplying the ratio by 100%
Ideal World Efficiency = 100%
Real World Efficiency < 100%

45. Efficiency We can use different equations for Efficiency
Eff = (WOUT/WIN) x 100%
Eff = (Frdr/Fede) x 100%
Eff = (MA/IMA) x 100%

46. Efficiency and Machines
Simple Machines have a small MA but work with a high Efficiency.
Compound Machines have a high MA but work with a lower Efficiency.
The more complicated the machines the greater the MA but the lower the Efficiency!

47. The Human Machine Levers – Muscles and Tendons
Wedges – Teeth and Finger Nails
Your Body uses many Simple and Compound machines to create Mechanical Advantage
Human Walking Machine Page 273

48. Closure

49. Practice Question
Using a single fixed pulley, how heavy a load could you lift?

50. Practice Question
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.

51. Practice Question
Give an example of a machine in which friction is both an advantage and a disadvantage.

52. Practice Question
Give an example of a machine in which friction is both an advantage and a disadvantage.
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.

53. Practice Question
Why is it not possible to have a machine with 100% efficiency?

54. Practice Question
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.

55. Practice Question
What is effort force? What is work input? Explain the relationship between effort force, effort distance, and work input.

56. Practice Question
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 time the distance over which the effort force is exerted.

57. Elaboration Simple Machines Transparency 10-2 Lever Lab
Energy Lab – work input and Output energy
Levers in the Human Body
Page 272 #s 25 and 26

58. Closure
Kahoot – 10.2