1. Today’s Plan: Tests are graded Energy Lecture Work – Energy Lab
Homework: Lab and Handout

2. Energy Introduction What source/types of energy can you name?
We focus on “mechanical energy”.
But first…

3. Work = force X distance

4. To do work, you must:
Apply a force
Move something a distance

5. Unit of measure of work:
Joule
N m

6. I push a box… or does the box push me?
If I push with a steady force of 12 N for 6.0 meters
How much work did I do?

7. Energy = the ability to do work
Also measured in joules.

8. Power = work done / time interval

9. That darn box… If I push it those 6 meters in 4 seconds…
How much power do I use?

10. Unit of measure for power:
Watt 1 watt = joule/second

11. Mechanical Energy = Energy due to position or the movement of something

12. Two types of Mechanical Energy:
1. Potential Energy = energy with the potential to do work.

13. Kinetic Energy:
KE = ½ mv2
Energy of motion.

14. Kinetic Energy A 50 kg skier is moving at 10 m/s
Calculate the skier’s kinetic energy

15. Potential energy & gravity
When PE is due to its height above ground…
We call it “gravitational potential energy” (GPE).

16. GPE: work done against gravity
Force = weight =
Potential Energy = Work
Thus… G.P.E. = m g h (height)
Force X distance
Mass X gravity
Mass X gravity X distance

17. At the gym… You lift a 50 kg mass from the ground to 2 meters up.
Calculate the work done and the potential energy
50 kg x 9.81 m/s2 x 2 m = 981 J
Work done and PE are the same!

18. Power to the People Lab
A lab for the people, by the people and of the people!
People Power!!!

19. December 9 Plan of the Day
Energy and Work Notes continued…
Pulley Lab

20. Energy and Work Notes continued…

21. What is work…
force X distance

22. What is power…
Work / Time

23. What is energy…
Ability to do work

24. Quick review… If I push on the wall am I doing any work?
If the cart is moving at a constant velocity with no force acting on it, is there any work being done?

25. What is the unit for work?
Joules

26. What is the unit for power?
Watts

27. What is the units for energy?
Joules
Atlanta Olympics - Richard

28. Work and power! If you double the distance that a force is applied…
What happens to the work?
If you cut the time it takes to do a certain amount of work in half…
What happens to the power output?

29. Kinetic energy KE depends on mass and speed of object KE = ½ mv2
If you double the mass…
You double the KE
If you double the velocity…
You QUADRUPLE the KE

30. Kinetic Energy Throw the cans out the window
Have they lost their energy?
KE = ½ mv2
= ½ mass x speed2
What are you doing when you give something a push?
What happens to the thing being pushed?

31. Speed is squared! Let’s say you are driving at 10 m/s
And slam on your brakes –
Stopping in 10 meters
How far would you skid if you were going 20 m/s?
Assuming the same force…
How about 30 m/s?

32. Work – kinetic energy connection
If you do work on an object
you cause it to speed up.
Kinetic Energy is increased
Work = Change in energy
(force X distance) = Δ KE
W = Δ ½ mv2

33. Work – Kinetic Energy Work = ΔKE
F x d = ½ mv2
If the car has a mass of 1000 kg and is moving at 10 m/s
What is the kinetic energy?
What is the force you need to apply to stop the car in 20 meters?

35. Conservation of energy: Energy is not created or destroyed – the total amount never changes, it only changes form.

36. Mechanical Energy Imagine a rock at the bottom of a valley.
Does it have energy?
Now imagine that rock poised at the edge of a cliff.
How are they different?

37. Mechanical Energy The 2 most common forms:
Energy due to position
Energy due to motion
Mechanical Energy = the sum of the 2
Potential energy
Kinetic energy

38. The total ME stays the same
How much PE?
KE?

39. We use machines to multiply force or change direction.

40. In a closed, ideal system, the work that is input is the same as the work output.
Work in = Work out

41. Thus…
Forcein X Distancein = Forceout X Distanceout

42. What is the purpose of this pulley?

43. Pulleys IMA can also be calculated by counting the number of support ropes!!

44. Lab Pulleys – 5 different configurations Set them up and determine:
The work you do to lift the mass 0.1 m
Force (that you apply) x distance (that you pull)
Compare it to the work done by the work done on the mass
Its weight (force) x distance lifted (0.1 m)

45. Mechanical Advantage and Efficiency Lever Lab
December 11
Mechanical Advantage and Efficiency
Lever Lab

46. How many strings segments are lifting the object?

47. And now?

49. Review – what is energy?
The ability to do work…

51. Potential to Kinetic

52. Or a dart being shot…

53. In a closed, ideal system
Work in = Work out

54. Let’s look at pulleys & levers…

55. Machines are used to multiply force or change direction of the force.

56. Work in is what you put into the system. (Force and Distance)

57. “Work out”: the object.
(force (weight) and distance)

58. Mechanical advantage…
How much the machine multiplies the force.
Higher the MA = greater advantage
MA = force out / force in

59. Ideal Mechanical Advantage
Assumes 100% efficient!
IMA = distance input / distance output

60. IMA ignores Mr. Friction
So your Actual MA…
Will be less than ideal

61. Actual Mechanical Advantage
Takes into account energy lost…
AMA = force output / force input

62. Example problem: pulley
You pull with a force of 12 N to lift an object that weighs 30 N
You pull the string 3 meters to lift it 1 meter
What is your IMA and AMA?

63. How does a lever work? Fulcrum Distances to the fulcrum
This is a class 1 lever
5 meters 2 meters
30 Newtons
15 Newtons

64. Type Two Lever
IMA =
AMA =
5 meters meters
20 Newtons
15 Newtons

65. Type Three Lever
5 meters meters
20 Newtons
15 Newtons

66. Efficiency...
The percent of work you do that is transformed into useful work output
Efficiency = work out/work in x 100%

67. Another way to figure it out…
Efficiency = AMA X 100%
IMA
In the real world – efficiency must always be less than 100%.

68. Example Problem:
You use a pulley to lift a 2000 Newton tarp full of leaves 10 feet.
You only have to use a force of 800 Newtons but you have to pull the rope 30 feet.
Calculate the AMA and IMA of the system.
What is the efficiency of the pulley system?

69. To the lab!
Exploring levers…

70. December15
More Machines

71. So back to simple machines…

74. Work in is what you put into the system. (Force and Distance)

75. Work out is the affect on the object. (force (weight) and distance)

76. Machines are used to multiply force or change direction of the force.

77. Example Problem:
You use a pulley to lift a 20 Newton mass 15 centimeters. You pull down 30 centimeters on the rope. With how much force do you pull down?

78. Example Problem:
You push a box up an incline. You push the box a distance of 50 centimeters with a force of 90 Newtons. The box is actually 120 Newtons. How far are you actually raising the box?

79. Today’s Plan: Review of Mechanical Advantage and Efficiency
Incline planes, wheel and axle, wedge
More Machines Lab

80. Review What does it mean when a machine has a high MA?
How do you calculate efficiency?
If you calculate your IMA
What should you anticipate about your AMA?

81. Example Problem
The distance from the rock to the fulcrum is 30 centimeters and the distance from my hand to the fulcrum is 40 centimeters. What is the IMA?
Output distance
Input distance I

82. Example Problem
I hike a hill that has a vertical elevation of 3000 ft.
The trail wraps around the mountain and I actually have to hike ft.
What is the IMA of the trail?

83. Example Problem
I have the pulley system to the right – how far does the monkey have to pull to raise the elephant 10 centimeters?

84. Example problem
To push the 30 Newton box up the ramp to the truck, I have to use 10 Newtons of force. What is the AMA of the ramp?

85. Example Problem
I use a lever to dislodge a 30 Newton boulder and I have to put 10 Newtons of force on the far side of the lever. What is the AMA of the lever?

86. Example Problem:
You use a pulley to lift a 2000 Newton tarp full of leaves 10 feet.
You only have to use a force of 800 Newtons but you have to pull the rope 30 feet.
Calculate the AMA and IMA of the system.
What is the efficiency of the pulley system?

87. Example Problem:
A pulley system has 3 supporting ropes, but you determine that the actual mechanical advantage is What is the efficiency of the pulley system?

88. Pulleys Number of support ropes can be used to determine IMA.
Can use din/dout for IMA
Use Fout/Fin for AMA

89. Inclined Plane
Use din/dout for IMA
Use Fout/Fin for AMA
45 Newton box

90. Lever
Can use din/dout for IMA
Use Fout/Fin for AMA

91. Wheel and Axle Use Fout/Fin for AMA
IMA = Radius of wheel / radius of axle
(R/r)
Use Fout/Fin for AMA

92. Wedge
IMA = Length of wedge / thickness of wedge
Use Fout/Fin for AMA

93. The screw
What machine does a screw remind you of?

94. What happens
When you combine machines?
                        

95. Your Machine Groups of 2 or 3
Design must include 3 machines with different MA
Total IMA of the machines must be between 15 and 30

96. Today’s Plan: Quiz Review Notes over compound machines
Lab: Design, Construct, and Measure Complex Machines

97. Compound Machines
The mechanical advantage of a compound machine is the product of the individual mechanical advantages.

98. Why are bolt cutters so effective?

100. Today in lab, I want:
A good diagram of your machine – everyone must turn in a separate diagram.
Listed neatly next to each machine, its IMA.
And the dimensions I need to verify your calculation
Measure the AMA of the total machine.
Determine the IMA of total machine.
Determine efficiency of the machine….
Turn in lab sheet with questions and diagram

101. Review: Energy, Work & Machines
After winter break…

102. Energy, Power, Work? Your mass is 65 kg Calculate your weight
If you climb the stairs
6 meters…
How much energy did you use?
What is your PE at this point?

103. Work II You push your bike to school How much work do you do?
Applying a force of 12 N for 5 meters
How much work do you do?
If you start at rest, what is your kinetic energy at the end?
How fast are you going?

104. Conservation of energy
You throw a 10 kg turkey out of the second story of your house (12 m).
What is the PE at the top?
What is the PE and KE at 4 meters?

105. Power
You accomplish 3,000 J of work in 15 seconds. What is your power use?

106. Machines
An incline plane has a height of 2 meters and is 12 meters long.
What is the IMA?
If you push a 400 N barrel up the ramp what is the minimum force you can apply?
If you have to apply 100 N
Determine the IMA, AMA and efficiency

107. Draw the following machines
Label the critical parts and distances:
Pulley with a 4:1 IMA
Wheel and axle with a 2:1 IMA
Incline plane with a 5:1 IMA
Class II lever with a 3:1 IMA