1. Mrs Sedlock Principles of Chemistry and Physics
Work, Power, and Energy
Mrs Sedlock
Principles of Chemistry and Physics

2. Review
Newton’s Laws were used to predict and describe an object’s motion
In this unit we will discuss motion in terms of energy and work

3. Work
Work - when force acts on an object and causes displacement of the object
Force
Displacement
Cause
In order for work to be done there must be a force that causes a displacement

4. Examples of Work

5. Examples of work
A teacher applies a force to a wall and becomes exhausted.
A book falls off a table and free falls to the ground.
A waiter carries a tray full of meals above his head by one arm straight across the room at constant speed. (Careful! This is a very difficult question that will be discussed in more detail later.)
A rocket accelerates through space.

6. Work
Any part of a force that does not act in the direction of motion does NO WORK in an object

7. Negative Work
Sometimes force acts in the opposite direction of the displacement to prevent motion
Ex:
car skidding to a stop
Baseball player sliding into home plate

8. Calculating Work Work = force x displacement Unit of work = J (Joules)
1 J = 1 N*m
Ws work problems

9. Power

10. Power Power – is the rate of doing work
Doing work at a faster rate requires more power
to increase power, increase the amount of work done in a given amount of time
Or do the same amount of work in less time

11. Power
The snow blower can do more work in less time – so it has more power than the person shoveling

12. Calculating Power Power = work time Units Work is in Joules (J)
Time is in seconds (s)
Power is in watts (W) which is 1 Joule /second
Ex: a 40-watt lightbulb requires 40 Joules each second that it is lit

13. Calculating Power
You exert a vertical force of 72 Newtons to lift a box to a height of 1.0 meter in a time of 2.0 seconds. How much power is used to lift the box?
(hint: remember that work = force x displacement )
36 Watts

14. Horsepower
One horsepower (hp) = 746 Watts

15. slapshot physics

16. Work and Machines
drones

17. Machine Machines make work easier to do Change the size of the force
Or the direction of the force
Or distance over which a force acts

18. Increase force
Each rotation applies a small force over a large distance, but each rotation lifts the car a short distance
If a machine increases the distance over which you exert a force, then it decreases the amount of force you need to exert

20. Increasing distance
The oars act as a machine to push the boat through the water
Pulling the oar short distance near the boat translates to a large distance in the water – but you increase the force needed
A machine that decreases the distance through which you exert a force increases the amount of force

22. Change of direction
Some machines change the direction of the applied force
Pulling back on the handle of the oar causes its other end to move the opposite direction
Machines can change the direction of the force

23. Work Output
The force that is exerted by a machine is called the output force
The distance the output force is exerted through is the output distance
work output = output force x output distance

24. Work Input and Work Output
Because of friction, the work done by a machine is always less than the work done on the machine

25. Work input and work output
The force you exert on a machine is called the input force
the distance the input force acts through is called the input distance
The work done in this process is called the work input
Work input = input force x input distance

26. Work Input
For the oar-
the input force is the force exerted on the handle
The input distance is the distance the handle moves
The work input is the work you do to move the handle
You can increase the work input by increasing the input distance, the input force, or both

27. The force the oar on the water causes an equal and opposite reaction force to be exerted by the water on the oar – this reaction force propels the boat through the water
The only way to increase the work work output is to increase the amount of work you put into the machine

28. Mechanical Advantage and Efficiency

29. Mechanical Advantage
Mechanical advantage of a machine is the number of times that the machine increases an input force

30. Actual Mechanical Advantage
A loading ramp is a machine used to move heavy items into a truck
The longer the ramp, the less force is needed to lift a refrigerator into the truck

31. Actual Mechanical Advantage (AMA)
AMA = output force
input force

32. Actual Mechanical Advantage
If the ramp has a rough surface it will have less
mechanical advantage than a ramp with a
smooth surface
It takes a greater force to overcome the friction

33. Ideal Mechanical Advantage(IMA)
Ideal mechanical advantage of a machine is the mechanical advantage in the absence of friction
Because friction is always present, the actual mechanical advantage of a machine is always less than the ideal mechanical advantage

34. Ideal Mechanical Advantage(IMA)
IMA = input distance output distance

35. Ideal Mechanical Advantage(IMA)
A woman drives her car up onto wheel ramps to perform some repairs. If she drives a distance of 1.8 meters along the ramp to raise the car 0.3 meter, what is the ideal mechanical advantage of the wheel ramps?
IMA = input distance = 1.8 m = 6
output distance m

36. Efficiency
Efficiency – the percentage of work input that becomes work output- usually expressed as a percentage
The efficiency of ANY machine is always less than 100%

37. Efficiency
Efficiency = work output x 100%
work input

38. Quiz Review What is the unit for force? What is the unit for power?
What is the unit for distance/displacement?
What is the unit for time?
What is the unit for work?

39. Quiz review
You must exert a force of 4.5 newtons on a book to slide it across a table. If you do 2.7 Joules of work in the process, how far have you moved the book?

40. Quiz Review
A catcher picks up a baseball from the ground. If the unbalanced force on the ball is x Joules of work is done to lift the ball, how far does the catcher lift the ball?

41. Quiz Review
A machine has a work output of 8 joules and requires 10 joules of work input to operate. What is the machine’s efficiency?

42. Quiz review
What is the output distance of a machine with an input distance of 3.0 cm and an ideal mechanical advantage of 12?

43. Simple Machines

44. 6 Types of Simple Machines
Lever
Wheel and axle
Inclined plane
Wedge
Screw
Pulley

45. Simple machines
Many mechanical devices are combinations of the six types of simple machines

46. Lever Lever- a rigid bar that is free to move around a fixed point
- the fixed point is known as
the fulcrum

47. Lever There are 3 classes of levers based on the locations of
input force,
output force,
and the fulcrum

48. Lever First Class lever
Fulcrum of a first class lever is always between the input force and the output force
Mechanical advantage depends on location of the fulcrum

49. Lever
Second class lever- output force is between the input force and the fulcrum
Input distance is larger than output distance , which means you need less force
The mechanical advantage of a second class lever is always greater than 1

50. Lever
Third class lever – input force is between the fulcrum and the output force
Input distance is smaller than output distance
Mechanical advantage is less than 1

51. Levers
Levers
Paul Rabil

52. Lever

53. Wheel and Axle
Wheel and axle is a simple machine that consists of two disks or cylinders, each with a different radius
The outer disk is the wheel and the inner disk is the axle
The input force can be applied to the wheel or the axle

54. Wheel and Axle
To calculate the mechanical advantage of the wheel and axle
Can have a mechanical advantage less than or greater than 1
Mechanical advantage = radius of input
radius of output

55. Wheel and Axle

56. Inclined Plane
If the input distance is greater than the output distance, the input FORCE is DECREASED

57. Inclined plane
Inclined plane- a slanted surface along which a force moves an object to a different elevation
The ideal mechanical advantage of an inclined plane is the distance along the inclined plane divided by its change in height
IMA = distance of inclined plane
change in height
Teacher demo

58. Wedges and Screws
Wedges- v-shaped object that has inclined planes on the sides sloped toward each other
The sloping sides push the wood a small distance apart
Mechanical advantage
is greater than 1

59. Wedges and Screws Screw- an inclined plane wrapped around a cylinder
Screw that have threads closer together have a greater ideal mechanical advantage

60. Pulleys
Pulley is a simple machine that consists of a rope that fits into a groove in a wheel
Pulleys produce an output force that is different in size, direction, or both from the input force

61. Pulleys
The ideal mechanical advantage (IMA) of a pulley system is equal to the number of rope sections supporting the load being lifted
Three types of pulleys
Fixed Pulley
Movable pulley
Pulley system

62. Pulleys Fixed Pulley Wheel attached in a fixed location
Changes direction of the exerted force
IMA is 1 because the rope will lift the load the exact distance you pull the rope

63. Pulleys Movable Pulley Is attached to the object being moved
Reduce the input force

64. Pulleys
Pulley system
Mechanical advantage depends on how the pulleys are arranged
Each segment of the rope exerts a force equal to the force you exert on the rope
Pulleys

65. Compound Machines
Combination of two or more simple machines that operate together
The output force of one of the simple machines becomes the input force
for another
Ex:
Clocks
Bicycles

66. Compound Machines

67. Simple machines
Bill Nye Simple MAchines

68. Energy

69. Energy Energy is the ability to do work
Energy is transferred by a force moving an object over a specific distance
Sooooo
Work is a transfer of energy
Both are measured in Joules

70. Types of Energy Kinetic energy Potential energy Energy of motion
Energy of position, stored energy

71. if you double the mass, the KE is doubled
Kinetic Energy
The kinetic energy (KE) of an object depends on its mass (in kg) and speed (velocity v in meters per second)
KE=½ mv2
if you double the mass, the KE is doubled
if you double the speed, the KE is
quadroupled!

72. Practice problem
A 70 kg man is walking at a speed of 2.0 m/s. What is his kinetic energy?
KE = ½ mv m= 70 kg v = 2.0 m/s
KE = ½(70 kg) (2.0 m/s)2
KE = 140 J

73. Potential Energy
Potential energy is the energy with the potential to do work
Two common forms
Gravitational
Elastic

74. Gravitational Potential Energy
Potential energy that depends on an objects height is called gravitational potential energy

75. Gravitational Potential Energy
An object’s gravitational potential energy depends on its mass (m), height (h), and acceleration due to gravity (g)
Potential Energy (PE) = mgh

76. Elastic Potential Energy
Potential Energy of an object that is stretched or compressed is known as elastic potential energy
Something is considered to be elastic if it springs back to its original shape
Rubber band- energy you add is stored as potential energy

77. Forms of Energy Mechanical energy Thermal energy Chemical energy
Electrical energy
Electromagnetic energy
Nuclear energy

78. Mechanical Energy
Energy associated with motion

79. Thermal Energy
All particles of matter are in constant motion so they have kinetic energy
The total of the potential and kinetic energy of all microscopic particles make up its thermal energy

80. Thermal Energy

81. Chemical Energy Energy stored in chemical bonds
When bonds are broken, energy is released that can do work

82. Chemical Energy

83. Electrical Energy The energy associated with electrical charges
Electric charges can exert a forces that do work

84. Electrical energy

85. Electromagnetic Energy
Form of energy that travels as a wave

86. Nuclear Energy
Energy stored in atomic nuclei is nuclear energy

87. Nuclear Energy

88. How a Nuclear Power Plant Produces Electricity

89. Energy
Bill Nye Energy