1. Potential & Kinetic Energy
Chapter 4
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3. Energy makes change possible.
What is energy ?
Wherever you are sitting as you read this, changes are taking place—light bulbs are heating the air around them, the wind might be rustling leaves, or sunlight might be glaring off a nearby window. Every change that occurs—large or small—involves energy.
Energy makes change possible.
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4. 5 Different Forms of Energy
electrical energy
chemical energy
radiant energy
thermal energy
kinetic energy
Is the chemical energy stored in food the same as the energy that comes from the Sun or the energy stored in gasoline?
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7. Electrical energy
Radiant Energy
                                    
Nuclear Energy

10. Different Forms of Energy
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11. Different Forms of Energy
Radiant energy from the Sun.
Radiant energy travels a vast
distance through space to Earth,
warming the planet and providing energy that enables green plants to grow.
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12. Kinetic Energy
Kinetic energy is the energy a moving object has because of its motion.
The kinetic energy of a moving object depends on the object’s mass and its speed.
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13. Kinetic Energy Kinetic Energy is energy that is in motion.
Moving water and wind are good examples of kinetic energy.
Electricity is also kinetic energy because even though you can't see it happen, electricity involves electrons moving in conductors.

14. Potential Energy
Even motionless objects can have energy. This energy is stored in the object.
A hanging apple in a tree has stored energy
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15. Potential Energy
Stored energy due to position is called potential energy.
If the apple stays in the tree, it will keep the stored energy due to its height above the ground.
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16. Potential Energy Energy is measured in the amount of "work" it does.
Potential Energy is stored energy.
Examples of potential energy are oil sitting in a barrel, or water in a lake in the mountains. This energy is referred to as potential energy, because if it were released, it would do a lot of work.

19. Gravitational Potential Energy
Anything that can fall has stored energy called gravitational potential energy.
Gravitational potential energy (GPE) is energy stored by objects due to their position above Earth’s surface.
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20. Gravitational Potential Energy
On Earth the acceleration of gravity is 9.8 m/s2, and has the symbol g.
Like all forms of energy, gravitational potential energy is measured in joules.
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21. Gravitational Potential Energy
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22. A 5 kg book is perched on a shelf 2 meters above the floor
A 5 kg book is perched on a shelf 2 meters above the floor. How much stored energy does that book possess?
Shelf
GPE = (5 kg) X ( 9.8 m/s²) X (2 m)
GPE = 98 Joules
Floor
Gravitational potential energy – (GPE) is energy stored by objects due to their position above Earth’s surface
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24. Elastic Potential Energy
The stretched rubber band had energy stored as elastic potential energy.
Elastic potential energy is energy stored by something that can stretch or compress, such as a rubber band or spring.
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25. Chemical Potential Energy
Gasoline stores energy in the same way as food stores energy-in the chemical bonds between atoms.
Energy stored in chemical bonds is chemical potential energy.
Chemical Energy
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26. Chemical Potential Energy
Energy is stored in the bonds that hold the carbon and hydrogen atoms together and is released when the gas is burned. In this chemical reaction, chemical potential energy is released
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27. Potential to Kinetic Energy Conversions
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28. Potential - kinetic Energy Conversions

29. Pendulum Energy Conversions

32. Energy Transformations in Projectile Motion
Energy transformations also occur during projectile motion when an object moves in a curved path.

33. Energy of a Slinky

34. Energy conversions of a tossed ball

35. Roller coaster Energy Conversions

37. Roller coaster Energy Conversions

38. Energy Conversions

39. The Law of Conservation of Energy
The law of conservation of energy states that energy cannot be created or destroyed.

40. Energy conservations Energy Conservation
                      
Total energy is the sum of both types of energy.

41. The Law of Conservation of Energy
Energy can change from one form to another, but the total amount of energy never changes.

42. Conservation of Energy
A light bulb converts electrical energy into thermal energy and light energy.
Gasoline in a car converts chemical potential energy into kinetic energy of a moving car.
Green plants convert light energy into chemical energy potential energy.

43. Conservation of Energy
Mechanical energy = Potential energy + Kinetic Energy in a system.
As an object falls, its potential energy changes to Kinetic energy. However the mechanical energy stays the same.

44. Law of Conservation of Energy
The total amount of Energy in the Universe always stays the same.
“Energy cannot be created or destroyed but it can change form but the total amount of energy remains the same.”
When energy changes form, some of the energy is converted to heat energy because of friction. This heat energy that can’t be used do to work.

46. Work & Power

47. Work & Power
Work: in order to do work on an object, the object must move.
Work = Force X Distance
Unit (SI) for work = Joule
The Joule is the name for: N-m
1N = kg/m/s²

48. Work

49. Power Power is the rate at which work is done.
To do work quickly it requires more power.
Power = Work / Time
Unit (SI) for Power is the Watt.
Watt = Joule / Second

50. Power

51. Using Machines
Conserving Energy
The amount of energy the machine transfers to the object cannot be greater than the amount of energy you transfer to the machine.
A machine cannot create energy, so Wout is never greater than Win.

52. Using Machines
Conserving Energy
When a machine is used, some of the energy transferred changes to heat due to friction.
The energy that changes to heat cannot be used to do work, so Wout is always smaller than Win.

53. Work Makes Something Move
Remember that a force is a push or a pull. In order for work to be done, a force must make something move.
Work is the transfer of energy that occurs when a force makes an object move.
If you push against the desk and nothing moves, then you haven't done any work.
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54. Doing work
For example, when you lift a stack of books, your arms apply a force upward and the books move upward. Because the force and distance are in the same direction, your arms have done work on the books.
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55. Force and Direction of Motion
Work
Force and Direction of Motion
When you carry books while walking, you might think that your arms are doing work.
However, in this case, the force exerted by your arms does no work on the books.
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56. Work done is zero when displacement is zero
Work done is zero when displacement is zero. This happens when a man pushes a wall. There is no displacement of the wall. Thus, there is no work done.
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57. Work and Energy When work is done, a transfer of energy always occurs.
This is easy to understand when you think about how you feel after carrying a heavy box up a flight of stairs.
You transferred energy from your moving muscles to the box and increased its potential energy by increasing its height.
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58. Calculating Work
The amount of work done depends on the amount of force exerted and the distance over which the force is applied.
When a force is exerted and an object moves in the direction of the force, the amount of work done can be calculated as follows.
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59. Work
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60. Solve for work Solve for force Solve for distance Solve for total work
        
Solve for work
Solve for force
Solve for distance
                             
Solve for total work W
 = 
work
Wtotal
total work F
force  d
distance  m
mass 
vinitial
initial velocity
vfinal
final velocity
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62. Power
Power is the amount of work done in one second. It is a rate—the rate at which work is done.
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63. Calculating Power
To calculate power, divide the work done by the time that is required to do the work.
The SI unit for power is the watt (W). One watt equals one joule of work done in one second.
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64. Power is the rate of work done in a unit of time.
The unit of the power from the equation given above, joule/s, however, we generally use the unit of power as watt.
1 joule/s = 1watt
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65. 12/2/2018
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66. Work & Power
Work: in order to do work on an object, the object must move.
Work = Force / Distance
Unit (SI) for work = Joule
The Joule is the name for: N-m
1N = kg/m/s²
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67. Work
Power and Energy
Just as power is the rate at which work is done, power is also the rate at which energy is transferred.
When energy is transferred, the power involved can be calculated by dividing the energy transferred by the time needed for the transfer to occur.
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68. Work & Power
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69. What is a machine? A machine is a device that makes doing work easier.
Using Machines
What is a machine?
A machine is a device that makes doing work easier.
Machines can be simple.
Some, like knives, scissors, and doorknobs, are used everyday to make doing work easier.
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70. Using Machines
Ideal Machines
Suppose the ideal machine increases the force applied to it.
This means that the output force, Fout, is greater than the input force, Fin.
Recall that work is equal to force times distance.

71. Using Machines
Ideal Machines
If Fout is greater than Fin, then Win and Wout can be equal only if the input force is applied over a greater distance than the output force is exerted over.

72. Using Machines
Mechanical Advantage
The ratio of the output force to the input force is the mechanical advantage of a machine.
The mechanical advantage of a machine can be calculated from the following equation.

73. Using Machines
Efficiency
Efficiency is a measure of how much of the work put into a machine is changed into useful output work by the machine.
A machine with high efficiency produces less heat from friction so more of the input work is changed to useful output work.

74. Calculating Efficiency
Using Machines
Calculating Efficiency
To calculate the efficiency of a machine, the output work is divided by the input work.
Efficiency is usually expressed as a percentage by this equation:

75. Calculating Efficiency
Using Machines
Calculating Efficiency
To calculate the efficiency of a machine, the output work is divided by the input work.
Efficiency is usually expressed as a percentage by this equation: