1. Chapter 4 Energy

2. Chapter 4 Energy

3. Even you are changing as you sit here and breath.
What is Energy?
Whereever you are sitting, changes are taking place –
1. light bulbs are heating the air around them
2. the wind might be rustling leaves
3. or sunlight might be glaring off a nearby window
Even you are changing as you sit here and breath.

4. Every change that occurs, large or small, involves ENERGY.

5. Imagine a baseball flying through the air
Imagine a baseball flying through the air. It hits a window causing the glass to break.
The window changed from a solid sheet of glass to a number of broken pieces.
The moving baseball caused the change- a moving baseball has ENERGY.

6. You also use energy when you are walking up and down the halls at school, or eating your lunch.
Even when you are yawning in my class.

7. Turn on your CD player and sound comes out.
Turn on an electric light and a dark room becomes bright.
Turn on your CD player and sound comes out.
In both situations, energy moves from one place to another. Theses changes are different form each other, and differ from the from the baseball and window

8. Energy has several different forms
Electrical
Chemical
Radiant
Thermal
Mechanical
Nuclear

9. If you have $100, you could store it in a variety of forms.
Cash in wallet
Bank account
Travler’s checks
Gold or silver coins.
Regardless of the form. MONEY IS MONEY

10. Is energy from the sun the same as chemical energy stored in food?
Yes. They are only different forms of the same thing.

11. When you think of energy you may think about action or objects in motion.
An object in motion does have energy

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

13. KE = 1/2mv2 The SI unit of energy is the JOULE abbreviated J
Kinetic energy (joules) = ½ mass (kg) x velocity2 m/s
KE = 1/2mv2
The SI unit of energy is the JOULE abbreviated J

14. A Yeti whose mass is 60 kg is moving at a speed of 3 m/s
A Yeti whose mass is 60 kg is moving at a speed of 3 m/s. What is the Yeti’s kinetic energy?
A J
B. 310 J
C. 450
Answer : A

15. What is the kinetic energy of a baseball moving at a speed of 40 m/s if the baseball has a mass of 0.15 kg?
120 J
250 J
900 J
Answer : A

16. An ATV moving at a speed of 20 m/s has a kinetic energy of 300,000 J
An ATV moving at a speed of 20 m/s has a kinetic energy of 300,000 J. What is the ATV’s mass?
2000 kg
1500 kg
2400 kg
Answer : B

17. A girl has a mass of 80 kg and a kinetic energy of 4,000 J
A girl has a mass of 80 kg and a kinetic energy of 4,000 J. What is the girl’s speed?
5 m/s
20 m/s
10 m/s
Answer : C

18. Answer: D __________ is the ability to cause change. A) Momentum
B) Work
C) Power
D) Energy

19. Answer : A Which of the following objects has kinetic energy?
A) a ball rolling across the floor
B) a bicycle parked at the top of a hill C) leaves lying on the ground beneath a tree
D) a sunny windowsill

20. POTENTIAL ENERGY POTENTIAL ENERGY –is stored energy.
Motionless objects also have energy.
This energy is stored in the object.

21. ELASTIC POTENTIAL ENERGY
ELASTIC POTENTIAL ENERGY = is energy stored by something that can stretch or compress. (spring, rubber band etc….)
A Stretched rubber band has elastic potential energy.
The elastic potential energy in the stretched rubber band was converted to kinetic energy when you released the band.

23. CHEMICAL POTENTIAL ENERGY
CHEMICAL POTENTIAL ENERGY = Is energy stored in chemical bonds.
Breakfast cereal and gasoline contain stored energy. They store it in the chemical bonds.

24. ELECTRICAL AND NUCLEAR POTENTIAL ENERGY
Another form of potential energy is ….
Nuclear potential energy – is the energy stored in the nuclei of atoms
Electrical potential energy – is the stored energy due to the position of an electric charge.

25. GRAVITATIONAL POTENTIAL ENERGY
Anything that can fall has stored energy called GRAVITATIONAL POTENTIAL ENERGY
GPE – is energy stored by objects due to their position above the Earth’s surface.

26. GRAVITATIONAL POTATIONAL ENERGY = is stored energy due to position.
The hanging apple has energy because of it position above the Earth’s surface.

27. The GPE of an object depends on the object’s mass and height above the ground.
It can be calculated by the following equation:
Gravitational potential energy (Joules) = mass x gravity x height
GPE (“J”) = mgh

28. If you have objects on a book shelf. They are all on different shelves
If you have objects on a book shelf. They are all on different shelves. Which of the objects would have the most gravitational potential energy?

29. What if two objects are on the same shelf
What if two objects are on the same shelf. Which object would have the greatest GPE?

31. Gravity is the driving force of a roller coaster
Gravity is the driving force of a roller coaster. From the moment the roller coaster train passes the peak of the lift hill, it is the acceleration due to gravity that brings it back to the beginning. When the train is released from the top of the lift hill, gravity pulls it down. The train begins slowly, then picks up speed as it approaches the bottom of the hill. As it begins to climb the next hill, the speed decreases. This is because of the acceleration due to gravity, which occurs at 9.80m/s2 straight down toward the center of the Earth.
The initial hill, or the lift hill, is the tallest in the entire ride. As the train is pulled to the top, it is gaining potential, or stored energy. The higher the lift, the greater the amount of potential energy gained by the train. This is shown by the equation for potential energy:
Ug = mgh

32. Answer : B =274J
What is the gravitational potential energy of a ceiling fan that has a mass of 7 kg and is 4 m above the ground?
350 J
274 J
456 J

33. Find the height of a baseball with a mass of 0
Find the height of a baseball with a mass of 0.15 kg that has a GPE of 73.5 J
50 m
45 m
35 m
Answer : A

34. What is the mass of a hiker 200 m above the ground if his GPE is 117,600 J?
50 kg
45 kg
60 kg
Answer : C

35. Find the GPE of a coffee mug with a mass of 0.3 kg on a 1 m high desk.
A J
B J
C J
Answer : B

36. Find the kinetic energy of a ball with a mass of 0
Find the kinetic energy of a ball with a mass of 0.06 kg moving at 50 m/s.
75 J
65 J
45 J
Answer: A

37. Answer : A Which of the following objects has potential energy?
A) a glass sitting on a table
B) a ball rolling across the floor
C) a bicycle coasting down a hill
D) a bowling ball knocking over a pin

38. Describe three situations in which the gravitational potential energy of an object changes.
Object is lowered
Raised higher
Mass changes.

39. An 80 kg diver jumps from a 10 m high platform
An 80 kg diver jumps from a 10 m high platform. What is the GPE of the diver halfway down.
GPE = 3900 J

40. Conservation of Energy
You use many devices every day that convert one form of energy to other forms.
Light bulb transforms electrical energy into light so you can see.
The warmth you feel around the bulb is evidence that some of the electrical energy is transformed into thermal energy “heat”

41. What other devices have you used today that use electrical energy?
Alarm clock
Curling iron
Toaster
CD player
Video game

42. Transforming chemical energy
Fuel stores energy in the form of chemical potential energy.
Car or bus runs on gasoline.
The engine transforms the CPE into kinetic energy of the moving car or bus.

43. An electric spark ignites a small amount of fuel.
The burning fuel produces thermal energy.
Chemical energy is changed to thermal energy
The thermal energy causes gases to expand and move parts of the bus producing kinetic energy.

44. Some energy transformations are less obvious.
Every green plant converts light energy from the Sun into energy stored in chemical bonds (CPE) in the plant.
If you eat the plant, the CPE is transformed into other forms of energy by your body.

46. Conversions between kinetic and potential energy.
You have experienced many situations that involve conversions between potential and kinetic energy.
ex. Launching a rubber band, riding a bike
To understand the energy conversions, it is helpful to understand Mechanical Energy.

47. Mechanical Energy – is the total amount of potential and kinetic energy in a system and can be expressed by this equation.
Mechanical energy = potential energy +kinetic energy
ME = KE+PE

48. If two vases were to fall
If two vases were to fall. As they fall and begin moving, they have kinetic energy as well as GPE. As the vases get closer to the ground, their GPE decreases. At the same time, they are moving faster, so their kinetic energy increases. The vase that was higher above the floor has fallen a greater distance. As a result the vase that initially had more GPE will be moving faster and have more kinetic energy when it hits the floor.

49. Energy transformation occurs during projectile motion when an object moves in a curved path.
When the ball leaves the bat it has mostly Kinetic Energy. As the ball rises its velocity decreases so its KE must decrease also.
However, as the ball rises, the Gravitational Potential Energy increases and the KE decreases.
The Mechanical Energy of the ball remains constant as it rises and falls.

50. When you ride on a swing is an example of how kinetic energy changes to potential energy.
Even though it is changing from one form to another the Mechanical Energy remains the same.

51. ME = PE + KE PE = 100 J KE= 0 J PE = 100 J KE = 0 J PE = 0 J

53. When you ride on a roller coaster
When you ride on a roller coaster. You are experiencing a change of Potential Energy to Kinetic Energy many times throughout the ride.

54. A large part of the thrill of the rollercoaster is the greater the GPE at the top of the hill the greater the kinetic energy increase as you ride down the hill.

55. As the roller coaster train begins its descent from the lift hill, its velocity increases. This causes the train to gain kinetic energy, which is the energy of motion. The faster the train moves, the more kinetic energy the train gains.
Because the mass is constant, if the velocity is increased, the kinetic energy must also increase. This means that the kinetic energy for the roller coaster system is greatest at the bottom of the highest hill on the track

57. When a swing moves back and forth, kinetic and potential energy are constantly changing.
However, Mechanical energy stays constant.
No energy is destroyed

58. The Law of Conservation of Energy
Energy can change from on form to another, but the total amount of energy never changes.
ENERGY IS NEVER DESTROYED!!
(Energy is conserved)

59. The Law of Conservation of Energy is a universal principle that describes what happens to energy as it is transferred from one object to another or as it is transformed.

60. Sometimes it is hard to see the Law of Conservation at work
How about when you are on a bike or skiing, what happens to the kinetic energy of your movement?

61. Converting Mass into Energy
How does the Sun unleash enough energy to light and warm Earth from so far away?
A special kind of energy conversion – Nuclear Fusion
- A small amount of mass is transformed into a tremendous amount of energy.

62. Nuclear Fission
Another process involving the nuclei of atoms is called – Nuclear Fission.
In this process nuclei are broken apart.
In both of these process mass is converted to energy
Nuclear Fission is used by nuclear power plants to generate electrical energy.

63. What forms of energy that we have talked about can you find in the human body?
When you move you convert CPE into Kinetic Energy.
Some of the CPE is transformed into Thermal Energy

64. The complex process that go on in your body also obey the
Law of Conservation of Energy.
Your body stores energy as CPE.
This CPE is used to fuel the processes that keep you alive,
-making your heart beat
Digesting the food you eat
Converting it to heat
Helping you move

65. To maintain a healthy weight you much have a proper balance between energy contained in the food you eat and the energy your body uses.

66. Food Energy
The food Calorie © is a unit used by nutritionists to measure how much energy you get from various foods.
1 C = about 4,184 J
Every gram of fat a person consumes can supply 9 C of energy.

67. Answer : B
An 80 kg skater falls from a 10 m high railing. What is the GPE of the skater halfway down.
A J
B J
C J

68. Answer : C
What is the Mechanical energy of a 500 kg rollercoaster car moving with a speed of 3 m/s at the top of a hill that is 30 m high.
2250 J
147,000 J
149,250 J

69. Answer : C
__________ is energy stored by things that stretch or compress.
A) Elastic kinetic energy
B) Gravitational potential
C) Elastic potential energy
D) Chemical kinetic energy

70. Answer : A Energy stored in chemical bonds is __________.
A) chemical potential energy
B) chemical kinetic energy
C) energy of activation
D) thermal potential energy

71. Answer : D
How much gravitational potential energy does a 75-kg diver have stepping off the edge of a 5-m platform?
A) 375 J
B) 15 J
C) 147 J
D) 3,675 J

72. Answer : C
How much kinetic energy does a moving object have if its mass is 100 kg and it is moving at a speed of 5 meters per second?
A) 2,500 J
B) 250 J
C) 1,250 J
D) 125,000 J

73. Answer : C
A baseball is hit into the air with a bat. When does the baseball have the greatest gravitational potential energy?
A) when it reaches its highest point
B) when it leaves the bat
C) when it hits the ground
D) when the mechanical and kinetic energies of the baseball are equal