1. Potential and Kinetic Energy

2. What does it mean if you have a lot of energy?
For students it means you can run around, lift weights and talk.

3. 1. What is Energy?
If you have energy you have the ability to do work

4. 2. How is all energy divided?
Potential
Energy
Kinetic
Energy
Gravitation
Potential
Energy
Elastic
Chemical

5. 3. What is Potential Energy?
Energy that is stored and waiting to be used later

6. 4. What is Gravitational Potential Energy?
Potential energy due to an object’s position
Formula = P.E. = m x h x g

7. Potential Energy PE = mgh m = mass g = acceleration due to gravity
h = height
Units: Joules (J)

8. 5. Examples of gravitational potential energy
A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.

9. Gravitational Potential Energy
If you stand on a 3- meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.

10. Gravitational Potential Energy
“The bigger they are the harder they fall” is not just a saying. It’s true.
Objects with more mass have greater G.P.E.
The formula to find G.P.E. is
G.P.E. = Mass X Weight X Height.

11. 7. Let’s Practice
A rock has a mass of 8.40 kg. The center of mass is 29.0 m above the ground. How much energy does it have?
PE = mgh
We know:
m= 8.40 kg
g= 9.8 m/s2
h= 29.0 m
PE = (8.4)(9.81)(29)
= J

12. 8. What is Elastic Potential Energy?
Potential energy due to compression or expansion of an elastic object.
Notice the ball compressing
and expanding

13. 9. What is Chemical Potential Energy?
Potential energy stored within the chemical bonds of an object

14. STOP – Your turn to practice!
15 minutes of practice on your own and then we will learn about the other category of energy…

15. How is kinetic different from potential?
KINETIC ENERGY
Energy of motion
How is kinetic different from potential?

16. 1. What is Kinetic Energy? 2. What is the formula?
the energy of motion
2. What is the formula?
KE = ½ mv2
Units: Joules (J)
m = mass
v = velocity
3. What is the unit?
Joule

17. 4. The faster an object moves, the more kinetic energy it has.
The greater the mass of a moving object, the more kinetic energy it has.
Kinetic energy depends on both mass and velocity.

18. Math Skills
What is the kinetic energy of this car when it is traveling 38.0 m/s?
What other information do you need?
KE = ½ m v2
= ½ (1550)(38.0)^2
= J
= 1.11 x 10^6 J
Car’s mass = 1550kg

19. STOP! You practice!

20. After the Lesson:
You will be able to identify and describe conversions from one type of energy to another.
You will be able state the law of conservation of energy.
In this lesson, students will learn the definitions of both potential and kinetic energy. They will also be able to give examples of each and explain how potential energy changes into kinetic energy.

21. Energy: Forms and Changes

23. Nature of Energy Energy is all around you!
You can hear energy as sound.
You can see energy as light.
And you can feel it as wind.

24. Nature of Energy You use energy when you: hit a softball.
lift your book bag.
compress a spring.

25. Living organisms need energy for growth and movement.
Nature of Energy
Living organisms need energy for growth and movement.

26. Nature of Energy Energy is involved when: a bird flies.
a bomb explodes.
rain falls from the sky.
electricity flows in a wire.

27. Nature of Energy Energy can be defined as the ability to do work.
What is energy that it can be involved in so many different activities?
Energy can be defined as the ability to do work.
If an object or organism does work (exerts a force over a distance to move an object) the object or organism uses energy.

28. Nature of Energy
Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J).
In addition to using energy to do work, objects gain energy because work is being done on them.

29. Forms of Energy Heat (Thermal) Chemical (food, fire, …)
The five main forms of energy are:
Heat (Thermal)
Chemical (food, fire, …)
Electromagnetic (electricity and magnetism)
Nuclear (nuclear power, atomic bomb)
Mechanical (motion and position of objects)

30. Heat Energy or Thermal Energy
The internal motion of the atoms is called heat energy, because moving particles (kinetic energy) produce heat.
Heat energy can be produced by friction.
Heat energy causes changes in temperature and phase of any form of matter.
As an object moves faster, it increases its thermal energy.

31. Chemical Energy Chemical Energy is required to bond atoms together.
And when bonds are broken, energy is released.
Fuel and food are forms of stored chemical energy.

32. Electromagnetic Energy
Electromagnetic energy is a form of energy that travels through space in the form of waves.
Power lines carry electromagnetic energy into your home in the form of electricity.

33. Electromagnetic Energy
Light is a form of electromagnetic energy.
Each color of light (Roy G Biv) represents a different amount of electromagnetic energy.
Electromagnetic Energy is also carried by X-rays, radio waves, and laser light.

34. Nuclear Energy
The nucleus of an atom is the source of nuclear energy.

35. Nuclear Energy
When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy.

36. Nuclear Energy
The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei.
Nuclear energy is also released when nuclei collide at high speeds and join (fusion).

37. Mechanical Energy
Mechanical energy is the energy associated with the motion and position of everyday objects.
When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy.

38. Mechanical Energy
When you throw a balling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins (transfer of momentum).
When you kick a football, you give mechanical energy to the football to make it move.

39. Mechanical Energy
Mechanical energy is the sum of an object’s potential energy and kinetic energy.
Mechanical Energy = Potential Energy + Kinetic Energy

40. The Law of Conservation of Energy states that energy can not be created or destroyed, but may change from one form to another.
Therefore, the total amount of energy in the universe is constant.

41. Law of Conservation of Energy
In 1905, Albert Einstein said that mass and energy can be converted into each other.
He showed that if matter is destroyed, energy is created, and if energy is destroyed mass is created.
E = MC2
Energy = Mass X Speed of Light2

42. Example:
A bouncing ball will continually alternate between kinetic and potential energy as it goes up and down. (Changing from one form of energy to another.)

43. Explain what happens to the kinetic, potential, and mechanical energies of a pendulum as it swings back and forth.

44. Kinetic-Potential Energy Conversion
Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

45. Kinetic vs. Potential Energy
At the point of maximum potential energy, the car has minimum kinetic energy.

46. Kinetic-Potential Energy Conversions
As a basketball player throws the ball into the air, various energy conversions take place.

47. Ball slows down
Ball speeds up

48. Conceptual understanding
A penny is dropped off the Eiffel tower (ignore air resistance). As it falls, what happens to it’s potential energy? What happens to it’s kinetic energy?
As it falls, its velocity goes up, so its kinetic energy goes up. It also looses height so its potential energy goes down.
However, mechanical energy stays the same ME = KE + PE

49. Definition of Energy Conversion
The change from one form of energy to another.
In order to understand the different forms of energy, you have to know what the term “energy” means. Energy is the ability or the capacity of an object to do work. This is measured in two different ways : capability of doing work- known as potential energy, and the conversion of the capability to motion- called kinetic energy.

50. Energy Conversion
Energy can be changed from one form to another. Changes in the form of energy are called energy conversions.
If energy seems to disappear, then scientists look for it – leading to many important discoveries.

51. Conservation of Energy
If you set a spinning top in motion, will the top remain in motion forever?
No, it will not.
Then what happens to its energy?
Is the energy destroyed?
Again, the answer is no.

52. Energy and Friction
So what happens to the energy of the top in the Figure?
As the top spins, it encounters friction with the floor and friction from the air.
Whenever a moving object experiences friction, some of its kinetic energy is transformed into thermal energy.
So, the mechanical energy of the spinning top is transformed to thermal energy.
The top slows and eventually falls on its side, but its energy is not destroyed—it is transformed.

53. According to the law of conservation of energy, energy cannot be created or destroyed.
So the total amount of energy is the same before and after any transformation.
If you add up all the new forms of energy after a transformation, all of the original energy will be accounted for.

54. Sometimes energy might seem to be lost, like the bouncing ball gradually coming to a stop, or the pendulum gradually stopping. This energy is not actually lost, it is just transferred into a different form, such as thermal energy (heat).

55. An automobile engine takes gasoline (chemical potential energy) and burns it (thermal energy) and uses the gases from the burning to turn drive pistons which turn the axles (kinetic energy).

56. Energy Conversion in a Waterfall
There is a conversion between potential and kinetic energy on a large scale at Niagara Falls.
The water at the top of the falls has gravitational potential energy because it is higher than the bottom of the falls.
But as the water falls, its height decreases and so it loses potential energy.
At the same time, its kinetic energy increases because its velocity increases.
Thus potential energy is converted into kinetic energy.

57. Series of Conversions-1
Often a series of energy conversions is needed to do a task.
For example, Strike a match:
The mechanical energy used to scratch the match is converted to thermal energy.
The thermal energy causes the match to release stored chemical energy
The chemical energy is then converted to thermal energy and to the energy you see as light.

58. Series of Conversions-2
In a car engine another series of conversions occurs.
Electrical energy produces a hot spark.
The thermal energy of the spark releases chemical energy in the fuel.
When the fuel burns, this chemical energy in turn becomes thermal energy.
Thermal energy is converted to mechanical energy used to move the car, and to electrical energy that produces more sparks.

59. Energy conversions
All forms of energy can be converted into other forms.
The sun’s energy through solar cells can be converted directly into electricity.
Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy).

60. Other energy conversions
In an electric motor, electromagnetic energy is converted to mechanical energy.
In a battery, chemical energy is converted into electromagnetic energy.
The mechanical energy of a waterfall is converted to electrical energy in a generator.