Chapters 3 & 4

Objectives

• Recognize how energy causes change.

• Describe common forms of energy.

• Illustrate that the two general types of energy are kinetic energy and potential energy.

Different Forms of Energy Have Different Uses

• Energy takes on many forms.

• Lamps use electrical energy while plants use energy from the sun to grow.

Energy

• All forms of energy have one important point in common--- they cause change to occur.

• The flow of electrical energy through a wire causes a cool, dark bulb to get hot and glow.

• You are a source of energy that makes changes in your environment!

What in this picture is using energy?

Forms of Energy

• Mechanical Energy

• Sound Energy

• Chemical Energy

• Thermal Energy

• Electromagnetic Energy

• Nuclear Energy

Mechanical Energy

• Energy that moves objects is mechanical energy.

• The energy that you use to put book on a shelf is mechanical energy, s is energy that a person uses to turn car key.

Sound Energy

• Vibrations of particles• When you hear a car

drive by, you are detecting vibrations in the air produced by sound energy.

• Cannot travel through empty space.

Chemical Energy

• Energy that is stored in chemical compositions of matter.

• Example: When wood or gasoline burns, chemical energy produces heat.

• The energy used by your body cells comes from chemical energy.

Thermal Energy

• The total amount of energy from the movement of particles in matter is thermal energy.

• The energy of this motion in an object is the object’s thermal energy.

Electromagnetic Energy

• Transmitted through space in the form of electromagnetic waves.

• Include visible light, x-rays, and microwaves.

• The sun releases a large amount of electromagnetic energy, some of which is absorbed by Earth.

Nuclear Energy

• The center of an atom– it’s nucleus– is the source of nuclear energy.

• When a heavy atom’s nucleus breaks apart or when the nuclei of two small atoms join together, energy is released.

Nuclear Energy

• Everything has a beginning, and nuclear energy is no exception. The first reactor to use nuclear energy was built in 1942. The discovery of fission, that lead to nuclear energy, was discovered a few years earlier. A man named Enrico Fermi first discovered fission. In 1934, Fermi proved that neutrons could split atoms. This was breaking news. The particles made by these splits were lighter than the original atom. Later the scientist added up the particles, and still it weighed less than the original product. This proved that Einstein's theory was right, that some of the mass changed to energy. This theory was none other than e=mc2. The uses of this energy would be great. From cities, to ships, to bombs, nuclear energy powers them all.

Kinetic Energy

• The energy of motion is called Kinetic energy.

• Kinetic energy increases as mass increases.– For example is a bowling ball and a soccor

ball were moving at the same speed, the bowling ball would have more kinetic energy because of its greater mass.

Kinetic Energy

• Kinetic energy increases as speed increases.– If two identical bowling balls were rolling along

at different speeds, the faster one would have more kinetic energy because of its greater speed.

Potential Energy

• Potential Energy is the stored energy that an object has due to its position or chemical composition.

• P. 75-76

Review

• Give three ways you use energy. How does each example involve a change?

• What two factors determine an object’s kinetic energy?

How can potential energy be changed into useful forms of

energy?

Energy can change forms but is NEVER Lost!

• Potential energy is stored in the chemicals on the head of a match. The flame of a burning match releases that energy as light and heat. Where does the energy to strike the match come from in the first place.

Energy Changes Forms

• Matches chemical energy stored can be changed to light and heat.

• Photosynthesis

• Page 78

Conversions between Potential Energy and Kinetic Energy

• Potential energy can be changed into kinetic energy and back into potential energy.

• Page 79

Using Energy Conversions

• Page 80-81

Energy is Always Conserved

• As the soccer ball rolls, it rubs against the ground. Some kinetic energy changes into heat because of friction.

• Some of the ball’s energy changes to sound energy as you hear the ball roll.

• Although the ball loses kinetic energy, the overall amount of energy in the universe does not decrease.

Energy is Always Conserved

• In the soccer ball, the ball loses energy, but this energy is transferred to other parts of the universe. Energy is conserved.

• The Law of Conservation of Energy- states that energy can neither be created nor destroyed.

• Balance of Energy

Energy Conversions may produce unwanted forms of energy

• When energy changes forms, the total amount of energy is conserved.

• However, the amount of useful energy is almost always less than the total amount of energy.

Energy Efficiency

• Energy Efficiency is a measurement of usable energy after an energy conversion.

• Example: Energy-efficient house-hold appliances. These appliances convert a greater percentage of energy into the desired form than inefficient forms.

Review

• Describe an energy conversion you have observed in your own life.

• What is the Law of Conservation of Energy?

• Give an example of an energy conversion that produces unwanted forms of energy.