Unit 3 pp #6 7th grade

Chapter 19

Kinetic and Potential Energy Conversions

• An energy conversion is a change from one form of energy to another.

• Any form of energy can change into any other form.

• Often, one form of energy changes into more than one other form.

Section 3 Energy Conversion and Transfer

Chapter 19

Kinetic and Potential Energy Conversions, continued

• As a skateboarder moves at high speed up a half pipe, he has a lot of kinetic energy.

• At the top of the half pipe, he hangs in the air. All his kinetic energy has changed to potential energy.

• As he zips down the side, his potential energy has become kinetic again.


Section 3 Energy Conversion and TransferChapter 19

Chapter 19

• Energy Conversions in a Rubber Band The wound-up rubber band in a toy airplane has stored potential energy.

• When the rubber band is let go, the stored energy becomes kinetic energy, spins the propeller, and makes the airplane fly.



Chapter 19

• The energy you use to stretch a rubber band is converted to potential energy.

• The potential energy in the rubber band is similar to the potential energy of the skateboarder at the top of the half pipe.

• When you let the rubber band go, it snaps back and releases its stored potential energy.



Chapter 19

Conversions Involving Chemical Energy

• Your body uses chemical energy to function.

• That chemical energy comes from the food you eat.

• Some of the chemical energy of food is converted to kinetic energy when you are active. Some of it is converted into thermal energy to maintain your body temperature.


Chapter 19

Conversions Involving Chemical Energy, continued

• Energy Conversions in Plants Chemical energy in food comes from the sun’s energy.

• Plants use photosynthesis and light energy from the sun to make new substances that have chemical energy.

• When you eat fruits, vegetables, or grains, you are taking in chemical energy converted from the sun’s energy.


Chapter 19

• When you eat meat from animals that ate plants, you are also taking in energy that first came from the sun.

• The chemical energy stored in plants can also be converted to other forms of energy.

• Burning wood from a tree converts chemical energy into thermal energy.



Chapter 19

• Continuation of the Process Let’s trace where the energy goes.

• Plants change light energy into chemical energy.

• The chemical energy in food you eat is changed into another chemical energy your body can use.



Chapter 19

• Your body then uses that chemical energy to give you the kinetic energy that you use in everything you do.

• The process is endless—energy is always going somewhere.



Chapter 19

Energy Conversions and Friction• Roller coasters have a mechanism that pulls the

cars up to the top of the first hill.

• Then the cars are released. Potential energy is turned into kinetic energy, and back into potential energy as they go up and down hills.

• But the cars never return to their original height.


Chapter 19

Energy Conversions and Friction, continued

• Energy is not lost—it is converted to other forms.

• Friction and Thermal Energy On a roller coaster, there is friction between the cars’ wheels and the track, and between the cars and the air around them.

• Friction is a force that opposes motion between two surfaces that are touching.


Chapter 19

Energy Conversions and Friction, continued

• Because of friction, some energy is always converted to thermal energy.

• As a result, not all of the potential energy of the cars changes into kinetic energy as the cars go down the first hill.

• Likewise, not all of the kinetic energy of the cars changes back into potential energy.


Chapter 19

Energy in a Closed System

• A closed system is a group of objects that transfer energy only to each other.

• The closed system of a roller coaster consists of the track, the cars, and the air around them.

• On a roller coaster, some mechanical energy (the sum of kinetic and potential energy) is always converted into thermal energy because of friction.


Chapter 19

Energy in a Closed System, continued• Sound energy also comes from the energy

conversions of a roller coaster.

• If you combine the kinetic energy at the bottom of the first hill, thermal energy due to friction, and sound energy, the total amount is the same as the original amount of potential energy.

• So energy is conserved and not lost.


Chapter 19

Energy in a Closed System, continued• The law of conservation of energy states that

energy cannot be created or destroyed.

• The total amount of energy in a closed system is always the same.

• Energy can change from one form to another, but all the different forms always equal the same total.


Chapter 19

Energy Transfers

• In all energy transfers, some useful energy is converted to less-usable energy, and the disorder of the system increases.

• Increased disorder means that energy is converted to other forms, causing changes in the system or its surroundings.

• Most events, such as weather changes, moving cars, and nerve impulses, involve some form of energy transfer.


Chapter 19

Energy Transfers, continued

• The energy transfers involved in weather have many forms.

• Thermal energy from the sun evaporates water on Earth. This water forms clouds.

• The water can return to Earth as the gravitational potential energy of the water in the clouds is converted to the kinetic energy of falling water drops, or rain.


Chapter 19


• A hurricane is a dramatic form of weather-related energy transfer.

• The energy of warm ocean waters allows the formation of vast storms that may become hurricanes.

• The kinetic energy of hurricane winds can cause loss of life and billions of dollars of damage.


Chapter 19


• Energy Transfers and Moving Cars The next slide shows how the chemical energy of gasoline undergoes energy transfers to move a car.

• Not all of the gasoline’s energy makes a car move.

• In every energy transfer, some of the original energy is lost to the surroundings as thermal energy.


Chapter 19


• Energy Transfers and Nerve Impulses Energy is involved in human reflex actions.

• If you step on a sharp object, pain receptors on the bottom of your foot trigger chemical reactions.

• The chemical energy released in these reactions is converted to electrical energy.


Chapter 19


• This electrical energy is sent as impulses to the spinal cord and then through nerves to the muscles in your leg and foot.

• The impulses cause chemical energy to convert into kinetic energy to lift your foot.

• Amazingly, the reflex happens even faster than the electrical impulses can travel through your nerves to your brain.


Unit 3 pp #6 7th grade

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Transcript of Unit 3 pp #6 7th grade