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# Unit 3 pp #6 7th grade

## by tarinakline on Oct 20, 2010

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## Unit 3 pp #6 7th gradePresentation Transcript

• Section 3 Energy Conversion and Transfer
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 Transfer
Chapter 19
• Section 3 Energy Conversion and Transfer
Chapter 19
Kinetic and Potential Energy Conversions, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Kinetic and Potential Energy Conversions, continued
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
• Section 3 Energy Conversion and Transfer
Chapter 19
Conversions Involving Chemical Energy, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Conversions Involving Chemical Energy, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Conversions Involving Chemical Energy, continued
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
• Section 3 Energy Conversion and Transfer
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.
• Section 3 Energy Conversion and 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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Energy Transfers, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Energy Transfers, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
• Section 3 Energy Conversion and Transfer
Chapter 19
Energy Transfers, continued
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.
• Section 3 Energy Conversion and Transfer
Chapter 19
Energy Transfers, continued
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.