Bellringer

Finish the following sentence:“Energy is the ability to ____.”

Write your completed sentence in your science journal. People often use the words energy and power synonymously, but they have specific meanings. What is the distinction between energy and power?

Energy and Work: Working Together

• Energy is the ability to do work.

• Work is done when a force causes an object to move in the direction of the force. Work is a transfer of energy.

• Energy and work are expressed in units of joules (J).

Kinetic Energy

• Kinetic energy is the energy of motion. All moving objects have kinetic energy.

• Kinetic Energy Depends on Mass and Speed If you know an object’s mass (m) and its speed (v), you can calculate the object’s kinetic energy with the following equation:

kinetic energy mv 2

2

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Potential Energy

• Potential energy is the energy an object has because of its position.

• Gravitational Potential Energy The amount of gravitational potential energy that an object has depends on its weight and its height.

Potential Energy, continued

•The equation to find gravitational potential energy is:

gravitational potential energy weight height

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Mechanical Energy

• Mechanical energy is the total energy of motion and position of an object. Both kinetic energy and potential energy are kinds of mechanical energy.

• The equation to find mechanical energy is:

mechanical energy potential energy kinetic energy

Other Forms of Energy

• Thermal (Heat) Energy is all of the kinetic energy due to random motion of the particles that make up an object.

• Chemical Energy is the energy of a chemical compound that changes as its atoms are rearranged.

• Electrical Energy is the energy of moving electrons.

• Sound Energy is caused by an object’s vibrations.

• Light Energy is produced by the vibrations of electrically charged particles.

• Nuclear Energy is energy that comes from changes in the nucleus of an atom.

Bellringer

What do the following a plant, a Bunsen burner, and a pendulum have in common? What are three other objects that have same common link?

Write your answers in your science journal.

Kinetic Energy and Potential Energy

• An energy conversion is a change from one form of energy to another. Any form of energy can change into any other form of energy.

• As the skateboarder on the next slide travels up and down the half-pipe, his energy changes back and forth between kinetic energy and potential energy.

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Kinetic Energy and Potential Energy, continued

• Elastic Potential Energy Stretching a rubber band stores elastic potential energy in the rubber band.

• When you let the rubber band go, it goes back to its original shape. It releases its stored-up potential energy as it does so.

Conversions Involving Chemical Energy

• Chemical energy is stored in the food you eat. Your body uses this chemical energy to function.

• Energy Conversion in Plants The chemical energy in the food you eat comes from the sun’s energy. Plants use photosynthesis to convert light energy into chemical energy, as shown on the next slide.

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Why Energy Conversions Are Important, continued

• Conversions Involving Electrical Energy Some common energy conversions that involve electrical energy are shown in the table below.

Alarm clock electrical energy light and sound energy

Battery chemical energy electrical energy

Light bulb electrical energy light and thermal energy

Blender electrical energy kinetic and sound energy

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Bellringer

Answer the following questions:

Where does the energy that makes a roller coaster car move come from? Where does the energy go?

What does “All of the energy put into a process still exists somewhere when the process has ended” mean?

Write your answers in your science journal.

Where Does the Energy Go?

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

• For a roller coaster car to move, energy must be used to overcome the friction between the car’s wheels and the track.

• As a result, not all of the car’s potential energy changes into kinetic energy and not all of the car’s kinetic energy changes back into potential energy.

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Energy Is Conserved Within a Closed System

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

• The Law of Conservation of Energy states that energy cannot be created or destroyed.

• The image below shows energy conservation in a light bulb.

No Conversion Without Thermal Energy

• Any time one form of energy is converted into another form, some of the original energy always gets converted into thermal energy.

• The thermal energy due to friction that results from energy conversions is not usually useful energy.

Nonrenewable Resources

• Nonrenewable resources cannot be replaced or are replaced much more slowly than they are used.

• Fossil fuels are nonrenewable energy resources that formed from the remains of organisms that lived long ago. Oil, natural gas, and coal are the most common fossil fuels.

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Nonrenewable Resources, continued

• Electrical Energy from Fossil Fuels Electric generators convert the chemical energy in fossil fuels into electrical energy by the process shown below.

Nonrenewable Resources, continued

• Nuclear Energy Another way to generate electrical energy is to use nuclear energy.

• In a process called nuclear fission, the nucleus of a radioactive atom is split into two smaller nuclei, which releases nuclear energy.

•Because the supply of radioactive elements is limited, nuclear energy is a nonrenewable resource.

Renewable Resources

• Renewable resources are naturally replaced more quickly than they are used.

• Solar Energy Sunlight can be changed into electrical energy through solar cells.

• Solar cells can be used in devices such as calculators. They can also be placed on the roof of a house to provide electrical energy.

Renewable Resources, continued

• Energy from Water The potential energy of water in a reservoir can be changed into kinetic energy as the water flows through a dam.

• In a hydroelectric dam, falling water turns turbines. The turbines are connected to a generator that changes kinetic energy into electrical energy.

Renewable Resources, continued

• Wind Energy The kinetic energy of wind can turn the blades of a windmill or a wind turbine.

• A wind turbine changes the kinetic energy of the air into electrical energy by turning a generator.

Renewable Resources, continued

• Geothermal Energy is thermal energy caused by the heating of Earth’s crust.

•This energy can be converted into electrical energy at geothermal power plants.

• Biomass is organic matter, such as plants, wood, and waste, that can be burned to release energy.

•Some countries depend on biomass for energy.

Bellringer

Predict whether the following sources of energy are renewable or nonrenewable.

sunlight coal windpetroleum nuclear geothermal

Write and explain your predictions in your science journal.

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