Law of Conservation of Energy

Law of Conservation of Energy

Middle School

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Learning Objectives

• Define the Law of Conservation of Energy.

• Differentiate between potential energy and kinetic energy.

• Describe how energy can be transferred from one form to another.

• Identify real-world examples of energy transformation.

Key Vocabulary

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Conservation of Energy

The law stating that energy cannot be created or destroyed, only changed from one form to another.

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Potential Energy

This is the stored energy an object possesses due to its position or state, ready for use.

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Kinetic Energy

This is the energy an object possesses because of its motion, which depends on its mass.

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Photosynthesis

The process where green plants use sunlight to convert light energy into chemical energy to produce food.

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What is the Law of Conservation of Energy?

• Energy cannot be created or destroyed; it only changes from one form to another.

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

• No energy transfer is 100% efficient because some energy is always lost, usually as heat or sound.

• Potential energy is stored energy, like a coaster at the top of a hill.

• Kinetic energy is the energy of motion, like a coaster speeding down a hill.

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Multiple Choice

According to the Law of Conservation of Energy, what is true about the total amount of energy in a system?

• It can increase if energy is created.

• It can decrease if energy is destroyed.

• It always remains the same, though it can change form.

• It is equal to the amount of potential energy only.

Energy Transformation in Action

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Mechanical Systems

• Energy converts between potential and kinetic in a moving roller coaster.

• At the highest point, its potential energy is at the maximum.

• As the coaster moves faster, this becomes kinetic energy.

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Biological Systems

• Plants use photosynthesis to transform light energy from the sun.

• This changes light energy into stored chemical energy as food.

• This shows how energy changes its form in the natural world.

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Technological Systems

• Your phone's battery contains stored chemical energy for you to use.

• When used, this energy becomes the light of the screen.

• It also transforms into sound energy from the phone's speakers.

Multiple Choice

When a person jumps on a trampoline, what energy transformation occurs as they move downwards after reaching the highest point?

• Kinetic energy is converted to potential energy.

• Potential energy is converted to kinetic energy.

• Light energy is converted to chemical energy.

• Chemical energy is converted to sound energy.

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Common Misconceptions

Misconception	Correction
You can create energy.	Energy cannot be created; it only changes form.
Energy is “used up” and disappears.	Energy does not disappear; it transforms into other forms, like heat.
An object at rest has no energy.	An object can have stored potential energy when it is not moving.

Multiple Choice

Why is it incorrect to say that a phone battery 'runs out' of energy?

• Because the energy is destroyed by the phone.

• Because the battery's stored chemical energy has been transformed into other forms, like light and heat.

• Because the energy leaks out of the phone.

• Because the energy is returned to the electrical grid.

Multiple Choice

A girl throws a ball into the air. When does the ball have the most potential energy?

• Just after it leaves her hand.

• When it is halfway to the top.

• At the highest point of its flight.

• Just before it is caught.

Multiple Choice

A power plant burns coal to generate electricity. Which statement best describes the energy transformation based on the Law of Conservation of Energy?

• Energy is created from the coal.

• Electricity is a form of matter, not energy.

• The chemical energy in coal is converted into thermal and then electrical energy.

• The process destroys the energy stored in the coal.

Multiple Choice

If you are told that a machine is 100% efficient, what does this imply about energy transformation?

• The machine creates its own energy.

• All the input energy is successfully converted into the desired form of output energy without any being changed to heat or sound.

• The machine destroys a small amount of energy.

• The Law of Conservation of Energy does not apply to machines.

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Summary

• The Law of Conservation of Energy states that energy is never created or destroyed.

• Energy is constantly transforming, for example from potential to kinetic energy.

• The total energy in an isolated system always remains constant as it changes form.

• Roller coasters, photosynthesis, and batteries all demonstrate energy conservation.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

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• 4