Kinetic and Potential Energy

Kinetic and Potential Energy

Middle School

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Learning Objectives

• Define kinetic and potential energy and explain the main differences between them.

• Explain the law of conservation of energy and how energy changes its form.

• Identify different forms of potential energy, like gravitational and elastic.

• Understand the relationship between work, force, and energy.

Key Vocabulary

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Potential Energy

Energy that is stored in an object or system and is ready to be used.

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Kinetic Energy

The energy associated with an object in motion, or the vibration of its atoms or molecules.

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Work

A force is said to be doing work if it is exerted over a distance to move an object.

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Power

The rate at which work is done by a system or object over a period of time.

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Conservative Forces

A force where the work done to move an object between two points is independent of the path taken.

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Non-Conservative Forces

A force where the work done to move an object between two points depends on the path taken.

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Energy Is the Ability to Do Work

Potential Energy

• Potential energy is the stored energy in an object due to its position or shape.

• This energy is waiting to be used and is not currently causing any motion.

• A diver on a high board has potential energy from their height above the water.

Kinetic Energy

• Kinetic energy is the energy that an object has because it is in motion.

• The faster an object is moving, the more kinetic energy it will have.

• As a diver falls, their potential energy changes into the kinetic energy of motion.

Multiple Choice

A bird is sitting on a tree branch. What type of energy does it primarily have due to its position?

• Work Energy

• Potential Energy

• Motion Energy

• Kinetic Energy

Forms of Potential Energy

• Potential energy is stored energy an object has because of its position or condition.

• It increases when an object is lifted higher above the ground or when it is stretched or compressed.

• It is also stored in the chemical bonds of materials like food and fuel.

Multiple Choice

Which of the following is an example of an object with elastic potential energy?

• A stretched bowstring

• A book on a high shelf

• A moving car

• A battery

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What Is the Law of Conservation of Energy?

• Energy can never be created or destroyed, only change forms.

• ​Seemingly lost energy often turns into heat or sound energy.

• A rising cannonball converts kinetic energy to potential energy.

• A falling cannonball converts potential energy back to kinetic energy.

Multiple Choice

According to the law of conservation of energy, what happens when a cannonball falls from its highest point?

• Energy is destroyed.

• Potential energy is converted into kinetic energy.

• New energy is created.

• Kinetic energy is converted into potential energy.

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Work, Power, and the Work-Energy Theorem

Work

Power

Multiple Choice

What does the work-energy theorem state?

• Work is only done by conservative forces.

• Work is the total energy of an object.

• The work done on an object equals the change in its kinetic energy.

• Power is the same as work.

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Common Misconceptions

Misconception	Correction
Energy can be 'lost' or used up.	Energy is never destroyed; it simply transforms into other forms.
An object at rest has no energy.	Objects at rest can have potential energy.
Applying a force always does work.	Work is only done if the force causes the object to move.

Multiple Choice

If a 5 kg ball and a 10 kg ball are both lifted to the same height, how does the gravitational potential energy of the 10 kg ball compare to the 5 kg ball?

• It is the same.

• It is half.

• It is four times greater.

• It is double.

Multiple Choice

A roller coaster car is at the top of a hill, motionless. As it starts to roll down the hill, how do its potential and kinetic energy change?

• Potential energy decreases, and kinetic energy increases.

• Both potential and kinetic energy increase.

• Both potential and kinetic energy decrease.

• Potential energy increases, and kinetic energy decreases.

Multiple Choice

A construction worker lifts a 10kg box from the ground to a shelf 2 meters high. He then slides it 3 meters horizontally along the shelf. At which stage was work done against gravity?

• During both the lift and the slide.

• Only when lifting the box vertically.

• Only when sliding the box horizontally.

• No work was done at all.

Multiple Choice

Imagine a pendulum swinging. If air resistance (a non-conservative force) is present, what will happen to the total mechanical energy (potential + kinetic) of the pendulum over time?

• The total energy will remain constant.

• The total energy will increase as it gains energy from the air.

• The potential energy will be destroyed.

• The total energy will gradually decrease as it transforms into heat.

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Summary

Poll

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

• 1

• 2

• 3

• 4