Kinetic Energy

Kinetic Energy

Middle School

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Learning Objectives

• Define kinetic energy and its relationship to an object's mass and speed.

• Explain that temperature measures the average kinetic energy of particles in a substance.

• Describe how thermal energy changes particle motion, temperature, and causes changes of state.

• Explain how particle motion leads to thermal expansion, contraction, and changes in pressure.

Key Vocabulary

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Kinetic Energy

Kinetic energy is the energy that an object possesses because of its motion.

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Temperature

Temperature is a measure of the average kinetic energy of the particles in a substance.

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Thermal Energy

Thermal energy represents the total kinetic energy of all the individual particles in a substance.

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Pressure

Pressure is the amount of force exerted by gas particles colliding with a surface.

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Matter

Matter is anything in the universe that has both mass and takes up space.

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Expansion

Expansion describes the increase in the volume or size of a substance when heated.

Key Vocabulary

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Contraction

This is the decrease in the volume or size of a substance when it is cooled.

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Gas

A state of matter where particles are spread out and move freely in all directions.

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Liquid

A state of matter where particles are close together but can slide past one another.

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Solid

A state of matter where particles are tightly packed and only vibrate in a fixed position.

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What Is Kinetic Energy?

• Air is matter; its gas particles have mass and are in constant motion.

• Kinetic energy is the energy of motion in an object or particle.

• The amount of kinetic energy depends on an object’s mass and speed.

• Heating particles increases their speed and therefore their overall kinetic energy.

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Multiple Choice

What is kinetic energy?

• The energy stored in chemical bonds

• The energy of motion in an object or particle

• The energy from the position of an object

• The energy created by heat

Multiple Choice

What is the relationship between heating air and the kinetic energy of its particles?

• The kinetic energy increases because the particles get larger.

• The kinetic energy decreases because the particles slow down.

• The kinetic energy increases because the particles move faster.

• The kinetic energy stays the same because air has no mass.

Multiple Choice

A large truck and a small car are both traveling at the same speed. Which statement best explains their kinetic energy?

• The car has more kinetic energy because it is smaller.

• The truck has more kinetic energy because it has more mass.

• They have the same kinetic energy because their speed is the same.

• Only the car has kinetic energy because the truck is too heavy.

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Temperature vs. Thermal Energy

Cup of Hot Tea

• ​The hot tea has a high temperature, meaning its particles have a high average kinetic energy.

• ​​The individual particles in the tea are moving very rapidly, much faster than in cool water.

• ​However, it has less thermal energy because there are far fewer particles than in the bathtub.

Bathtub of Cool Water

• ​The cool water has a low temperature, meaning its particles have a low average kinetic energy.

• ​​The individual particles in the water are moving much more slowly than in the hot tea.

• ​However, it has more thermal energy because it contains a vastly larger number of particles.

Multiple Choice

What does the temperature of a substance directly measure?

• The average kinetic energy of its particles.

• The total number of particles in the substance.

• The total kinetic energy of all its particles.

• The size of the individual particles.

Multiple Choice

Why does a bathtub full of cool water have more thermal energy than a small cup of hot tea?

• Its particles are moving much more rapidly.

• It contains a vastly larger number of particles.

• The water is at a much higher temperature.

• Its particles have a higher average kinetic energy.

Multiple Choice

A small candle flame has a very high temperature, while a large iceberg has a very low temperature. Which statement accurately compares their thermal energy?

• The candle flame has more thermal energy because it has a much higher temperature.

• The iceberg has more thermal energy because it is made of vastly more particles.

• They have the same amount of thermal energy because of their differences in size and temperature.

• The iceberg has no thermal energy because its particles are not moving.

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Expansion and Contraction

Expansion

• Adding thermal energy to a substance increases the kinetic energy of its particles.

• This increased energy causes the particles to move farther apart, making the matter expand.

• The size of individual particles does not change, only the space between them.

Contraction

• When matter cools, its particles lose kinetic energy and move more slowly.

• The particles move closer together, causing the substance to contract or shrink.

• Bridges use expansion joints to prevent damage from expansion and contraction.

Multiple Choice

What happens to the particles of a substance that causes it to expand when thermal energy is added?

• The particles of the substance get bigger in size.

• The particles of the substance move farther apart.

• The particles of the substance begin to melt.

• The particles of the substance lose their kinetic energy.

Multiple Choice

What is the cause-and-effect relationship that explains why a substance contracts when it cools?

• Its particles get smaller in size, causing the substance to shrink.

• Its particles gain kinetic energy and start to move faster.

• Its particles lose kinetic energy and move closer together.

• Its particles stop moving completely when the substance cools.

Multiple Choice

Based on the concepts of expansion and contraction, what is the most likely reason bridges are built with expansion joints?

• To make the bridge heavier and more stable against wind.

• To allow the bridge materials to expand and contract without causing damage.

• To help the bridge's particles increase or decrease in size.

• To cool the bridge down on hot days to prevent it from melting.

Energy and Phase Changes

• Adding thermal energy can cause a change of state.

• Temperature remains constant during a phase change.

• Removing thermal energy also causes phase changes.

Multiple Choice

What is the primary role of thermal energy in relation to phase changes?

• It can be added or removed to cause a substance to change state.

• It only causes substances to become hotter.

• It only causes substances to become colder.

• It has no effect on the state of a substance.

Multiple Choice

What happens to the temperature of a substance while it is actively undergoing a phase change?

• It increases rapidly.

• It decreases rapidly.

• It remains the same.

• It fluctuates up and down.

Multiple Choice

If you are heating a substance and its temperature stops rising for a period of time, what is the most likely conclusion?

• The substance is not actually absorbing any energy.

• The thermometer is likely broken.

• The added energy is being used to change the state of the substance.

• The temperature will only change if energy is removed.

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Kinetic Energy and Gas Pressure

• Gas pressure is the force from particles hitting the container's walls.

• When a gas is heated, its particles gain kinetic energy and move faster.

• This causes more frequent and forceful collisions, which increases the gas pressure.

• If a gas is cooled, its particles slow down, causing pressure to decrease.

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Multiple Choice

What is gas pressure?

• The force from particles hitting the walls of a container.

• The total weight of all the gas particles.

• The amount of space between gas particles.

• The chemical energy stored in gas particles.

Multiple Choice

Why does heating a gas in a sealed container increase the pressure?

• The particles get larger and take up more space.

• The particles move faster and have more frequent and forceful collisions.

• The particles stick to the walls of the container.

• The number of particles in the container increases.

Multiple Choice

If a sealed container of gas is moved from a warm room into a cold freezer, what is the most likely outcome?

• The pressure will increase because the container is now colder.

• The pressure will decrease because the gas particles will slow down.

• The pressure will stay the same because the container is sealed.

• The pressure will decrease because the particles will get smaller.

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Common Misconceptions

Misconception	Correction
Heating a substance makes its particles get bigger.	Particles stay the same size. Heating increases their kinetic energy, causing them to move apart.
Temperature and thermal energy are the same thing.	Temperature is the average kinetic energy of particles; thermal energy is the total energy.
Air is empty space and has no mass.	Air is matter. Its particles have mass and are in constant, random motion.

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Summary

• Temperature measures the average kinetic energy of an object's moving particles.

• Thermal energy is the total kinetic energy of all particles in a substance.

• Adding thermal energy can cause expansion, a rise in pressure, or a change of state.

• Temperature remains constant during a phase change as energy changes the substance's state.

Poll

On a scale of 1-4, how confident are you about explaining the difference between temperature and thermal energy?

• 1

• 2

• 3

• 4