Thermal Energy

Thermal Energy

Middle School

​

Learning Objectives

• Define thermal energy, temperature, heat, and describe the three ways heat transfers.

• Analyze how matter, mass, and the environment affect thermal energy transfer.

• Explain how devices can be designed to control thermal energy transfer.

• Explain that a change in kinetic energy means energy was transferred.

Key Vocabulary

​

Thermal Energy

The total kinetic energy of the particles that make up a substance or object.

​

Temperature

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

​

Heat

The transfer of thermal energy from a warmer object to a cooler object.

​

Conduction

The transfer of heat that occurs when particles are in direct contact with each other.

​

Convection

The transfer of heat through the movement of particles in fluids such as liquids or gases.

​

Radiation

The transfer of heat through space in the form of electromagnetic waves, like light.

Key Vocabulary

​

Conductor

A conductor is a type of material that easily allows heat energy to move or pass through it.

​

Insulator

An insulator is a material that slows down or resists the transfer of heat energy from one place to another.

​

Specific Heat

Specific heat is the amount of energy required to raise the temperature of 1 kilogram of a substance by 1 Kelvin.

​

Thermal Expansion

Thermal expansion is the tendency of matter to increase in volume or size when it is heated up by energy.

​

Kinetic Energy

Kinetic energy is the form of energy that an object possesses due to its motion or movement from one place.

​

Reflectivity

Reflectivity measures how effectively a surface can reflect incoming light or other forms of radiant energy instead of absorbing it.

​

​

Thermal Energy, Heat, and Temperature

Low Thermal Energy

• ​Particles in cooler objects have lower kinetic energy and move slowly.

• ​​This results in lower thermal energy and a lower temperature measurement.

• ​Heat flows away from warmer objects and into these cooler objects.

High Thermal Energy

• ​Particles in warmer objects have higher kinetic energy and move much faster.

• ​​This results in higher thermal energy and a higher temperature measurement.

• ​Heat is the energy that transfers from these warmer objects to cooler ones.

Multiple Choice

What is the definition of heat?

• The transfer of energy from a warmer object to a cooler one.

• The measurement of an object's total kinetic energy.

• The speed of an object's fastest-moving particles.

• The energy stored inside an object's particles.

Multiple Choice

What is the relationship between the movement of particles in an object and its temperature?

• The faster the particles move, the higher the object's temperature.

• The slower the particles move, the higher the object's temperature.

• The movement of particles has no effect on an object's temperature.

• Only objects with slow-moving particles have a measurable temperature.

Multiple Choice

If you place a piece of ice into a warm cup of water, which statement best explains what will happen?

• Heat will transfer from the cup to the ice, causing the ice's particles to move faster.

• Heat will transfer from the ice to the cup, causing the cup's particles to move slower.

• The ice's temperature will stay the same because it has low thermal energy.

• The cup's temperature will increase because it is transferring heat to the ice.

Thermal Energy and States of Matter

• Thermal energy depends on the type, state, and amount of matter.

• More mass means more thermal energy at the same temperature.

• During a state change, thermal energy changes but temperature does not.

Multiple Choice

Which factors determine the amount of thermal energy an object has?

• The type, state, and amount of matter

• Only the temperature of the matter

• The color and shape of the matter

• Only the location of the matter

Multiple Choice

If you have two different-sized pots of water at the exact same temperature, which one has more thermal energy?

• The pot with more water, because it has more mass.

• The pot with less water, because it will heat up faster.

• Both pots have the same thermal energy because their temperature is the same.

• It is impossible to know without measuring the exact temperature.

Multiple Choice

An ice cube is placed in a glass of water and begins to melt. Which statement best describes what is happening during the melting process?

• Thermal energy is being added, and the temperature is increasing.

• Thermal energy is being added, but the temperature of the ice-water mixture is not changing.

• Thermal energy is not being added, but the temperature is increasing.

• Both the thermal energy and the temperature are staying the same.

How Heat is Transferred

​

Conduction

• Energy is transferred through direct contact between particles.

• Faster particles collide with slower particles, transferring their energy.

• This is why a metal spoon gets hot in your cocoa.

​

Convection

• Heat moves through fluids, which are liquids or gases.

• Warmer, less dense fluid rises, and cooler, denser fluid sinks.

• This movement creates a circular flow called a convection current.

​

Radiation

• Energy travels in the form of electromagnetic waves.

• Unlike the others, it does not need matter for transfer.

• Darker surfaces absorb more energy, while lighter surfaces reflect it.

Multiple Choice

What are the three ways that heat energy is transferred?

• Conduction, Convection, and Radiation

• Kinetic, Potential, and Chemical

• Solid, Liquid, and Gas

• Reflection, Refraction, and Absorption

Multiple Choice

Why does a metal spoon placed in a cup of hot cocoa become warm?

• Heat is transferred from the hot cocoa to the spoon through direct contact.

• Warm air rises from the cocoa and heats the spoon in a circular current.

• Energy waves travel from the cocoa to heat the spoon.

• The spoon absorbs the dark color of the cocoa, which makes it warm.

Multiple Choice

In a pot of boiling water, the water moves in a circular pattern. At the same time, you can feel warmth on your hands held near the pot without touching it. Which statement best explains the two main types of heat transfer occurring?

• Convection causes the water to circulate, and Radiation transfers heat to the hands.

• Conduction causes the water to circulate, and Convection transfers heat to the hands.

• Radiation causes the water to circulate, and Conduction transfers heat to the hands.

• The dark color of the pot absorbs heat, which is then conducted through the air to the hands.

Factors Affecting Thermal Energy Transfer

• Different materials need different amounts of energy to change their temperature.

• More mass requires more thermal energy to change its temperature.

• The surrounding environment affects the rate of energy transfer.

Multiple Choice

Which of the following is a factor that affects how much thermal energy is needed to change an object's temperature?

• The mass of the object.

• The color of the object.

• The shape of the object.

• The magnetic field of the object.

Multiple Choice

A student has a 10-gram piece of clay and a 50-gram piece of the same clay. Which piece would require more thermal energy to warm up by 10 degrees, and why?

• The 50-gram piece, because it has more mass.

• The 10-gram piece, because it is smaller.

• They would both require the same amount, because they are the same material.

• It depends on the surrounding environment, not the mass.

Multiple Choice

You want to design an experiment to test which of two different materials, Material X or Material Y, heats up faster. To ensure your test is fair, what factors must you keep the same for both materials?

• The mass of the materials and the surrounding environment.

• The mass of the materials and their starting color.

• The surrounding environment and the shape of the materials.

• The starting temperature and the cost of the materials.

Thermal Properties and Design

• Conductors are materials that transfer heat well, like cooking pans.

• Insulators are materials that block heat, like a winter coat.

• Specific heat is the energy needed to raise a material's temperature.

• Conductors allow thermal energy to flow easily through them, such as metals like copper and aluminum.

• Insulators resist the flow of thermal energy, keeping heat in or out, like wood, rubber, or plastic.

• Specific Heat is the amount of thermal energy needed to raise the temperature of 1 kg of a substance by 1°C.

Multiple Choice

What is the primary function of an insulator?

• To block the transfer of heat.

• To transfer heat very quickly.

• To increase a material's temperature.

• To store thermal energy for later use.

Multiple Choice

If you need to make a pan for cooking food on a stove, which type of material would be most important to use for the main body of the pan?

• A material that is a good conductor.

• A material that is a good insulator.

• A material with very low specific heat.

• A material with very high specific heat.

Multiple Choice

A company is designing a new cooking pot that heats up very quickly but has a handle that stays cool. Based on these needs, which design choice is best?

• The handle should be an insulator, while the pot should be made of a material with low specific heat.

• The handle should be a conductor, while the pot should be made of a material with high specific heat.

• Both the handle and the pot should be made of a material with high specific heat.

• Both the handle and the pot should be made of a good insulator.

Kinetic Energy and Energy Transfer

• Energy is always conserved; it just moves between objects.

• Pushing a swing transfers energy, increasing its kinetic energy.

• A car's kinetic energy becomes thermal energy in the brakes when it stops.

Multiple Choice

Which statement best describes the principle of energy conservation?

• Energy is created by motion and disappears at rest.

• Energy is not created or destroyed, only transferred or transformed.

• Some types of energy can be lost forever.

• Energy is only found in objects that are hot.

Multiple Choice

What is the relationship between a person pushing a swing and the swing's kinetic energy?

• The swing produces new energy with each push.

• Energy is transferred from the person to the swing, increasing its motion.

• The swing's energy is lost to the air as it moves.

• Energy is converted from motion to heat in the swing's chains.

Multiple Choice

A car is traveling at high speed and then applies its brakes, causing them to become very hot. What is the best explanation for why the brakes get hot?

• The car's kinetic energy was destroyed by the force of the brakes.

• The brakes created new energy in the form of heat.

• The car's kinetic energy was converted into thermal energy in the brakes.

• The kinetic energy was sent back to the car's engine.

Thermal Expansion and Contraction

• Heating causes the particles in a substance to spread out and expand.

• Cooling causes the particles to move closer together and contract.

• Bridges have expansion joints to prevent buckling from thermal expansion.

Multiple Choice

What happens to the particles in a substance when it expands due to heating?

• They spread out and move farther apart.

• They get closer together and shrink.

• They change into a different type of particle.

• They stop moving completely.

Multiple Choice

What is the key difference between how heating and cooling affect the particles in a substance?

• Heating causes particles to spread out, while cooling causes them to move closer together.

• Heating makes a substance heavier, while cooling makes it lighter.

• Heating changes the color of a substance, while cooling does not.

• Heating only affects solids, while cooling only affects liquids.

Multiple Choice

Why would a long bridge built without expansion joints be at risk of damage on a very hot day?

• The heat causes the bridge materials to expand, which can lead to buckling.

• The sun's rays make the bridge materials weaker and more likely to break.

• The heat causes the bridge to contract, creating dangerous cracks.

• The hot air makes the cars driving on the bridge much heavier.

​

Common Misconceptions

Misconception	Correction
Heat and temperature are the same thing.	Temperature measures particle energy. Heat is the transfer of that energy.
When an object slows down, its energy is lost.	Energy is transferred to other forms, such as thermal energy.
A wool blanket creates its own heat.	A wool blanket is an insulator that slows the transfer of body heat.
All objects at the same temperature feel the same.	Conductors transfer heat faster than insulators, so they feel different.

​

Summary

• Heat is energy that transfers from a warmer object to a cooler one.

• Heat moves through conduction (touch), convection (fluids), and radiation (waves).

• Conductors transfer heat easily, while insulators slow heat transfer down.

• Most materials expand when heated and contract when they are cooled.

Poll

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

• 1

• 2

• 3

• 4