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Thermal Energy is Total Kinetic Energy

by Ron Kurtus (revised 22 March 2007)

The thermal energy of an object consists of the total kinetic energy of all its atoms and molecules. It is a form of energy related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical motion, radiation and thermal conduction.

Questions you may have include:

• How can thermal energy be created?
• What are internal reactions?
• What are external effects?

This lesson will answer those questions. There is a mini-quiz near the end of the lesson.

Useful tools: Metric-English Conversion | Scientific Calculator.

Creation of thermal energy

Thermal energy is the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is sometimes confused with internal energy or thermodynamic energy. They consist of the sum of the internal kinetic energy (thermal energy) and the potential energy of an object. You may need to make sure which definition a teacher or book is using.

Kinetic Theory of Matter

The Kinetic Theory of Matter states that matter consists of atoms or molecules in random motion. Those moving particles can transfer their kinetic energy to other nearby particles. The total kinetic energy of all the particles in an object make up the thermal energy of that object.

Temperature and heat

Temperature and heat are related to thermal energy.

• Temperature is defined as the average kinetic energy of all the atoms or molecules in an object.
• Heat is defined as the flow of thermal energy from an object of one temperature to an object of another temperature. You feel the flow of heat when warm air from a furnace reaches you.

(See Temperature and Heat for more information on those subjects.)

Internal reactions

The thermal energy of an object can be created or increased by chemical and nuclear reactions, as well as electrical effects. Each releases or transfers energy that cause an object's internal particles to increase their motion and thus their kinetic energy.

Chemical

For example, some chemical reactions cause nearby molecules to accelerate, thus increasing the total thermal energy of the object. Burning is a common form of a heat-producing chemical reaction.

Nuclear

Nuclear reactions, such as nuclear fission or nuclear decay, give off high-speed particles that increase the thermal energy of a material.

Electrical resistance

The resistance to the motion of electrons in an electrical circuit cause the wire's molecules to increase their kinetic motion, thus increasing the thermal energy of the wire. Often you can feel the wire get warm when electricity is flowing through it.

External effects

External sources of energy such as mechanical motion, radiation and thermal conduction can also increase the thermal energy of an object.

Mechanical

Mechanical sources of heat are primarily external. When objects rub together, the friction causes molecules to increase their energy, resulting in heat. Likewise, bending or pounding on a piece of metal will cause it to get warmer.

Radiation

Light from the sun radiating on an object can transfer energy to the object's molecules, causing them to move faster. In other words, the object heats up. Radiation is considered a form of heat transfer.

Conduction of heat

The Kinetic Theory of Matter shows how the kinetic energy of a material's particles can be increased though collisions with faster nearby particles. This explains how a material can be heated through conduction heat transfer.

(See Heat Transfer for more information on that subject.)

Summary

Thermal energy consists of the total internal kinetic energy of an object due to the random motion of its atoms and molecules. It is related to heat and temperature. Thermal energy can be created internally with chemical, nuclear and electrical reactions. It can also be created or increased from external effects, such as mechanical, radiation and conduction effects.

Answers to Readers' Questions

Observe and learn

Resources

The following resources provide information on this subject:

Websites

Physical Science Resources

Books

Top-rated books on Thermal Energy

Miscellaneous

Mini-quiz to check your understanding

1. What is thermal energy?

2. How can nuclear decay increase the thermal energy of a material?

3. How does radiation increase thermal energy?

If you got all three correct, you are on your way to becoming a Champion in Physical Science. If you had problems, you had better look over the material again.

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Thermal Energy is Total Kinetic Energy