CogKnoSys

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Physical

Thermal Energy

Thermal energy is the energy tied to the random motion of particles in matter, a term often used for internal energy or heat.

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The idea

Thermal energy is the energy that matter has because its particles are always moving. The atoms and molecules in everything jiggle, spin and vibrate. When they move faster, the temperature goes up. The total amount of thermal energy also depends on how much matter there is. A bathtub of warm water holds more of it than a cup of hot tea, because the bathtub has far more moving particles.

Scientists use the term "thermal energy" in more than one way, which can cause confusion. Sometimes it means internal energy, the energy contained within a body of matter. Sometimes it means heat, which is energy moving between a body and its surroundings in ways other than work or the transfer of matter. So when you read the term, check whether the writer means energy stored inside an object or energy flowing into or out of it.

Heat can move in several ways. It travels by conduction when moving particles bump into their neighbors, as when a metal spoon warms up in hot soup. It also travels as electromagnetic radiation, like the warmth you feel from sunlight. In liquids and gases, flowing currents can carry it, which is called convection. Heat can also be produced by friction, as when you rub your hands together, and by electric current passing through a wire. Scientists measure heat in joules (J), the standard unit of energy.

Check yourself

Question 1 of 2

What is it called when flowing currents in a liquid or gas carry heat from place to place?

Pick one. The first pick counts.

Composition

what it's made of

  • Particle motion — The random jiggling, spinning and vibrating of atoms and molecules.
  • Internal energy — The energy contained within a body of matter.
  • Heat — Energy moving between a body and its surroundings, other than as work or with moving matter.
  • Temperature — A measure that rises as particles move faster.
  • Joule — The SI unit used to measure heat and other energy.

Connection

how it relates

Under Energy Forms

Related

  1. Frictionstrength 80 of 100

    Friction turns the energy of motion into heat, which is why rubbing surfaces warm up.

  2. Metals and Alloysstrength 40 of 100

    Metals conduct heat well, which is why cooking pots are usually made of metal.

Cause and effect

  1. Evaporationstrength 70 of 100

    Adding heat makes water molecules move fast enough to escape into the air as vapor.

Change

how and why it evolves

Past
Rudolf Clausius, one of the founders of thermodynamics, first set out internal energy in the first law of thermodynamics. In 1970 the physicist Mark Zemansky argued that the term thermal energy is best avoided, and he suggested the more precise terms internal energy and heat instead.
Now
Today the term still appears in some textbooks, alongside the more precise terms internal energy and heat.
Next
Devices such as heat pumps will likely grow more important as people try to waste less power.

Knowledge you can walk. Read the idea, then step up, across or down.

Thermal Energy

Thermal energy is the energy tied to the random motion of particles in matter, a term often used for internal energy or heat.

Learn, discuss, create, buy or invest

The idea

Thermal energy is the energy that matter has because its particles are always moving. The atoms and molecules in everything jiggle, spin and vibrate. When they move faster, the temperature goes up. The total amount of thermal energy also depends on how much matter there is. A bathtub of warm water holds more of it than a cup of hot tea, because the bathtub has far more moving particles.

Scientists use the term "thermal energy" in more than one way, which can cause confusion. Sometimes it means internal energy, the energy contained within a body of matter. Sometimes it means heat, which is energy moving between a body and its surroundings in ways other than work or the transfer of matter. So when you read the term, check whether the writer means energy stored inside an object or energy flowing into or out of it.

Heat can move in several ways. It travels by conduction when moving particles bump into their neighbors, as when a metal spoon warms up in hot soup. It also travels as electromagnetic radiation, like the warmth you feel from sunlight. In liquids and gases, flowing currents can carry it, which is called convection. Heat can also be produced by friction, as when you rub your hands together, and by electric current passing through a wire. Scientists measure heat in joules (J), the standard unit of energy.

Check yourself

2 quick questions, instant feedback.