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5.10: Thermal Energy

Difficulty Level: At Grade Created by: CK-12
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This unusual landscape is found in the hottest place in the U.S.: Death Valley, California. The temperature of the air near the ground can be as high as 57 °C (134 °F)—and that’s in the shade (if you can find any)! The temperature of the sand in the baking sun can be much higher. If you were to walk barefoot on the hot sand, it would burn your feet. The air and sand in Death Valley have a lot of thermal energy.

What Is Thermal Energy?

Why do the air and sand of Death Valley feel so hot? It’s because their particles are moving very rapidly. Anything that is moving has kinetic energy, and the faster it is moving, the more kinetic energy it has. The total kinetic energy of moving particles of matter is called thermal energy. It’s not just hot things such as the air and sand of Death Valley that have thermal energy. All matter has thermal energy, even matter that feels cold. That’s because the particles of all matter are in constant motion and have kinetic energy.

Thermal Energy, Temperature, and Mass

Thermal energy and temperature are closely related. Both reflect the kinetic energy of moving particles of matter. However, temperature is the average kinetic energy of particles of matter, whereas thermal energy is the total kinetic energy of particles of matter. Does this mean that matter with a lower temperature has less thermal energy than matter with a higher temperature? Not necessarily. Another factor also affects thermal energy. The other factor is mass.

Q: Look at the pot of soup and the tub of water in the Figure below. Which do you think has greater thermal energy?

A: The soup is boiling hot and has a temperature of 100 °C, whereas the water in the tub is just comfortably warm, with a temperature of about 38 °C. Although the water in the tub has a much lower temperature, it has greater thermal energy.

High temperature compared to high thermal energy

The particles of soup have greater average kinetic energy than the particles of water in the tub, explaining why the soup has a higher temperature. However, the mass of the water in the tub is much greater than the mass of the soup in the pot. This means that there are many more particles of water than soup. All those moving particles give the water in the tub greater total kinetic energy, even though their average kinetic energy is less. Therefore, the water in the tub has greater thermal energy than the soup. 

Q: Could a block of ice have more thermal energy than a pot of boiling water?

A: Yes, the block of ice could have more thermal energy if its mass was much greater than the mass of the boiling water.

Summary

  • The total kinetic energy of moving particles of matter is called thermal energy.
  • The thermal energy of matter depends on how fast its particles are moving on average, which is measured by temperature, and also on how many particles there are, which is measured by mass.

Review

  1. Compare and contrast thermal energy and temperature.
  2. Explain how an object with a higher temperature can have less thermal energy than an object with a lower temperature.

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    Vocabulary

    temperature

    Average kinetic energy of particles of matter.

    thermal energy

    Total kinetic energy of all the atoms that make up an object.

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    Difficulty Level:
    At Grade
    Grades:
    7 , 8
    Date Created:
    Nov 01, 2012
    Last Modified:
    Sep 13, 2016
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