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Thermal (or heat) energy can be either taken in or given off from substances. The amount of energy that is added or taken away changes the molecular motion that is observed. As you learned last year in 7th Integrated Sci-ber Text, the molecule motion determines which phase of matter is observed. Slow moving molecules are found in solids while rapid moving molecules are present in gases. Liquids have molecules in motion that are slower than gases, but much more rapid than a solid.

Increasing the motion of the molecules can get the substance to change phase. If you slow down the molecules in a gas, the substance will change to a liquid. In a similar manner, if you increase the molecule motion of a solid, it will change to a liquid.

Remember that water is found in all three phases here on the Earth.



As you look at the photographs above, answer the following questions:

  1. How would you describe the thermal energy of the molecules in the solid form of water shown above?
  1. Which of the phases of matter above has the greatest molecule motion?
  1. How would you describe the amount of thermal energy of the molecules in the gas form of water shown above?
  1. Which phase of matter above has molecules closest to each other?
Check your answers by highlighting the box below.
1. Very low energy, 2. Gas, 3. High energy, 4. Solid

Remember that an increase in the amount of thermal energy will increase the motion of the molecules in the substance. The greater the increase of thermal energy, the greater the motion of the molecules. The amount of thermal energy will determine if the material is a solid, liquid, or gas.

Temperature refers to how hot or cold something is, it is defined as the average value of the kinetic energy of the molecules of a substance. That is why the temperature of a substance is always changing. Heat is flowing into and out of matter all the time.

Review Science safetey rules here.

Get the plug-ins: Get Adobe Acrobat Reader , and Get Quicktime Player. (The QuickTime plug-in is needed to play sounds and movies correctly.)

Want to share photos of you or your friends doing this activity? Send it in an e-mail with the following information:

  1. The title of the activity
  2. The URL (Internet address)
  3. Your name.

Remember that no pictures can be used that show student faces or student names on it. 

Teachers should view the Teacher Site Map to relate Sci-ber text and the USOE 8th grade science core.

Updated October 24, 2008 by: Glen Westbroek

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