Science Concepts—Expand and Contract

Summary: As the ocean’s temperature increases, its volume expands. In this activity, students heat and measure volume of air in a balloon to demonstrate the concept that heat causes most substances to expand and become less dense. Then they observe a demonstration that shows that liquid water (above 4 degrees C) also expands when heated.

Concepts to teach:


  1. When most materials are heated (including water above 4 degrees C ) the volume increases due to a process called thermal expansion.
  2. Thermal expansion is the primary cause of climate induced sea level rise.
  3. A model can demonstrate a scientific concept.

Standards: NGSS Performance Expectations

  • 4-PS3-2.Make observations to provide evidence that energy can be transferred from place to place by sound, light, heat, and electric currents.
  • 5-PS1-1. Develop a model to describe that matter is made of particles too small to be seen.

Specific Objectives:
Students will be able to:

  1. Understand that heat causes most substances to expand and become less dense
  2. Set up a simple data table to record results
  3. Observe that heated water has more volume than cooler water
  4. Explain how sea level rise results in part from thermal expansion

Activity Links and Resources:

  • Activity: Size-changing Science: How gases expand and contract from Science Buddies at Scientific American
    • Students measure the volume of air in a balloon before and after the air has been cooled or heated, and relate the results to the kinetic energy of molecules.
    • Check for potential misconceptions: Ask students to draw a picture of what is going on inside the balloon. That is, a closed balloon has the same number of molecules inside it although the temperature and volume of the balloon changes. Example
  • Demonstration: COSEE’s Thermal Expansion and Sea Level Rise – This experiment demonstrates the relationship between water volume and water temperature.
    • Set up this experiment as a demonstration to illustrate that water also expands when heated. Train a flex camera on the ruler and project the image on the screen for the entire class to follow and collect data.
  • Discuss with students what effect an increase in ocean temperature will have on its volume. If ocean volume increases, where will the ‘extra’ water go?


  • In the experiments, what happened to the balloon volume as the temperature changed?
  • Have students draw pictures of the balloons in the experiments to demonstrate their understanding of density and volume.
  • In the demonstration with liquid water, what happened to the water level when it was heated?
  • What happens to the volume of the Earth’s ocean when the temperature of the water increases? How does this affect sea level?