Experiment: Thermal Expansion

by STEM Scouts

By Brooke Myers, Capitol Area Council

Supplies Needed:

  • 2 Bowls
  • Boiling water
  • Ice Water
  • Recycled bottle
  • Balloon
  • Parent/Adult Supervision

Thermal Expansion is a quick and easy introductory lesson for students to begin exploring effects of temperature on matter. This experiment is very simple however can be used to frame particle behaviors. After this experiment, students should understand the direct relationship between temperature and volume of an object. Advanced students should understand the effects of temperature on particle behaviors and conservation of matter. Every time I show this demonstration at a community event or school, students believe that the air itself is rising due to the heat thus filling the balloon. Hot fluid will rise due to its change in buoyancy as a direct result of thermal expansion. Unpack this common phrase and help students connect the process. This clear distinction will help them to later understand Convection (experiment coming soon).

Common Preconceptions:

  • More air has gotten into the balloon
  • There is no hole in the bottle or balloon; therefore no way for air to escape or come in from the system once sealed.
  • Hot air rises
  • Technically, hot air rises. But more importantly, it takes up less space, is less dense, and will float higher due to this change of density. Hot air does rise, but that is not what causes the balloon to fill in the experiment

Parent Guide:
All matter is made up of small atoms. These atoms can be broken down into smaller parts, but if you’re teaching this to elementary school age, you can keep it simple with the word “particles.” Anytime anything is heated, its volume increases because of the interactions between particles. We observed the balloon increase in volume as the air in the bottle was heated. Thermal Expansion; when an object is heated, and its volume increases due to interactions between particles. (See solids undergo Thermal Expansion)

Download the Lesson Resource Guide

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