Thermal expansion happens when an increase in temperature makes particles (molecules) in a substance move faster, which expands the substance.

Materials You Will Need

• one plastic straw
• boiling water
• a flat piece of Styrofoam

What to Do

1. Poke a hole in the piece of Styrofoam with the plastic straw.
2. Put the piece of Styrofoam off to the side and place half of your straw into boiling water for 20 seconds.
3. Now try to put the straw back through the hole you made in the Styrofoam. It doesn’t fit through anymore! Why? The heat of the boiling water caused the molecules of plastic inside the straw to move faster, thus making the straw expand (get bigger)! It’s called thermal expansion!