Dow Education

The Incredible Shrinking Milk Jug Experiment

Procedure
Find a one-gallon, plastic milk jug. Go to the sink and run some hot water.*

Put a half-inch or so of hot water in the jug and then put on the cap. Now shake the jug so the water spreads around the inside of the jug. You should see the jug expand or get bigger.

Now, take the cap off and pour out the hot water. Next, run the same amount of cold water in the jug. Cap it again and shake. Watch the jug shrink!

Scientific Principle at Work
Chemistry provides insulating materials that help keep you comfortable at home or in the car, no matter what the weather. Insulating materials are manufactured by expanding gas inside plastic. Gases like air expand or contract with temperature. When the molecules (they’re the building blocks for everything) are heated, they move faster. When molecules are cooled, they move slower. A law in chemistry says for a given volume and number of molecules of vapor, the pressure follows the absolute temperature. You saw this law when the jug expanded and then shrunk.

*Note to teachers and parents: Be sure to supervise this experiment with younger children.