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Science for Kids: Learn About Expansion and Contraction

Updated on April 17, 2017

Words You Need to Know

Expand means to become larger

Contract means to become smaller

Expansion and Contraction

Have you ever heard your house creaking? It can sound frightening but it's nothing to worry about. Materials, like the wood used to build your house, expand and contract.

When the temperature of a material heats up, it expands. Expands means it gets a little bigger. This happens because the particles move faster and spread out. So, the material gets slightly bigger. When a material cools down the opposite happens. It gets slightly smaller. Getting smaller is called contraction.

The particles themselves don't get any bigger or smaller. It's the amount of space between them that changes.

The mercury in thermometers rises or falls because the liquid inside expands and contracts based on the temperature.

Particles spread out when heated up
Particles spread out when heated up | Source

Expansion and Contraction Experiment

This is a simple experiment you can try to see expansion and contraction for yourself. Get a parent to help you.

You will need:

  • A plastic bottle with a lid
  • A container of hot tap water
  • A container of ice cold water

Take the lid off the bottle. Hold the bottle in hot water for a couple of minutes. While the bottle is still in the water screw the lid on tight. Now hold the bottle in the cold water for a few minutes. What happens to the bottle?

Expansion Joints

Engineers who design buildings, roads, sidewalks, bridges and railway lines have to consider expansion and contraction. If they don't, the structures they design will break when they expand and contract with temperature changes. Expansion joints are designed to prevent this.

Expansion Joint On a Bridge



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      a person 2 weeks ago

      i already no this stuff im sorry but its a good vid for people who dont

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      tomzy 3 years ago

      wow. what i have been looking for is here. so reliable