One of the first things a little scientist should learn is that heat causes things to expand (get bigger) and cold causes things to contract (get smaller). Things such as air will contract and take up less room when cooled. Similarly, things will expand when they get hot. If you don't believe this, carefully observe Dad's head the next time you break one of his expensive tools (Reeko tip - observe from a distance). Ok, so Reeko's gonna save you some heartache. Rather than test this by breaking one of Dad's tools, let's try the following experiment instead.

  1. Fill the bottle with hot water.
  2. Fill the bowl with cold water.
  3. Let both sit for one minute. Then empty out the bottle.
  4. Stretch a balloon over the mouth of the bottle.
  5. Set the bottle in the bowl of cold water.

Yes, Yes. Not quite as amazing as Dad's expanding head but still pretty cool.

The warm water heats the bottle. When the water is poured out the heated bottle then heats the air inside of it. When the bottle is placed in the cold water, the air inside the bottle cools and contracts (gets smaller and takes up less room), causing outside air to be drawn in, pulling the balloon in and inflating it inside the bottle.

Parent's Note. Expansion is an increase in the size of a body without the addition of material to the body. Most solids and liquids expand when they are heated and contract when they are cooled. Gases also expand when they are heated at a constant pressure. If a gas is heated in a container that prevents expansion, the pressure of the gas increases.

Heat causes expansion because it increases the vibrations of a material's atoms or molecules. In a gas, heat also increases the speed at which the atoms or molecules move about. The increased movement forces the atoms or molecules farther apart and the body becomes larger.