Heat pushes the parts or atoms of an object farther from each other, and thus its size is increased.
What does a blacksmith do with a tire before putting it on a wheel?
He heats the tire red-hot.
Why does he heat the tire red-hot?
So that it will be increased in size, and will go on the wheel more easily.
What takes place as the tire cools?
It becomes smaller, and thus binds the parts of the wheel tightly together.
When a fire is made in a room, why does the furniture often make a snapping noise?
Because heat expands the wood, and the particles make a snapping noise upon separating.
Why does a stove make a crackling noise as it grows hot?