Why do some objects, such as doors and windows, get bigger and smaller?

Updated February 21, 2017 | Factmonster Staff

Have you noticed that closet doors don’t close as easily in the summer as they do in the winter? It’s because they expand in the heat of the summer and contract during the cold winter. Everything on Earth is made up of tiny particles called molecules, which are in constant motion. When the molecules heat up, they move faster, pulling apart from one another. As they move apart, they take up more space, causing even solid objects to grow slightly larger. Molecules slow down as they cool, and they take up less room. This causes things to shrink a little bit. (Water is an exception. When it freezes, the molecules line up in such a way that the ice takes up more space.)

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