• Question: Why do some objects, such as doors and windows, get bigger and smaller in the winter and in the summer?

    Asked by PlumCurry to Ellen, Elliot, Hazel, Rupesh, Thomas on 15 Jun 2016.
    • Photo: Ellen Gill

      Ellen Gill answered on 15 Jun 2016:

      This is an interesting one!
      Heat is a form of energy, so when you heat a material you are actually giving the molecules in it more energy, which makes them react against each other more strongly. The effect is that the material pushes itself apart very very slightly. This is particularly obvious with metal frames. However, when a wooden window or doorframe gets bigger, chances are it’s damp and has swelled up with moisture.

    • Photo: Hazel Garvie-Cook

      Hazel Garvie-Cook answered on 15 Jun 2016:

      When objects heat up, the molecules inside the object move more so the object expands. So when it’s hotter in the summer, objects are likely to be a bit bigger.
      If the doors or the windows are made of wood, the explanation is a bit more complicated. Wood is made up of lots of small fibres. When a bit of moisture gets into the wood, some of those fibres move more than others, so the wood curves and warps out of shape. After a door has warped, it’s changed shape and won’t fit into its frame as easily as before.

    • Photo: Thomas Biggans

      Thomas Biggans answered on 16 Jun 2016:

      It’s all to do with temperature! When you heat something up you’re giving that object energy. In a solid object like windows and doors this energy makes the atoms that make the objects up vibrate so they start to push off each other. This means the object as a whole gets bigger.

      When the object cools down its losing energy so the molecules vibrate very little so they don’t really push off each other at all so the whole object gets smaller. This is an important thing to consider when building train tracks because you need to leave a gap between rails so they can expand and not break.

    • Photo: Elliot Jokl

      Elliot Jokl answered on 16 Jun 2016:

      The others have explained the physics very well. I’m just adding to say remember a nice and simple physics experiment that our teacher used to show this. He had a metal hoop and a ball that couldn’t quite fit through the hoop when the hoop was cold. If you then heat up the metal hoop with a bunsen burner, the hoop expands and the ball fits through.

      I managed to find a youtube video of this, which is annoyingly the other way around! Maybe I misremembered – it was a long time ago now! In this one, the ball fits through at room temperature, but if you heat the ball it expands and won’t fit through:

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