• Question: How do we know that water particles move around when they are heated?

    Asked by petrosthegreekgod to Betul, Bridget, Ceri-Wyn, Maria on 25 Jun 2010 in Categories: .
    • Photo: Ceri-Wyn Thomas

      Ceri-Wyn Thomas answered on 24 Jun 2010:

      All molecules in all materials vibrate all the time. Even in ‘solid’ materials. Only
      by cooling things down
      to absolute zero, -273 centigrade, can we stop all particle motion. This is the
      coldest temperature you
      can get. Water particles must be able to move a lot,
      which is why water flows. As you heat things up, they are able to move and vibrate
      more and more. It is this
      vibration that our bodies ‘feel’ as heat. Really the question is the other way
      around, why do we feel
      water particles moving around and vibrating faster as heat? As the water is heated
      more and more, and the
      particles move faster and faster, eventually they move fast enough to escape from
      the water and become a gas,
      steam or water vapour. This happens when water boils, at 100 degrees C.

    • Photo: Bridget Waller

      Bridget Waller answered on 25 Jun 2010:

      Well, we know that all particles move when they have energy (when they are hot), and move less when they don’t (when they are cold). Heat and energy are basically the same thing in this sense. We can demonstrate this through experiments, such as brownian motion experiments, have you done that at school? Here particles suspended in air or fluid bounce about randomly, because they are being hit by all the smaller particles that we can’t see (the water, or air that they are floating in). So this means that all particles are moving in some way, and are not still. Even ther particles in ice have some energy (albeit a small amount), and are moving very, very slowly. So when water particles are heated, they gain energy and move more. When they gain a certain amount of energy they turn into vapour and escape the liquid – which is what is happening when the water boils. I would clarify all this with your teacher if i were you…been a while since I did this stuff. 🙂

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