• Question: What is fire? :)

    Asked by astroaaron to Ben, Jony, Katharine, Mark, Peter on 14 Nov 2011. This question was also asked by jaz7866.
    • Photo: Mark Basham

      Mark Basham answered on 14 Nov 2011:

      Hi astroaaron

      Not too sure what you mean, but I guess your asking what a flame is? So when something is burning it releases hot gas, and its those hot gases that you can see. Its a bit like how the neon gas in a neon lamp glows and you can see it.

      Hope that helps, and keep the great questions coming 🙂

    • Photo: Ben Still

      Ben Still answered on 14 Nov 2011:

      If you mean fire in the normal sense then it is energy released in heat and light form from the oxidisation of some chemical. Burning wood or charcoal turns Carbon into carbon monoxide and dioxide and releases heat and light energy in the chemical process. You can burn other things in the same way to release different amounts of heat and light. Hydrogen is used in rockets for example, when burnt (oxidised) is forms water H2O and a lot of heat and light energy.

    • Photo: Katharine Schofield

      Katharine Schofield answered on 14 Nov 2011:

      Fire is chemical process that needs three things – fuel (that is, something to burn), oxygen, and heat. Once there is enough heat to make the fuel/oxygen combination ignite, the fire will continue until one of those three things runs out (so either the fuel runs out, or the fire is starved of oxygen e.g. by throwing a blanket over it, or the heat source is taken away faster then the fire can produce it e.g. by throwing water on it).

      The chemical reaction releases energy in the form of heat and light and this is what you feel and see in the flames. Flames are a mixture of hot gases and solid particles (eg soot) released from the fire. Flames are different colours depending on the types of gases and solids being given off.

    • Photo: Peter Williams

      Peter Williams answered on 14 Nov 2011:

      There are two effects that contribute to a flame. The first is light that is given off by hot objects. If you throw a piece of metal in a furnace it will start to glow, this is the same, only in a flame these objects are suspended particles of soot. There is a technical name for this – “black body radiation”. Everything gives off black body radiation. It’s just that if it is cool, then that radiation is not in the visible part of the spectrum. Black body radiation is the main evidence we have for the Big Bang, but that’s another matter.
      The other component in a flame is called line emission. When the electrons around an atom “drop” from one energy (a large orbit if you imagine the atom as a planetary system) to a lower energy (smaller orbit) they emit a photon of a very well defined colour. The atoms taking part in the chemical reaction do this. You can see this effect in a street lamp. They are filled with sodium vapour. When an electric current excites them, the electrons jump up into a high orbit, then they drop down again. When they do this they emit a photon that is yellowy-orange. So street lights are that colour. If you do this with copper, it makes green. Potassium makes red, i think.

      Ask your teacher if the school has a spectrometer, using one of these you can see the lines in the line emission.

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