• Question: why do balloons fly with helium in them but not with our air when we blow them up?

    Asked by anon-1953 to Donna, Jo, Mark, timcraggs on 24 Jun 2010 in Categories: .
    • Photo: Donna MacCallum

      Donna MacCallum answered on 23 Jun 2010:

      Great question and all to do with the mass of helium relative to the components of air.
      Helium is lighter than air, therefore can float – other gases that can do this include hydrogen (which was used in airships until there was a massive explosion – see the Hindenburg)

    • Photo: Joanna Buckley

      Joanna Buckley answered on 23 Jun 2010:

      Gooood question, abcdefghijklmnopqrstuvwxyz.

      Helium is lighter than air. It’s got a lower density so it floats in air.

      Helium weighs 0.1785 grams per litre and Nitrogen weighs 1.2506 grams per litrre. Since nitrogen makes up about 80 percent of the air we breathe then that means helium is waaaaay lighter 🙂

    • Photo: Tim Craggs

      Tim Craggs answered on 24 Jun 2010:

      Alphabet – this is an excellent question (and one I definitely know the answer too!).

      When we blow up a balloon, we put the same air into the balloon (minus a bit of oxygen and plus a bit of carbon dioxide) as the air in which we want the balloon to fly. So there is no difference in density or mass between the air inside the balloon, and the air outside of the balloon.

      However, when we fill a balloon with helium, it will float, because helium is much less dense than air, so it weighs less for the same volume. Helium balloons follow the same principle as you do when you float in the water; the law of buoyancy. If the water you displace weighs more than you do, you will float. Same for the helium balloon.

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