• Question: what is heavier hot air or cold air

    Asked by grafitipig to Alex, Alison, Gavin, Helen, Miranda on 9 Jul 2012.
    • Photo: Alex Ireland

      Alex Ireland answered on 9 Jul 2012:

      Hot air is lighter, because when it gets heated up it expands and so its density is less. This is why hot air balloons can fly because they’re filled with hot air which is lighter than the cold air outside.

    • Photo: Miranda Armstrong

      Miranda Armstrong answered on 9 Jul 2012:

      Hi grafitipig. In hot countries this is part of the reason that there are thunder storms later in the day during summer. In these countries because the ground temperature is hot during the day the air heats up and rises. Warm air has a greater ability to hold water vapor and this process can cause thunder clouds to form. I grew up in South Africa where it gets pretty warm during the summer and we would often get thunder storms in the afternoons on hot summer days because of this.

    • Photo: Alison Atkin

      Alison Atkin answered on 9 Jul 2012:

      Cold air is definitley heavier. Cold air will sink below hot air, which is sometimes why in the winter, the downstairs of a house might feel cold, while the upstairs is nice and warm!