• Question: How do we swim in water? Why can we float? Is it because we are in a bubble, or we have air in our bodies that helps us to float? And why can we breathe underwater, do we have secret gills that enable us to have a fish like swim pattern and breathing pattern in water?

    Asked by to Roy, Rowena on 20 Mar 2014. This question was also asked by .
    • Photo: Rowena Fletcher-Wood

      Rowena Fletcher-Wood answered on 20 Mar 2014:


      The fat in our body causes us to float because fat is less dense than water. The muscles and bones are heavier and make us sink, so the degree to which you can float depends upon the fat/muscle ratio. This doesn’t mean you have to be overweight: if you are smaller but don’t exercise very much you still have a lot of fat. There is some air in our bodies, but the fat dominates. When a person dies the body swells up as cells begin to break down and this makes them lighter and so they float.

      We used to be fish, so we used to have gills, but sadly they are no longer there. We can breathe out underwater, but not in. I have tried breathing in under water and it was a very unpleasant experience. If you try holding your breath underwater you can do so for longer and longer times, but there will always be a limit and it isn’t exactly a safe game to play. Better leave it up to the fishes.

    • Photo: Roy Adkin

      Roy Adkin answered on 20 Mar 2014:


      Good question Olivia!
      We are essentially made up of 78% water as it is so water floats about in water so that’s one thing…we’re almost the same density. Next time you’re in the bath or swimming pool and lay on your back and breath all the air out, then breath in hard (make sure your head is above the water!!). You’ll notice you will rise and fall quite markedly. A lung full of air will increase you buoyancy (ability to float) a lot.
      As for the swimming bit…water molecules are held together by quite a strong intermolecular force called hydrogen bonding…it’s rather hard to wade or swim because you have to break trillions and trillions of those bonds for every push forward.
      I hope that answers your question 🙂

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