• Question: Why do boats float?

    Asked by dalvindk to Damien, Rachael, Simon, Suzi, Tim on 16 Jun 2011.
    • Photo: Suzi Gage

      Suzi Gage answered on 14 Jun 2011:

      Hi @dalvindk
      Good question! I didn’t know the answer so I’ve done some reading to try and find out!
      When you put something in water, if it sinks, water is displaced (moved) to make room for it. This is why, if you fill your bath completely full and then get in it, the water will spill over the side. If the thing you put in water weighs less than the amount of water it needs to displace, then it will float, because there is a buoyancy effect of water. That is, if something is in water, the water pushes on it from all sides, and the net direction of this force is upwards.

      So if you’re designing a boat, you can use heavy material, as long as you make the boat sooooo big that it will displace more water than it’s weight.

      Hope this answers your question 🙂

    • Photo: Damien Hall

      Damien Hall answered on 16 Jun 2011:

      I’m not a physicist, but I think it has to do with the density of the material. A stone, even a very small one, usually sinks because it is very dense (there isn’t much space for air within it). A piece of wood might sink if it is very dense, but most wood floats because it is not very dense. If you think about a boat, it can be very heavy, but it also contains a lot of air (in the rooms within the boat) – so, overall, it is not very dense, and it floats.

      I think!

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