• Question: Why do boats float?

    Asked by Little M to Ahmed, Francesca, George, James, Nitheen on 17 Nov 2014.
    • Photo: Ahmed Osman

      Ahmed Osman answered on 17 Nov 2014:

      THANKS FOR THIS GENIUS QUESTION
      The key factor is the density of the material if it is denser it will sink. An object will float if it weighs less than the amount of water it displaces. This explains why a rock will sink while a huge boat will float. The rock is heavy, but it displaces only a little water. It sinks because its weight is greater than the weight of the small amount of water it displaces.
      Hope it is clear now
      Thanks
      Ahmed

    • Photo: Francesca Paradisi

      Francesca Paradisi answered on 17 Nov 2014:

      Boats can be very different. If it’s a small wooden boat than Ahmed’s answer explains it well, wood floats on water and can sustain a certain amount ow weight depending on the size of the boat. But I think more interesting is to explain how metal big ships float! They generally have airtight compartment which are filled with air so that they act as giant floaters and keep the boat up. Also remember Archimede’s principles that says that an “upward buoyant force that is exerted on a body immersed in a fluid, whether fully or partially submerged, is equal to the weight of the fluid that the body displaces”, in short the water will push the boat up towards the surface, and the bigger the boat the stronger the upward push.

    • Photo: James Sullivan

      James Sullivan answered on 17 Nov 2014:

      ^^ Francesca nailed it here.

    • Photo: George Dowson

      George Dowson answered on 17 Nov 2014:

      Francesca is spot on, it’s all about balancing forces. If you’ve tried to push a football under water you’ll know how strong buoyancy forces are upwards. The downward force from the weight of the vessel must balance with the upward buoyancy. Overall the vessel must be less dense (in total volume) than the liquid it sits in. If the material is denser than water it needs a large air pocket to keep afloat to “spread the weight” across a larger volume.
      Like that it’s possible to build a metal or even concrete boat!

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