Why do ships float?

Sean and Robot have been thinking about the most basic boat bamboozler of all – why DO boats float? After all, they’re massive heavy things!

Well, ships partly float and partly sink – and this is all to do with its own weight and how much weight it carries (for example from passengers or cargo). The greater the total of these two weights, the lower a ship sits in the water.

In the third century BCE, a Greek mathematician called Archimedes noticed how the water level rose as he immersed his body.

As a ship displaces – or in everyday language – pushes the water out the way, the displaced water wants to return to its original location – but as that’s where the ship is now, the water pushes the ship upwards. The force which pushes the ship up is called the buoyancy force.

One of the most basic rules is that an object will sink if it weighs more than the same volume of water. A ring might be small but it’s more dense than the same sized space of water. A ship might be massive but so is the amount of water it displaces.

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