Question: Why do boats float?

Thomas Biggans answered on 15 Jun 2016:

Boats float because of a force called buoyancy.

A boat on water is being pulled down by gravity so the hull (the bottom part of the boat) pushes the water down out of the way. This pushes molecules in water below the boat closer together but these molecules don’t like being that close they want to go back to where they were so the water starts to push the boat back. This push from the water upwards is buoyancy and its strength is related to the amount of water pushed out of the way by the boat.

So to stop the boat sinking the strength of buoyancy has to be greater than or equal to the strength of gravity. The hull of the boat is designed with this in mind, the hull is built to be big enough that it pushes enough water out the way that the strength of buoyancy is equal to the strength of gravity. As the forces are equal the boat doesn’t go up or down it just floats.