Why do boats float

What makes a massive ship, or for that matter, a rather small but stern boat glide effortlessly on water? Mass is supposed to sink in water, then what makes these considerably heavy masses float on water? The truth is that our prior knowledge of mass and its sinking behavior in fluids is half cooked, and half knowledge, as we all know, is a dangerous thing. Actually, a solid mass can float on water, provided that it displaces an amount of water equivalent to its own weight. The first impulse on placing a solid in water is the weight of the solid acting on the water surface, and pushing the layer down, thus sinking. Generally, the sudden force is quite large and the sinking is instant.

This is because the average density of the solid is a lot more than that of water. Obviously, this is expected, considering that core matter makes up solids. The molecules of matter, when packed tightly together, result in a high average density. However, this is precisely where the situation takes an interesting turn. Ships and boats, though superficially very bulky, are actually designed in such a manner that the insides host a lot of air, rather than matter. The complete package, though undoubtedly spacious, is not as bulky as it appears to be. The comparatively restrained average density of the boats makes sure that the boat has enough time to displace a sufficient amount of water before it can sink, thus avoiding the sinking and floating on the water. This is the gist of the Archimedes principle. The displaced fluid exerts an upward force on the object that causes the displacement. Without any upward balancing force, sinking of the object is inevitable. Plus, there are two conditions that this upward force, or the buoyant force, must satisfy to be of any use.

First, it must be equivalent in impact to the weight of the body it attempts to save from sinking. Secondly, it must act before the body has sunk! Boats and ships are designed keeping these things in mind. They displace enough water, swiftly enough, in order to sustain themselves on the water surface. Upward force, due to the rapid displacement of water, keeps pushing the boat upwards and this balances the downward thrust applied by the boat on the water. The net transaction results into the safe sailing of the boat. In fact, this explanation holds true for most of the objects that are able to float over water.