How Does a Ship Float?
A ship floats because it is buoyed, or held up, by the water. When a ship is in the water, its big hull pushes some of the water aside. The volume of water displaced is equal to the weight of the ship. The buoyancy produced by this displacement holds the ship up.
It is not just something’s weight that makes it sink or float. It also depends on the object’s density-how tightly it is packed. A ship floats because it is designed with hollow spaces. A rock sinks because it has greater density and no air space. It weighs more than the water it displaces.
The science behind floating was first studied by an ancient Greek scientist named Archimedes. He figured out that when an object is placed in water, it pushes enough water out of the way to make room for itself. This is called displacement.
When an object enters water, two forces act upon it. There’s a downward force (gravity) that’s determined by the object’s weight. There’s also an upward force (buoyancy) that’s determined by the weight of the water displaced by the object.
An object will float if the gravitational (downward) force is less than the buoyancy (upward) force. So, in other words, an object will float if it weighs less than the amount of water it displaces.