The law of floatation

The Law of Floatation

The law of floatation states that a floating object displaces its own weight in the fluid in which it floats. This means that when an object is floating on a fluid (like water), the weight of the fluid displaced by the object is equal to the weight of the object itself. The upthrust force, which is the force that keeps an object afloat, is equal to the weight of the displaced fluid.

Key points of the law of floatation

1. The upthrust force on a floating object depends on the volume of the object that is submerged in the fluid.
2. For an object to float, the upthrust force must be equal to the gravitational force (the weight of the object).
3. If the upthrust force is greater than the weight, the object floats. If the weight is greater than the upthrust force, the object sinks.

Example: Wooden block in water

If a wooden block is floating in water, the volume of water displaced by the submerged part of the block is equal to the weight of the block. The upthrust force acting on the block is equal to the weight of the displaced water, which supports the block and keeps it afloat.

Relationship between the weight of the wooden block and the weight of displaced water

The weight of the wooden block is equal to the weight of the displaced water. This is the key principle of the law of floatation.

A floating block of wood

Application of the law of floatation in water transport

1. Ships: Ships are large and heavy, but they do not sink because the amount of water displaced by the ship is equal to its weight. The ship's design ensures that it displaces enough water to balance its weight, allowing it to float. The ship is partially submerged, and the volume of water displaced by the submerged part of the ship is exactly equal to the ship's weight.

A floating ship

2. Submarines: Submarines use the law of floatation to both float and sink in the water. A submarine has special tanks that can be filled with water or air:

   • When the tanks are filled with water, the submarine's density becomes greater than that of water, and it sinks.
   • When the water is replaced with air in the tanks, the submarine's density becomes less than that of water, and it floats again.

3. Research Ships: Research ships that explore deep water can adjust their buoyancy to move horizontally or vertically. This is achieved by adjusting the amount of water in their tanks, enabling them to float or sink as needed for their research missions.