Buoyancy is the tendency of an object to float in a fluid. All liquids and gases in the presence of gravity exert an upward force known as the buoyant force on any object immersed in them. Buoyancy results from the differences in pressure acting on opposite sides of an object immersed in a static fluid. After reading this article, you will be able to explain the buoyant force and why fluids exert an upward buoyant force on submerged objects.


The buoyant force is the upward force exerted on an object wholly or partly immersed in a fluid. This upward force is also called Up thrust. Due to the buoyant force, a body submerged partially or fully in a fluid appears to lose its weight, i.e. appears to be lighter.

The following factors affect buoyant force:

  • the density of the fluid
  • the volume of the fluid displaced
  • the local acceleration due to gravity


Causes of Buoyant Force


When an object is immersed in water or any other fluid, we observe that the object experiences a force from the downward direction opposite to the gravitational pull, which is responsible for the decrease in its weight. This upward force exerted by the fluid opposes the weight of an object immersed in a fluid. As we know, the pressure in a fluid column increases with depth. Thus, the pressure at the bottom of an object submerged in the fluid is greater than that at the top. The difference in this pressure results in a net upward force on the object, which we define as buoyancy.

Applications of Buoyancy

Buoyancy (upthrust) makes it possible for swimmers, fishes, ships, and icebergs to stay afloat. Some applications of buoyancy are given in the points below.

Hot Air Balloon

The atmosphere is filled with air that exerts buoyant force on any object. A hot air balloon rises and floats due to the buoyant force. It descends when the balloon’s weight is higher than the buoyant force. It becomes stationary when the weight equals the buoyant force.


A ship floats on the surface of the sea because the volume of water displaced by the ship is enough to have a weight equal to the weight of the ship. A ship is constructed in a way so that the shape is hollow to make the overall density of the ship lesser than the seawater. Therefore, the buoyant force acting on the ship is large enough to support its weight.


A certain group of fishes uses Archimedes’ principle to go up and down the water. To go up to the surface, the fish will fill its swim bladder (air sacs) with gases (clever, isn’t it?). The gases diffuse from their own body to the bladder and thus make the body lighter. This enables the fish to go up.