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Buoyancy - Definition, Application and Center of Buoyancy

Most of us might have noticed that our body feels much lighter in weight when we go swimming or take a lift. Even while drawing water from a well with the help of a bucket, we should have noticed the same thing that the bucket feels light until it is immersed in water, but could feel its whole weight when it is outside and filled with water in it.

From this, we can learn that when a body or an object is immersed in fluids such as water, it experiences a force that originally formed from the ground and acts upwards. This force can act opposite to gravitational pull. This force is responsible for the decrease in weight. Hence, this can act as a reason lighter-weight objects such as paper boats, balls, float instead of sinking. The objects that sink contain relatively heavier weights such as anchors for steel rods. In this article, we will widely discuss the buoyancy concept and other topics related to buoyant force in a detailed manner.

Definition of buoyancy

Buoyancy is a common term that is used to describe a force that causes objects to float on liquid substances instead of sinking. Buoyancy can be exerted on a body that is partially or wholesomely immersed inside a fluid. This force is a cause that happened because of the pressure difference, which acts opposite to that of the object immersed inside a static fluid. This force is called buoyant force and buoyancy is a phenomenon due to this force.

Hence, buoyancy can be defined as the upward force given by the static fluid on the body when it is submerged in the fluid. Buoyant force’s unit is Newton (N). When an object is submerged in water, it can displace some amount of water because of its weight. The more the weight of the body, the more the amount of water gets displaced. The volume of football and tennis balls might be similar but their density and size differ a lot. Also, a steel bar can easily sink inside water whereas a huge boat or ship cannot. Hence, the quantity of the displaced water is seen going in the upward direction with respect to buoyant force.

Center of buoyancy

Center of buoyancy is nothing but the point where the force of buoyancy can be applied. The force of buoyancy seems to be vertical, while we term the center of buoyancy as the point where the center of gravity is present which was displaced by the submerged body.

Density and relative density

We should know the concepts of density and relative density first before learning the concepts of buoyancy.

Density: Density can be obtained by dividing mass of the object by its volume. This can tell how tightly a matter is packed. The formula for density is given below,


SI unit of density can be measured in terms of kg/m3 (kilogram per cubic meter). Density can be numbered as 0.9584g/cm3 at a temperature of 100° C. Relative Density:

 Relative density: Relative Density is described as the ratio of density of the substance to the density of water at a temperature of 4 C. This can also be called the specific gravity of the substance.


As we can consider relative density as the ratio of similar quantities, it contains no unit.


As seen above, the buoyant force is nothing but the upward force produced on a body that is fully or partly immersed inside a fluid. This upward force is termed upthrust. When this force occurs, the object or body will feel lighter.

A body that has a higher density compared to the fluid while immersed in liquid undergoes sinking. Meanwhile, if a body whose density is lighter and lesser than that of the fluid or if it is shaped appropriately such as boats and ships, tends to float on the surface. To sink into the water, the relative density of the object needs to be greater than 1 whereas if the relative density of an object or body is less than 1, then it will float on the liquid surface. The buoyant force highly depends on the following components,

  • Volume present in the object which is submerged in water should be equivalent to the volume of the displaced fluid.
  • The density of the fluid in which the object or body is put.

Application of Buoyancy

The following are some places of applications of buoyancy:

  • Hot-air balloon
  • Ship
  • Boat
  • Fish
  • Submarine
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