Upthrust during fluid friction is a net upward force exerted on an object submerged in a fluid (liquid or gas) or partly submerged in a fluid and partly in air. It is due to the pressure difference between the top and bottom surfaces of the object.

The upthrust is equal to the weight of the fluid displaced by the object. This principle is known as Archimedes' Principle.

$$Upthrust = \text {Weight of Liquid Displaced} $$

$$F_u=\rhoVg$$

where,

- \(F_u\) is the upthrust force

- \(\rho\) is the density of the fluid,

- \(V\) is the volume of the object,

- \(g\) is the acceleration due to gravity