Civil Engineering Questions
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Ali Hamza
Mechanical
25 Jan 2019

What is Buoyancy??

Buoyancy:

When a body is immersed in a fluid, an upward force is exerted by the fluid on thebody. This upward force is equal to the weight of the fluid displaced by the body andis called the force of buoyancy or simply buoyancy.

Centre of buoyancy:

It is defined as the point, through which the force of buoyancy is supposed to act. Asthe force of buoyancy is a vertical force and is equal to the weight of fluid displacedby the body, the centre of buoyancy will be the centre of gravity of the fluiddisplaced.This result is known as Archimedes’ principle.

If W>R , object will sink

If W

If W=R, object is neutrally buoyant, i.e. it will remain in place without either sinking or rising.

A BODY IMMERSED IN TWO FLUIDS

If a body is immersed so that part of its volume V1 is immersed in a fluid of density ρ1 and the rest of its volume V2 in another immiscible fluid of mass density ρ2 Upthrust on upper part, R1 = ρ1gV1 acting through G1 , the centroid of V1 , Upthrust on lower part, R2 = ρ2gV2 acting through G2 , the centroid of V2

, Total upthrust = ρ1gV1 + ρ2gV2

. The positions of G1 and G2 are not necessarily on the same vertical line, and the centre of buoyancy of the whole body is, therefore, not bound to pass through the centroid of the whole body.