Archimedes’ principle and its statement and applications

Archimedes’ principle states that when a body is immersed partially or completely in a liquid, it experiences an upthrust, which is equal to the weight of the liquid displaced by it. This principle of Archimedes applies equally well to gases also. So the principle can be stated alternately as follows:

Archimedes’ Principle states that when a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displaced.

Application of Archimedes’ principle

Archimedes’ principle and law of floatation can explain several phenomena.

What is the expression of upthrust?

Upthrust = F = weight of the liquid displaced = Vρg where V = volume of the liquid displaced, ρ is the density of the liquid displaced, and g is the acceleration due to gravity.
(Note that, Vρ is the mass and Vρg is the weight of the liquid displaced)

What is the expression of apparent weight?

Apparent weight = Actual weight of the body in air – Upthrust

What is the apparent weight of the body which is floating? (during floatation)

During floatation, upthrust = actual weight of the body …(1)
As we know, Apparent weight = Actual weight of the body in the air – Upthrust …(2)
hence, from 1 and 2 in this floatation case, the apparent weight of the floating body = 0

Related study: Upthrust

Archimedes’ principle and its statement and applications
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