Archimedes’ principle class 9

Last updated on July 7th, 2023 at 11:17 am

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.

Applications of Archimedes’ principle

Archimedes’ principle and law of floatation can explain several phenomena. Here, is a list of a selected few.

• Designing ships that float
• Determining the density of fluids using hydrometers.
• Controlling how submarines move within the water.
• Designing life jackets that can keep the human body afloat.
• Measuring the volume and density of irregularly shaped objects.

Upthrust formula

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)

Apparent weight Formula

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

Apparent weight of a floating body (during floatation) Formula

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