## Thursday, May 17, 2007

### X-revision Upthrust in Fluids; Floatation and Archimedes’ Principle

When body is immersed in a liquid, the liquid exerts an upward force on the body. This force is called the upthrust or buoyant force.

What is upthrust or buoyant force?
The upward force exerted on a body by the fluid in which it is submerged is called the upthrust or buoyant force

Effect of upthrust: It is due to the upthrust that the weight of the body immersed in a liquid appears to be less than its actual weight.

The upthrust has the following two properties
(i) Larger the volume of the body submerged in the liquid, greater is the upthrust.
(ii) More the density of the liquid greater is the upthrust.

Bodies of average density greater than that of liquid, sink in it while bodies of average density smaller than that of liquid float on it.

What is Archimedes’ Principle?
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.

What is density?
Te density of a substance is defined as its mass per unit volume.

The relative density of a substance is the ratio the density of the substance to the density of water at 40C.

What is the principle of floatation?
According to the principle of floatation, the weight of a floating substance is equal to the weight of the liquid displaced by its submerged part.

What is a hydrometer?
A hydrometer is an instrument which is used for measuring the relative density of a liquid (heavier or lighter than water) directly and hence to test the purity of a liquid.

The length of the hydrometer immersed is inversely proportional to the density of the liquid in which it is placed.