UNIT 1 : Physical Properties and States

UNIT I

Physical Properties and States of Matter, Mass, Weight, Volume, Density and Specific Gravity, Principle of Archimedes, Pressure Barometer.

Archimedes principle states that the buoyant force on an object is going to be equal to the weight of the fluid displaced by the object, or the density of the fluid multiplied by the submerged volume. In simpler terms, the weight of the displaced fluid is directly proportional to the volume of the displaced fluid (if the surrounding fluid is of uniform density).

This principle states that when a body (totally or partially) is immersed in a fluid, it appears to lose a part of its weight and the apparent loss of weight is equal to the weight of fluid displaced.

Apparent weight of body = Actual Weight of Body - Upthrust

= [mg - m / d x ρg]

= mg [1 - ρ / d]

where, d = density of body and

ρ = density of fluid.

It may be noted that buoyant force depends on the density of the fluid and not on the density of body acting on centre of gravity of fluid.

Archimedes Law of Floatation

The principle of floatation states that when a floating body like wood is placed in water, it sinks until the weight of water displaced by it is just equal to its own weight and then it floats. There are various situations that are to be understood.

When a body is immersed in a fluid then if

The weight W of body is more than the up - thrust W' (W > W'), the body will sink.

The weight W of the body is equal to up - thrust W' (W' = W), the body floats with whole of its volume inside the liquid.

The weight (W < W'), the body will float with some of its part outside the liquid.

When a block of ice floats in a liquid whose density is greater than that of water, the level of liquid will rise when all the ice melts into water. On the other hand, when an ice block floats in a liquid that have density less than that of water, the level of liquid will fall when all the ice melts into water. It may be noted that when an ice block floats in water, the water level will remain the same when all the ice melts into water.