Archimedes’ Principle

By Ameya

Category: physics

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Archimedes was a genius inventor and mathematician. He was a Greek and was born in Syracuse, Sicily around 286 BC.
He is famous for his framing of the Principle of Buoyancy, which he did in 212 BC. The Archimedes’ Principle states that, “ An object immersed in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the object.”
We all know that any object will feel lighter, when we immerse it in a liquid. This is because the water exerts an upward thrust on the object. The loss of the object’s weight is exactly equal to the weight of the liquid the object displaces on its immersion.

To visualize the phenomenon of fluid being displaced:

i) Take two empty cylindrical and inter-connected containers and name them “A” and “B”. Now fill container “A” with water. The level of the water in “A” should be just below the point of inter-connection.
ii) Take a medium sized ball and immerse it in the water.
iii) One can see that the moment the ball is inserted inside the water-filled container “A”, some amount of water spills out of the container “A” through the inter-connecting passage into the empty container “B”.

There is a mathematical formula with the help of which we can calculate the weight of the water displaced. We know that Weight = Mass x g. We can find out the mass of the water, which got displaced into container “B”, by multiplying the density of water with the volume of water in container “B”, as Mass = density x Volume. Hence, we can calculate the weight of the displaced water, as Weight = density x Volume x g.

If, instead of plain water, saline water were used, the ball would have displaced a greater weight of saline water than it did of plain water, and hence would have itself weighed lesser. This is because of the higher density of saline water than that of pure water. Thus, it is easier to float in a denser liquid. This is proved when it is easier for us to swim in the sea, than in a clear stream. Water in a swimming pool is also denser because of the diluted chemicals and makes swimming easier.

The upward force, which the liquid thrusts on the immersed object, is not related to the shape or weight of the immersed object. The upward thrust or the buoyant force only depends on the weight of the displaced liquid.
If the density of the submerged object is less than the density of the liquid in which it is submerged, the object will float. If the density of the submerged object is higher than that of the liquid in which it is submerged, the object will sink. If the density of the submerged object is exactly equal to that of the liquid in which it is submerged, then the object’s buoyancy exactly equals its weight and the object will neither float nor sink.