“Why does a massive ship made of iron float, where as a nail made of iron sink in water?”. Rashmi looked at me inquisitively as soon as I asked this question.
We were on a boat cruise, taking a short break at Thames River at Windsor. I never miss a chance to showoff. “I never thought about that” she replied. I cleared my throat as I set about explaining it in one sentence.
“you see” I blurted out, “any object in water will float, if the weight of the water displaced by the object is less than the weight of the object itself”. She innocently stared at me. I was feeling like a High priest of Egypt, explaining the mystery of the pyramids to a common man.
“well, in simple terms” I continued, “say you are falling into the river now and your weight is 95 Kilos..” she threw a sharp look as soon as she heard this. “and if the water you displace in the river by falling into it is either 95 Kilos or more than that, you will float”. I continued ignoring her sharp glance. “In case of ship, the weight that ship displaces is much greater than the weight of the ship and thats why the ship floats in the water”, I concluded.
Obviously, million times smarter than me was Archimedes, who found this principle. Archimedes was an ancient scientist, who is famous for the episode of Eureka! He is supposed to have run naked to palace, when he found the principle of buoyancy.
ps: Many might think this as a silly physics thing, a thing which they have learnt in school. I also have learnt the same principle during my school days. But understanding of the principle is miles apart from having learnt the principle. Unfolding of the principles in natural worlds gives your mind a real boost. You begin to appreciate nature in a new way.