Why the city like ship floats on the water? For the simple question, the simple answer is ship is less denser than water. Yes, really. The ship is designed and shaped so that it average density (mass/unit volume) is less than that of water. That is why the ship can only have ship-shape. But the usual explanation is based on Archimedes principle.
In this article, we are going to speak about density, even though it appears to be elementary concept, it has deeper meanings.
Density indicates how much matter is really packed in the unit volume. Common sense says, cotton package is lighter than a bar of iron. Physics says, mercury is 13.6 times heavier than water. That is, 1 cc of water weighs 1 gm. But 1 cc of mercury weighs 13.6 gm. Hence mercury is used in pressure-meters, thermometers etc,.
Osnium is the heaviest metal available in nature(density 22.6). Platinum, iridium, gold, silver are also heavy. Osmium and platinum are used in pacemakers and in artificial heart-valves.
The known lightest material is Aerogel. It is the gel like substance in which liquid is dried up and replaced by air. It is also called 'solid air', 'solid smoke' etc,.
Aerogel made up of graphene (carbon) is known as aerographen. It is very light. It's density is 0.16 milligram/cc and 7.5 times less dense than air. It can absorb up to 900 times its own weight in oil and water, making oil spill clean ups a potential application.
An atom has lot of empty space in which the electrons whirls around. All the heavy matters proton and neutrons are packed in the tiny nucleus at the center due to strong nuclear attractive force. Hence the nuclear density is highest and it is 2.3*10^17 kg/m^3.
When some stars run out of life, they collapse into a body of nuclei called neutron star. They are very dense and heavy and hence they have enormous gravity. Even the light that falls on it cannot escape, so they are also named black hole.
Astrophysicists say: Once the entire universe was contained in a tiny point that is like a dot at the end of this sentence. The point had infinite density. It is then exploded as the 'big bang' and the universe was born.
Some times we want to hear light music and read light stories. Sometimes we have to go for denser materials.
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