Doing the plank, letting yourself float on the water, it’s a pleasure to be savored. A little more, perhaps on vacations by the sea than on trips to the swimming pool. But why do we float more easily in sea water? It’s all about density.
You may have already noticed this. We tend to float better in sea water than in pool water. ” Because sea water is salty “, we answer easily to the one who wonders about this subject. Yes, but then, why do we float better in salt water than in fresh water?
This is Archimedes (287-212 BC), the Greek scholar, who gave us the answer a long time ago. When he discovered the existence of this vertical force, directed from the bottom upwards, which any body undergoes when immersed in a liquid. A force equal to the weight of the volume of displaced liquid. A force we know today as Archimedes thrust.
Thus, if an object is less dense than the water it displaces, it floats. This is, for example, the case of a tree branch hit by a river. On the other hand, if an object is denser than the water it displaces, it sinks. Like a stone.
The denser the water, the better you float
But back to the original question. Why do we float more easily in sea water? Let us first recall that the human body is not homogeneous. Our bones are much denser than water. Our muscles, a little more too. On the other hand, our fat is a little less so. And above all, theair that we have in our lungs is much less. This is why it is possible for us to float on water. By planking.
The density of the water is also important. This is where the answer to our question really lies. Because the salt water of the sea is a little denser than thepure water of the swimming pool. Quite simply because of the weight of the salt it contains. Remember that the density of fresh water is equal to 1. That of sea water is on average around 1.025. It’s hardly more. But enough to allow us to float better. So imagine with the density of the dead Sea — of which the salinity can exceed 30% compared to an average of 5% for the seas of the world – which rises to some 1,240!
It can be noted that the temperature of the water also influences its density. The hotter it is, the lower it is. It is therefore in the waters of the sea not only the saltiest, but also the coldest that one floats most easily.
And did you know that the women float generally a little better than men? Because their bodies are naturally made up of slightly more fat than men’s. Fat slightly less dense than water. Fat fairly well distributed also, in the thighs, buttocks and chest. What to definitely ensure a better buoyancy.
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