Why does the air float

Aha : Why can you lie motionless on the water?

Ever since these colorful swimming noodles existed, more and more people have been floating motionless on the water in indoor pools. Carried, rocked, in search of the lost lightness of being. When I try to mark the “dead man” without such foam backing, instead of relaxing, I am constantly occupied with my unstable equilibrium. Although I'm considered slim, I don't stay up there easily. When swimming, it is not the weight that decides, but the density.

Even huge steel ships float. One liter of water has a mass of one kilogram, the same volume of steel weighs almost eight times as much. That's why a steel block goes under. But if the hull is hollow and has a lot of air in it, the mean density of the hull is less than that of the water. The steel colossus then floats just like a boat that we fold out of aluminum foil, while the same foil, crumpled into a ball, goes under.

More than two thirds of the human body is made up of water. It is therefore roughly the same density: anyone who weighs 75 kilograms has a volume of around 75 liters and can swim as well as dive in the water. Like a fish. Most bony fish have a gas-filled swim bladder, which they enlarge and shrink to regulate buoyancy. Increasing the volume of the body through inhalation can also help us to stay on top of the “dead man”.

In addition to the air in the lungs, the shape of the body and the distribution of muscles and fat determine the ability to swim. Muscles are heavier than fat, which floats on top at a density of around 0.9 kilograms per liter. Men usually have a significantly higher percentage of muscle than women, who put on a lot of fat on the hips, buttocks and thighs from puberty - presumably to meet the energy requirements during breastfeeding. It is therefore usually easier for women to mark the “dead man”, says Sigrid Thaller, biomechanic at the Institute for Sports Science at the University of Graz. But they are not completely flat in the water either. “The legs have a higher density than the torso.” The weight of the muscles pulls them down, one reason why they tend to move when swimming. The head, on the other hand, is lifted slightly out of the water, as desired.

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