Property of water that is of great importance is its high heat capacity and thermal conductivity. Heat of water is four times the heat capacity of air, water and thermal conductivity is 25 times more thermal conductivity of air. So a person in the water gives many times more heat than the air, and this may lead to a sharp chill.
Cooling the body increases with decreasing temperature. Water temperature is important for the swimmer. It defines the time allowed him stay under water and the type of gear that he wears for the slopes.
The sun's rays heat only the surface layer of water several meters thick. Deeper layers are heated by mixing warm and cold layers of water. At depths of 80-100 m water temperature remains constantly low (4-5 ° C) even in warm seas like the Black and Caspian, the sun's rays do not penetrate into these depths, and mixing occurs to a much lesser degree.
In water, sea salt solutions of various metals, mainly sodium chloride or table salt. Water lakes and rivers contain significantly less salt. Depending on the amount of salts dissolved in water changes its density. Everyone knows that swimming in the sea is easier than in the river, since the density of sea water at 2-3% greater than the density of fresh water.
Buoyancy - the ability of the body held
on the surface of water, or swim. Anybody immersed in a liquid displaces a certain volume and, accordingly, lose weight as much as it weighs expelled liquid (Archimedes). With regard to water, which share taken as a unit, we can say that a body immersed in water, loses weight as kilograms, how much of its volume in liters or cubic decimeters.
Thus, on a body immersed in water, there are two opposing forces: gravity, or body weight, which is directed straight down and tries to load the body into the water, and buoyancy force, directed vertically upwards, which tends to push the body of water. When gravity greater than the buoyancy force, the body has negative buoyancy, i.e., it will sink. If gravity is less than the force of buoyancy, the body becomes buoyant, i.e. it will float on the water surface. In case of equality of these forces the body will be like in zero gravity and have zero buoyancy, i.e., there will be neither sink nor float. |
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