Before talking about the properties of water, it is worth understanding the very concept of "water". It is a clear liquid, which in most cases has neither a characteristic color nor a smell. When water passes into another aggregate state, it forms derivatives, which are called ice, snow (solid states) or steam (gaseous state). It is believed that it covers more than 70% of the surface of planet Earth - these are all kinds of seas and oceans, rivers, lakes, glaciers and other hydrological objects.
Water is a strong solvent, which in natural conditions contains many mineral salts and various gases. If we talk about its physical properties, we immediately pay attention to the fact that when the ice melts, its density increases, while for other substances a similar process occurs exactly the opposite.
The main feature of water is viscosity. Viscosity itself is the ability of a substance (whether it is a liquid, gas, or solid) to resist while moving particles of a substance relative to each other. This characteristic can be of two types - volumetric and tangential. Volumetric viscosity is the ability of a substance to take a tensile force. It manifests itself when sound or ultrasound waves propagate in water. Tangential viscosity is characterized by the ability of a fluid to resist shear.
When scientists studied the viscosity of water, it was found that the resistance of a substance during stretching and shearing depends on the speed of particles of different layers of liquid. If a layer that moves faster acts on a layer moving slower, then an accelerating force is activated. If everything happens exactly the opposite, then the braking force begins to act. The above forces are directed tangentially to the surfaces of the layers.
According to Newton’s law, the formula τ = μ dυ / dn was derived, according to which the force of internal friction is proportional to the velocity gradient along the normal and the area of impact. If we attribute the friction force to an area that is equal to unity, then we obtain the shear stress in the liquid, which is indicated in the above formula.
There is also such a thing as kinematic viscosity of water. It denotes the ratio of the dynamic coefficient (μ) to the density of the selected fluid (ρ). In the form of a formula, this expression will look as follows: ν = μ / ρ.
The viscosity of water at different temperatures varies, that is, the values of its coefficients decrease with increasing temperature. Thus, the dynamic coefficient of viscosity of salt water will be slightly different from the coefficient of fresh. When calculating the indicator itself, the difference will fluctuate around 5%.
A few more formulas can be given, but this is of no use, since the main material was presented earlier. The viscosity of water, by definition, can change, not to mention the state of aggregation of a substance. This data is important in aircraft and shipbuilding and some other industries.
There is a special table for determining the viscosity of water under various temperature conditions. This material can be used not only in theory, but also in practice. The table shows the data with an interval of 5 degrees, starting from 5 and ending with 100 degrees, which greatly facilitates the life of teachers and university students when making calculations.
Another important indicator - the dynamic kinematic viscosity of water, the so-called second viscosity (volumetric) - is a characteristic of volumetric compression strain. It plays a significant role in the attenuation of sound and the reduction of shock waves.