Define viscosity
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Viscosity is the friction between the different layers of a fluid. If a certain force is applied to each plate, this generates a strain on the fluid. Thus, the fluid is viscous when its mechanical energy is not constant, just as the fluid is not viscous when it remains constant. This idea was explained by Newton through a law that bears his name. This law states that in a fluid the frictional stress applied in one direction is proportional to its velocity and this situation is measurable with a coefficient of viscosity. From a scientific point of view, the study of viscosity must be located in the area of fluid mechanics. Its other units are newton-second per square metre (N s m-2) or pascal-second (Pa s.) The dimensional formula of viscosity is ML-1 T-1. The SI unit of viscosity is poiseiulle (PI). In gases, this phenomenon occurs due to collisions between molecules. The definition of viscosity is as follows: Viscosity is a measure of a fluid’s resistance to flow. In liquids, viscosity is mainly due to the electrical cohesion forces of the molecules that form matter. In other words, viscosity is a resistance in the form of internal friction. This is a frictional force between adjacent layers of fluids. Some fluid substances exhibit some degree of internal friction and this phenomenon is known as viscosity. In everyday life the term viscosity has a certain meaning, but it can take on another according to its scientific explanation. Thus, when touching certain sticky and dense substances we can say that they are viscous. This is what happens with honey, some dairy products, mustard, some sauces or cosmetic products. Based on scientific criteria, viscosity is a law defined by Isaac Newton.