![]() Viscosity is a measure of a fluid’s resistance to flow.įriction is defined as the resistance offered by the surfaces that are in contact when they move past each other. Both friction and viscosity exhibit the intensive property of the matter, as they remain the same even if the amount of the matter changes.ĭifferences between Fluid Friction (Viscosity) and Solid Friction: Viscosity.Both acts tangentially in opposite direction to that of motion.Both come into play whenever there is a relative motion.Similarities between Fluid Friction (Viscosity) and Solid Friction: The coefficient of viscosity of a gas is directly proportional to its temperature.The coefficient of viscosity of a liquid is inversely proportional to its temperature.Hence the coefficient of viscosity of a liquid is 1 decapoise or 1Ns m -2, if a tangential force of 1 N is required to maintain a velocity gradient of 1 s -1 between two parallel layers each of area 1 m 2. The SI unit of the coefficient of viscosity is Ns m -2 or decapoise or pascal second. Pseudoplastic: Pseudoplastic is the opposite of dilatant the more shear applied, the less viscous it becomes. Examples: quicksand, cornflour and water, silly putty. The behaviour of the fluid can be described in one of four ways:ĭilatant: In this case, the viscosity of the fluid increases when shear is applied. When shear is applied, the viscosity of non-Newtonian fluids decreases or increases, depending on the fluid. Non-Newtonian fluids do not follow Newton’s law and, thus, their viscosity (ratio of shear stress to shear rate) is not constant and is dependent on the shear rate. Examples: water, mineral oil, gasoline, alcohol The viscosity is independent of the shear rate. ![]() Newtonian fluids obey Newton’s law of viscosity. Water is an example of Newtonian fluid and toothpaste is an example of Non-Newtonian fluid. And, if the viscosity does change as stress or temperature changes, we describe something as being a non-Newtonian fluid. If the viscosity does not change with pressure, we describe something as being a Newtonian fluid. On increasing pressure viscosity of liquid molecules increases due to the increase in the resistance to the flow of liquid. The viscosity of liquids increase rapidly with an increase in temperature. Temperature and pressure affect the viscosity of a fluid. Thus car engine requires lubricating oil with a higher viscosity than lubricating oil required for the watch.Įffect of Change of Temperature and Pressure on Viscosity: Lubricating oils used in heavy machines is more viscous than those used in light machines.Blood circulation in our body depends on the viscosity of blood.The quality of fountain ink depends on the viscosity of the ink.This design work is called streamlining of the shapes and shapes themselves are called streamlined shapes. The shapes of bullets, arrows, racing cars, jet planes, bombs are such that opposition to their motion in air i.e. The body of fishes, the hull of ships, torpedoes, and submarines is such that the opposition to their motion in the liquid (water) is minimum.The Kinematic viscosity is the relationship between viscous and inertial forces in a fluid. Dynamic viscosity is the relationship between the shear stress and the shear rate in a fluid. There are two kinds of viscosity commonly reported, kinematic and dynamic. Gases also have viscosity, although it is a little harder to notice it in ordinary circumstances. A fluid with low viscosity flows easily because its molecular makeup results in very little friction when it is in motion. A fluid with large viscosity resists motion because its molecular makeup gives it a lot of internal friction. Viscosity describes the internal friction of a moving fluid.
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