At the same time, the flow has to be smooth, even in cold weather. Decreasing friction helps preserve the car parts for longer, but the oil coating has to be thick enough. The importance of the correct viscosity value of oil is paramount because, on the one hand, the oil has to provide enough viscosity to coat the metal surfaces that touch and decrease friction between them, and on the other hand, it has to flow well through the pipes. Meters that measure kinematic viscosity are also usually cheaper than those that measure absolute viscosity. Oil manufacturers prefer kinematic viscosity to absolute because it provides them with more accurate measurements. It is important to know the difference and not to confuse the two, because their values are not the same. Different devices are used for these measurements. Measures in these two situations happen differently, with the manufacturers measuring kinematic viscosity while the mechanics measuring the absolute one and then converting it to kinematic viscosity. The manufacturers test the viscosity before they sell the oil, and the mechanics measure the viscosity of oil before using it, to ensure that it fits the requirements. The oil used to lubricate machines is made with strict viscosity requirements, depending on which situation it is to be used in. Rheology is often concerned with studying both Newtonian and non-Newtonian liquids. Among other things, it studies viscosity, because viscosity determines in which manner the flow happens for different liquids. The study of the flow of matter, especially of liquids, is called rheology. Viscosity is a very important property and it is often used in daily life, especially for liquids. Honey behaves in this manner, becoming less viscous with vigorous stirring. For example, vigorous stirring will make some non-Newtonian liquids less or more viscous than they would be with a different amount of force applied during stirring. The viscosity of some other non-Newtonian liquids changes based on the stress over a given period of time. If, however, she simply stands on the surface, she will sink, because the force with which her soles push the liquid is smaller. If a person runs across a pool with this liquid, she will not sink, because she applies a considerable amount of pressure on the liquid. A mixture of corn starch and water has this property. Other non-Newtonian fluids, on the contrary, become more viscous when stress increases. High levels of stress make ketchup less viscous than low levels of stress - this is one of the effects that variable stress has on the viscosity of non-Newtonian fluids. However, applying a lot of force like shaking the bottle hard makes the ketchup come out. When it is in a bottle, applying a small amount of force to get it out is often futile. Non-Newtonian liquids deform at a different rate when the amount of shear stress changes - this rate can either increase or decrease with the increase in deformation, depending on the substance.Ī good example of a non-Newtonian fluid is ketchup. Fluids that deform at the same rate regardless of the force that causes this deformation are Newtonian. A distinction is usually made between two types: Newtonian and non-Newtonian fluids. Viscosity changes for different types of fluids. To remove most of the oil from the car, they run the engine to warm it up, increasing the flow of the oil. Decreased viscosity of oil with an increase in temperature is a very useful property for auto mechanics who change the oil. When measuring viscosity for machine lubrication purposes, it is commonly measured for 40° C (104° F) and for 100° C (212° F). When measuring kinematic viscosity, it is important to specify which temperature it was measured for, because it differs with temperature for each substance. It is calculated as absolute viscosity divided by the density. Kinematic viscosity measures this resistance, as relative to the density of the substance. Absolute Viscosity and Kinematic ViscosityĪbsolute viscosity, also known as dynamic viscosity, measures the resistance of a fluid to a force that is acting upon it to make it flow. The latter is more often used in the automotive industry. There are two types of viscosity: absolute viscosity that is used more commonly in medicine, cosmetics, and cooking, and kinematic viscosity. Viscosity is a measure of internal resistance of fluid to the force causing the fluid to flow.
This is what happens when a metal ball falls into a cup of non-viscous coffee
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