These are Poiseuille’s law and the Couette viscometer. Hydrodynamics is a huge and very difficult subject (at least I think it is), but there are a couple of simple problems that, if nothing else, make good homework problems. The kinematic viscosity of water varies from about 1.8 centistokes (1.8 - 10 −6 m 2 s −1) at \(0 \circ \) C to about 0.3 centistokes (3 - 10 −7 m 2 s −1) at \(100 \circ \)C. The SI unit of kinematic viscosity is usually given simply as m 2 s −1, and 1 m 2 s −1 = 104 stokes. It is named after nineteenth century British physicist, Sir George Stokes, who made major contributions to diverse areas of physics. It relates to the internal friction within the fluid and determines how easily it pours or flows, with high viscosity meaning a thicker, slower-moving fluid and low viscosity indicating a thinner. The CGS unit of kinematic viscosity is the stokes (abbreviation St). Viscosity Meaning and Definition In English Viscosity refers to the measure of a fluid’s resistance to flow, or its thickness and stickiness. The dimensions of kinematic viscosity are L 2T −1. The ratio of the coefficient of dynamic viscosity to the density is the coefficient of kinematic viscosity, for which the usual symbol is the Greek letter ν. The dynamic viscosity of water varies from about 1.8 centipoise at \(0 \circ \) C to about 0.3 centipoise at \(100 \circ \)C. If, for a transverse velocity gradient of 1 m s −1 per cm, the tangential force per unit area is 1 N m −2, the dynamic viscosity is one decapoise. The SI (MKS) unit is the decapoise (also spelled dekapoise), though the SI unit the pascal second (Pa s), which is dimensionally correct, is also seen. That is to say, if, for a transverse velocity gradient of 1 cm s −1 per cm, the tangential force per unit area is 1 dyne cm −2, the dynamic viscosity is one poise. The unit is named after a nineteenth century French doctor, Jean Poiseuille, who was interested in blood pressure and hence in the rate of flow of liquids through tubes. The abbreviation for the unit is P – though it would be well to define it if you use it, since not everyone will recognize it. The CGS unit of dynamic viscosity is the poise. The dimensions of dynamic viscosity are ML −1T −1. The ratio of the tangential force per unit area to the transverse velocity gradient is called the coefficient of dynamic viscosity, for which the usual symbol is \( \eta \). Earlier in this chapter we discussed various types of rheological behavior and how to identify them. Viscosity is more easily measured than some of the properties that affect it, making it a valuable tool for material characterization. As a consequence of the transverse velocity gradient, the liquid below the dashed line will be dragged forward by the tangential force of the faster liquid above it, and the liquid above the dashed line will be dragged backward by the tangential force of the more sluggish liquid below it. Viscosity data often functions as a 'window' through which other characteristics of a material may be observed. There will be a transverse velocity gradient \(dv/dz\), with the liquid stationary at the river bottom, and the speed becoming faster as we ascend from the bottom. Send us feedback about these examples.\)Ĭonsider a river flowing over a smooth bed, as in Figure XX.9. These examples are programmatically compiled from various online sources to illustrate current usage of the word 'viscosity.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. 2023 Glucosamine helps in the formation and repair of cartilage, while chondroitin supports joint fluid viscosity, reducing joint strain and pain. Joanna Thompson, Scientific American, 22 Aug. 2023 Blood and saline solution have very different viscosities, meaning they are absorbed at different rates. Ying Xu, The Conversation, Its viscosity can change from person to person and even hour to hour. 2023 For example, in an episode about liquid thickness – or viscosity – Elinor and her friends try to get ketchup out of a bottle by shaking and squeezing it, but the ketchup remains stuck inside. 2023 Bacteria can also interact with the open bottle of wine, causing spoilage and changing the flavor and viscosity. Brittany Johnson, Verywell Health, 17 Oct. 2023 While one is not necessarily better than the other, the formulations will impact their texture, viscosity, and feel on the skin. Harry Guinness, Popular Science, 8 June 2023 This means that the flagellum has a fool-proof mechanism to enable swimming in low viscosity environments, which would otherwise be impossible for aquatic species. Recent Examples on the Web The different viscosities and densities affect how the propulsion system should operate, as well as the overall design of the drone.
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