12/22/2023 0 Comments Viscosity chemistry definition quizlet![]() ![]() ![]() What does this picture have to do with viscosity? Well, in order to get that top plate to move, we have to apply some sort of force to it. There is an important quantity, called the strain rate or shear rate (given as a symbol the Greek letter gamma, γ, with a dot on top) that describes how the speed of the liquid moving along the x-axis (left to right) changes, layer by layer, in the y-direction. The arrow beside the layer is meant to convey its relative speed: the top layer is moving the fastest, the next layer is a little slower, and so on the bottom layer isn't moving at all. In the diagram, the symbol, u, stands for the speed of the layer of liquid. If we imagine that the liquid in between these two extremes is divided into very thin layers, then each layer must be moving at a slightly different speed than the next. ![]() So at one extreme, the liquid is moving along with the sliding plate and at the other extreme the liquid is perfectly still. There also ought to be some friction between the moving plate and the liquid that will make the liquid move along at the same speed as that plate. What happens to the liquid between the plates? There ought to be some friction between the stationary plate and the liquid that will keep the liquid still. One plate says still and the other one moves. One of the common ways of assessing properties in rheology is to place a sample between two parallel plates and move one plate with respect to the other. There's an element of force or pressure that comes into play here, too. Another very simple definition, attributed to chemical engineer Chris Macosko at University of Minnesota, is the study of "what happens when you squish stuff". Rheology is, literally, the study of flow. Viscosity measurements are the realm of a field of science called rheology. ![]()
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