![]() This allows an assessment of the uncertainty in the measurement. The measurement should be repeated many times to arrive at a good average value, and, most important, to observe the scatter in the results. This makes a little more sense: force applied to the fluid, acting for some length of time. How does it relate to flowing liquids? One way of looking at it is to realize that pressure is force per square area. Viscosity is measured in units of Pa s (Pascal seconds), which is a unit of pressure times a unit of time. This makes the denominator small, so the answer (viscosity) is large. This equation makes sense in that spheres that fall slowly have low velocities. V = velocity = d/t = (distance sphere falls)/(time of it takes to fall) ![]() The formula for determining the viscosity is impressive, decorated with Greek letters and a squared term, but simply amounts to multiplying some numbers and then dividing by some others:ĭelta p = difference in density between the sphere and the liquid Thus, you know distance and time, so you also know velocity, which is distance/time. This is accomplished by dropping each sphere through a measured distance of fluid and measuring how long it takes to traverse the distance. The measurement involves determining the velocity of the falling sphere. If the fluid has a low viscosity, it offers less resistance to flow, so the ball falls faster. This makes sense: if the fluid has a high viscosity it strongly resists flow, so the sphere falls slowly. The faster the sphere falls, the lower the viscosity. This exercise uses one of the oldest and easiest ways: we will simply see how fast a sphere falls through a fluid. There are many ways to measure viscosity, including attaching a torque wrench to a paddle and twisting it in a fluid, using a spring to push a rod into a fluid, and seeing how fast a fluid pours through a hole. As expected, hawaiian volcanoes erupt more fluid lavas (called basalt) than do the Cascade volcanoes, which erupt a lava called andesite. Thus, shield volcanoes like we have in Hawai'i have gentle slopes (less than 10 degrees), while stratovolcanoes like the Cascades in the northwestern mainland are much steeper (roughly 25 degrees). ![]() Also, the more viscous the magmas a volcano erupts, the steeper the volcano. The more viscous the magma, the fatter the lava flow. Viscosity also affects the shapes of lava flows and the mountains they erupt from. On the other hand, when more viscous (higher viscosity) lavas do erupt, they usually do so explosively. The more fluid a magma, the more likely it is to erupt. In fact, one of the major differences between styles of mashed potatoes is the viscosity of the starchy mass: some people like their potatoes running and teeming with milk and butter (they are fans of low-viscosity potatoes), while others like their potatoes drier and stickier, so they almost crack rather than flow (these people are devoted to high-viscosity potatoes). For example, pushing a spoon with a small force moves it easily through a bowl of water, but the same force moves mashed potatoes very slowly. Viscosity is an internal property of a fluid that offers resistance to flow. ![]() To determine how fluid a liquid really is by measuring its viscosity. Teacher Page: Viscosity Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996
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