This web page is intended for instructors. Some of the experiments listed below also have "student web pages" which allow students to see movies of the experiments, but which don't have the descriptive details.
Introduction to Brownian motion and viscosityCoin flip activity: Students flip a coin. For heads they turn right and take a step, for tails they turn left and they take a step. They repeat this several times. Student web page: Students watch a video of Brownian motion of polystyrene particles, 1.9 micrometer in diameter, in water. They notice that the motion of the particles in video is very similar to their random walk motion. The student web page has this video clip. Web applet: Here is a link showing Brownian motion schematically: Einstein's Explanation of Brownian Motion Prepare for class:
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Brownian Motion & Viscosity LabMicroscopy: Students look at microscopy slides with polystyrene particles with diameters of 0.5 mm, 1.1 mm and 1.9 mm diffusing in water and water-glycerol mixtures. Student web page: Click here for web movies of Brownian motion, which may be useful if you don't have access to a microscope and/or particles with controlled sizes. Falling ball experiments: Students perform falling ball experiments. They measure the fall time of a glass sphere in glycerol and in water. Note that while the liquid's density does play a role (in changing the buoyant force on the sphere), with glass spheres this secondary effect doesn't change the results by much, as the density of glass = 2.6 g/cm^3 is much larger than the density of all of the liquids. In a more mathematically rigorous class, the velocity of the sphere can be measured and compared to the drag force, buoyant force, and weight of the sphere, to determine a value for viscosity. The Stokes drag force for slowly moving spheres is F_drag = 6 pi eta R v, with eta the viscosity, R the radius of the sphere, and v the velocity. For fast-moving spheres, this equation is not correct, but nonetheless can distinguish between the viscosities of these different liquids. Drainage experiments: Students time how fast it takes water, mineral oil, and glycerol to drain out of a plastic beaker through a 1/8" hole drilled at the bottom of the beaker. Viscosities of these liquids vary significantly whereas their densities are similar. Density plays a role in determining the hydrostatic pressure within the draining container, which causes the fluid to flow out, but the main influence on draining time is the viscosity. Prepare for class:
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Squishy Materials LabSquishy Materials: Students perform a set of experiments in four substances (we don't tell students what they are, we will tell them later). Click here to see a picture of the four substances:
Tools: We provided students with beakers, spatulas, spheres, microscopic slides - we do not tell them what experiments they should do. Instead we suggest some experiments that they can perform. Click here to see a picture of the experimental tools we provide for the students. Student web page: If you wish, the students can view movies of the various substances being stirred. As we suggest the students shouldn't know the names of the materials, on the student web page we list them as squishy materials 1 - 4. The materials are listed below, and all movies linked to below can be found also on the student web page.Details of squishy substances:
Prepare for class:
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Sand LabSand: During this lab students experiment with sand. Students receive a Lab Sheet with experiments that we would like them to do. These include studying the Brazil nut effect, and learning about the concepts of force chains. Student web page: Click here for movies showing these various phenomena. Prepare for class:
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JammingPrepare for class:
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