We’re ignoring for the moment excitation of internal modes of the molecules) That kinetic energy is conserved in each individual molecular collision (so At the same time, some slower molecules fly Molecules from the fast layer fly into the slow layer, whereĪfter a collision or two they are slowed to go along with the rest. So where does the gas viscosity come from? Think of two adjacent layers of gas moving atĭifferent speeds. Meters per second, the molecules have diameter around 0.35 nm, are around 3 orĤ nm apart on average, and travel of order 70 nm between collisions with other The previous picture of crowded molecules jostling each other is completelyĭetail later, the molecules of air at room temperature fly around at about 500 The first thing to realize is that at atmospheric pressure Returning to the two plates, and picturing the gas betweenĪs made up of layers moving at different speeds as before. Note first that, in contrast to the liquid case, gasĮven more surprising, it is found experimentally that over a very wide range of Liquids (not counting liquid helium -a special Maintain steady motion, but, not surprisingly, for gases anywhere nearĪtmospheric pressure the coefficient of viscosity is far lower than that for It is found experimentally that the equation F / A = η v / d still describes the force necessary to Suggested experiment, the two parallel plates with one at rest the other moving Michael Fowler Gas Between Parallel Plates Previous index next Viscosity II: Gas Viscosity
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