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Tag: kinetic theory

  • Testing Granular Gas Theory

    Testing Granular Gas Theory

    When excited, a group of particles can behave much like a gas. These granular gases exhibit many similarities to molecular gases but contain one vital difference: without a constant input of energy, granular gases lose kinetic energy to collisions.

    Over the years, scientists have developed a special theory to describe the behaviors of granular gases, but most of its predictions could only be tested numerically. A new study used a microgravity experiment aboard a sounding rocket to physically test the theory.

    The experiment, shown above, consists of nearly 2800 magnetic particles, which the researchers could stir up using pairs of magnets. Once they shut off the magnets (which occurs at t=0 in the image above), the granular gas begins to “cool” as collisions sap away its energy. With this set-up, the researchers were able to confirm several key predictions of the granular gas theory. (Image and research credit: P. Yu et al.; via APS Physics)

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    Brownian Motion

    Have you ever noticed how motes of dust seem to dance around even in still air? The reason they do is because all the atoms and molecules in the air have a certain amount of random motion and all those tiny random motions result in collisions on the dust particles that shift them around. The technical term for this is Brownian motion, named for botanist Robert Brown who noticed through his microscope that particles of pollen floating on water moved constantly under no apparent force. The video above demonstrates the effect in 2D with vibrating brass particles representing atoms and a polystyrene ball as the pollen. Alternatively, you can see Brownian motion in the movement of nanoparticles in water. Although most areas of fluid dynamics do not explicitly consider the random motions of all these particles, the concept is fundamental to the nature of pressure and temperature, both of which are important quantities in fluid dynamics. (Video credit: Sixty Symbols; topic requested by just-a-random-nerd)

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    What is Pressure?

    Pressure is a critical concept in fluid dynamics – a driving force behind everything from weather patterns to lift on a wing. But where does pressure come from? Like many macroscopic forces dealt with in fluid dynamics, pressure can be traced to the effects of individual molecules within a fluid. Kinetic theory describes gases as a collection of small particles which are all in constant, random motion. These particles’ collisions with each other and with their container create a multitude of tiny forces, as in the demonstration in the video above. When all of these collisions are summed together, their net effect is expressed as pressure, a force per area. (Video credit: Sixty Symbols)