answers-01-18-2011

answers-01-18-2011 - Answers to Physics 176 One-Minute...

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Unformatted text preview: Answers to Physics 176 One-Minute Questionnaires Lecture date: January 18, 2011 What about those two pictures besides the Star Trek pic in the opening slide (picture of a mammoth and picture of a convecting fluid)? The mammoth picture will be explained at the beginning of next lecture, it is related to the idea of a relaxation time. The picture of stripes was a neat example I meant to discuss in class, of a simple but surprisingly rich non-equilibrium system known as Rayleigh- B enard convection that consists of a shallow wide layer of fluid that is convecting inside a cylindrical box whose floor is warm and ceiling is cold. You are looking down into the fluid from the top, the red stripes are regions where warmer fluid is rising (out of the plane of the image), the blue stripes are regions were cooler fluid is descending (into the plane of the image). Even though all external details of the box are time independent (temper- atures of floor, ceiling, and lateral walls are all constant), the fluid inside the box is capable of becoming time dependent with an intricate non-periodic dynamics called spiral defect chaos. If you click on the picture in my OpenOffice slide file, you will be able to see a movie of the spiral defect chaos state: how does a dumb fluid know how to produce such an in- tricate state when it is in contact with time-independent spatially uniform boundaries? How would one go about proving that certain properties can macro- scopically predict everything? One has to do many experiments and observe carefully what happens, it takes a lot of hard work and clever thinking. Historically, it took many decades for various people to start figuring out what is heat, what is tem- perature, and that gases were described by the equation P V = NkT which was the first clear demonstration that just a few numbers could characterize an equilibrium system. For example, you could fill a balloon with a known gas (say nitrogen or air) then try varying the temperature, pressure, number of particles, and kinds of particles in the balloon in many different ways and examine in each case what is the new state of the balloon. Many such experiments will 1 confirm that, if the system is in equilibrium to begin with and if you know three thermodynamic numbers of the system (say P , N , and T ), and then if you make various changes to the system such as increase P and decrease T , you can predict the values of the thermodynamic numbers that describe the system (say the new volume) provided that the final state is also an equilibrium state. What are common methods (or practical methods) for measuring the temperature inside a body? (Besides waiting) Several other students asked a similar question....
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This note was uploaded on 10/20/2011 for the course PHYSICS 176 taught by Professor Behringer during the Spring '08 term at Duke.

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answers-01-18-2011 - Answers to Physics 176 One-Minute...

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