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 October 12th, 2016, 10:52 AM #1 Member   Joined: Sep 2016 From: zambia Posts: 31 Thanks: 0 Dimensional Analysis Please help out with the following question on dimensional analysis.And if any notes are available on the same topic,please give them to me. a) In Vander Waals equation (p+a/v^2)(v-b)=RT where p is the pressure, v is the volume,R is the universal gas constant and T the temperature. what are the dimensions of the 'a' and 'b' ? b) The viscosity n of a gas depends on the mass m, the effective diameter d and the mean speed of the molecules v. Use dimensional analysis to find an expression for n
 October 13th, 2016, 03:27 AM #2 Senior Member   Joined: Apr 2014 From: Glasgow Posts: 2,156 Thanks: 731 Math Focus: Physics, mathematical modelling, numerical and computational solutions This should probably be moved to the physics sub forum a) This question can be answered by understanding that when adding or subtracting quantities, those quantities must have the same units. Therefore $\displaystyle \left[\frac{a}{v^2}\right] = \left[p\right]$ $\displaystyle \left[a\right] = \left[p v^2\right]$ and $\displaystyle \left[v\right] = \left[b\right]$ where the square brackets here denote "units of" b) To answer this one, we have $\displaystyle [\nu] = [m]^a [d]^b [v]^c$ so replace the quantities with their units and then find a, b and c such that the equation is balanced (basically using simultaneous equations) Thanks from skeeter and topsquark Last edited by Benit13; October 13th, 2016 at 03:33 AM.
 October 22nd, 2016, 07:30 AM #3 Member   Joined: Sep 2016 From: zambia Posts: 31 Thanks: 0 thanks very much sir

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### the viscosity n of a gas depends on the mass m, the effective diameter d and the mean speed of the molecules v . use dimensional analysis to find an expression for n

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