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BUG using units (I think)

javierarantegui
Tue, 15 Nov 2016 16:10:11 GMT

Hello, I was trying to do a calculation when I found the following problem. It happens using the latest versions of Calca for Mac and iOS. First, I define some constants: --- D = 5 µm in m => 5e-6 m r = 8 cm in m => 0.08 m v = -8 cm/2 s in m/s => -0.04 m/s ρp = 900 kg/m^3 ρf = 1000 kg/m^3 mu = 1e-3 kg*m/s^2/m^2*s --- Then, I try to do this calculation: --- (v*18*mu/(D^2*r*(ρp-ρf)))^.5 => NaN*i/s --- and I get this error. But, if I do the same calculation by parts, it works: --- a = v*18*mu => -0.0007 kg/s^2 b = D^2*r*(ρp-ρf) => -2e-10 kg c = a/b => 3,600,000/s^2 c^.5 => 1,897.3666/s --- If I try to take a shortcut, the same error: --- (a/b)^.5 => NaN*i/s --- Maybe it isn't a bug and it's me making a silly mistake I can't find. Javier