On Tue, Apr 7, 2009 at 20:28, Fredrik Johansson <fredrik.johans...@gmail.com> wrote: > > On Wed, Apr 8, 2009 at 2:44 AM, Robert Kern <robert.k...@gmail.com> wrote: >> >> On Tue, Apr 7, 2009 at 15:18, flyeng4 <flye...@gmail.com> wrote: >> >>> In [40]: 1/s >>> Out[40]: 1/s <-- Makes sense but might be 'hz'? >> >> You need to be careful with that. Hz specifically means "cycles per >> second", which is not always the same thing as 1/s. In particular, >> angular frequencies are also measured in 1/s (technically radians/s >> but radians are a ratio of distances and so are "unitless" by the >> usual logic), but they differ from Hz by a factor of 2*pi. Sadly, >> units are not the most rigorous of mathematical constructs. > > I disagree, 1/s is the definition of the hertz, period (pun accidental :-).
Sorry, but that's just not true. There are other 1/s quantities that have nothing to do with cycles, like the becquerel: http://www.unc.edu/~rowlett/units/siderive.html > Frequencies and angular frequencies differ by a factor 2*pi precisely > because they measure different things, so equating them is (usually) > an error, like equating meters and kilometers. The inability of > dimensional analysis to prevent such errors is a limit of scope, not > one of rigor. The lack of rigor is that we use the same units to describe different quantities by silently dropping the "radians", "cycles", and "disintegrations". I entirely agree with you that they measure different things. We apply the same units to them regardless of that, and that is the lack of rigor I refer to. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "sympy" group. To post to this group, send email to sympy@googlegroups.com To unsubscribe from this group, send email to sympy+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sympy?hl=en -~----------~----~----~----~------~----~------~--~---
