May I remind people of a bit of maths: A radian is the angle subtended by an arc of length X drawn along a curve of radius X. d/dx (sin(x)) = cos(x) if x is in radians.
Sin(x) = x - x^3/3! + x^5/5! - x^7/7! ... where x is expressed in radians. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of James R. Frysinger Sent: 23 March 2009 22:59 To: U.S. Metric Association Subject: [USMA:44083] Re: radians Good job on the subject line, Bill; I often forget to do that. I don't think that radians are going to go away in either of our lifetimes. It's one of the derived units that physicists and many engineers are fond of. Most certainly I do not agree with "degree velocity" or "radian velocity". That confounds unit and quantity names, rather like saying "meter height" or "hertz frequency". Jim Bill Hooper wrote: > > On Mar 22 , at 2:47 PM, James R. Frysinger wrote: > >> So if I say, "The motor is running at >> 8600/s" what do I mean? Better to say, "The motor is running at a shaft >> rotation rate of 8600/s" or "The motor is running at an angular velocity >> of 8600 rad/s", whichever is the case. Of course those differ by a >> factor of 2 pi. > > I agree with this (above) and would further argue that, if we indeed do > insist on naming the measured rate by proper names like "rotation rate", > "angular velocity" etc. then it should be possible to see that rotations > are not units and the, correspondingly, neither are radians. > > (Since degrees per second are also used for angular velocity, one would > need different names for these two things. I'd suggest "degree velocity" > and "radian velocity".) > > Abandoning the practice (built firmly into SI) of treating the radian as > a unit would, in my opinion, be progress. > > Regards, > Bill Hooper > Fernandina Beach, Florida, USA > > PS And I remembered to change the subject on this as I go off on a tangent. > > ========================== > Make It Simple; Make It Metric! > ========================== > > > -- James R. Frysinger 632 Stony Point Mountain Road Doyle, TN 38559-3030 (C) 931.212.0267 (H) 931.657.3107 (F) 931.657.3108
