2002-03-27 What I meant was that a majority of the derived units are based on length, mass, and time. There are not that many that involve the other 4.
John ----- Original Message ----- From: "Barbara and/or Bill Hooper" <[EMAIL PROTECTED]> To: "U.S. Metric Association" <[EMAIL PROTECTED]> Sent: Wednesday, 2002-03-27 15:48 Subject: [USMA:19105] Re: watt seconds > on 3/26/2002 6:16 PM, kilopascal at [EMAIL PROTECTED] wrote: > > mechanical units form most of the base units for SI. > > It's of academic interest only, I suppose, but I disagree with the above. > > There are seven base units. One is electrical (the ampere), one is thermal > (the kelvin), one is chemical (the mole) and one is used in illumination > physics (the candela). That's four out of seven. > > Even if one accepts the suggestion that the other three (m, kg, s) are all > "mechanical" (which I don't*), it is not accurate to state that "most" of > the base units are mechanical. Three out of seven is not "most". > > Regards, Bill Hooper > college physics teacher (retired), USA (Florida) > > *P.S. > The other three base units are the kilogram, the second and the metre. Are > they "mechanical units? > > The kilogram is just as important in thermal physics and maybe even more > important in nuclear physics than it is in mechanical physics, so I don't > accept the suggestion that the kilogram is purely a mechancial unit. > > Many things vary with time, including the electric and magnetic fields in > electromagnetic waves (light, radio, etc.), transfer of thermal energy by > heat flow, radioactive decay, and others. Therefore, I don't accept the > notion that the second is purely a mechanical concept. > > Although the metre is certainly used in mechanical sense to describe > position and velocity, etc. (surely mechanical concepts) it is also used to > describe thickness of barriers through which heat, light, sound, ionizing > radiation, etc. may or may not pass and other things which are not > necessarily "mechanical". So I can't even bring myself to classify the metre > as a purely mechanical unit. > > +-+-+-+-+-+-+-+-+-+-+-+ > Do It Easy, Do It Metric! > +-+-+-+-+-+-+-+-+-+-+-+ >
