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Subject: Re: Units and Material Lib.
Author: Christopher Wright
Date: 1970-01-01 00:59:00

>I would like to have pressures
>entered as MPa, forces as N, and still have the model geometry be in mm.
>Has anyone dealt with this problem before?

Naming physical units after dead people is a confusing, isn¹t it? The secret is
to work with the most fundamental units-- length, mass, time--and express
everything else in those terms. The problem is that force and mass units are
defined in terms of each other since they're are related by the second equation
of motion--a Newton is 1 Kg-m/sec^2. That means if you use Newtons or Pascals
(another derived unit), meters are your length unit and all you need to
remember to affix E-3 to all your measured mm dimensions. I find this a huge
pain in the butt, and I try to use either Kg or Newtons throughout a problem
but not both.

My take is that trying to come up with a company-wide units base is a waste of
time--you're either going to upset the mm people or the Kg people or the Newton
people. Better spend the effort on making sure everyone knows the fundamentals
of dimensional analysis. Odd, how easy this works out in the inch-pound-second
system. It isn't pure but it really is 'nice.'

Christopher Wright P.E. |"They couldn't hit an elephant from
chrisw@s... | this distance" (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw

Posts possibly associated with message #125AuthorDateScore
119Re: Units and Material Lib.Brent Brower1999/01/055
120Re: Units and Material Lib.Markus Lengauer1999/01/05 
123Re: Units and Material Lib.Scott Reiss1970/01/01 
124Re: Units and Material Lib.Philippe Vidori1999/01/05 
125Re: Units and Material Lib.Christopher Wright1970/01/01 
127Re: Units and Material Lib.Alex Ng Siu Wai1999/01/05 
129Re: Units and Material Lib.Chris Rogers1999/01/06