From: spike66 (spike66@attbi.com)
Date: Fri May 17 2002 - 20:35:13 MDT
>
>
>On Tue, 14 May 2002, spike66 wrote:
>
>>Recall that Isp expressed in newton-seconds per kg.
>>
>Robert J. Bradbury wrote:
>"Recall"? I doubt that Isp was discussed in my high school
>physics class.
>
High school? Why Robert, you and I have worked on this
together. Did I halucinate that? {8^D
>Robert do get out of the sloppy habit of using seconds as a unit
>of specific thrust.
>
>
>Well, I think I've read either papers from JBIS or perhaps Mallove's
>"The Starflight Handbook" that always used seconds.
>
>Or am I simply mis-remembering things? Robert
>
No, they do this in some references. Still! The English unit is
pound force seconds per pound mass, which is shortened
to seconds. But a pound force doesnt cancel a pound mass,
so I have always disagreed with using that unit.
My solution all thru engineering school was to first convert
any english units to SI, do the problem, then convert back
to english. Another way to do it is to never use the unit
pound mass. Convert all pound mass to slugs, then work
the problem SI style, then convert the slugs in the solution
back to pound mass. If one does it this way consistently
one can partially undo the curse of the english unit system
and will not get answers that are mysteriously off by a
factor of about 32. {8-] spike
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