On Sun, 17 Aug 2003 13:56:11 GMT, tad danley
wrote:

Roy Lewallen wrote:


I've tried to point out on this thread that although the feedpoint
impedance is an impedance with the units of ohms, and the impedance of a
plane wave in free space also has the units of ohms, they're not the
same thing.


This may not be a good analogy, but Specific Impulse of rocket motors
helps me to remember that the 'units' of something have to be considered
in the context of what is being measured. Specific impulse is a measure
of the performance of a rocket motor. It measures the thrust obtained
from a single kilogram of propellant burned in one second. The 'units'
of Specific Impulse are seconds, but we're not measuring 'time'.

It is a bad analogy--for the simple fact that in SI, the proper units
of specific impulse are newton seconds per kilogram (N·s/kg), or the
equivalent meters per second (m/s).

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/