OT: Speed of light

[Erik Max Francis]

Hrvoje Niksic wrote:

> It would be possible for US pound to only refer to weight, but I
> cannot find references to corroborate it.  For example, taken from
> Wikipedia:
> 
>     In 1958 the United States and countries of the Commonwealth of
>     Nations agreed upon common definitions for the pound and the
>     yard. The international avoirdupois pound was defined as exactly
>     453.59237 grams.
> 
> The "pound-force" wikipedia entry documents "pound" being used as a
> unit of force "in some contexts, such as structural engineering
> applications."

Then there's the even more fun and games in contexts where a distinction 
between mass and weight is not bothered to be drawn at all.  It's more 
common in practical engineering matters than pure physics; this is, for 
instance, why rocket motor performance (specific impulse) is measured in 
seconds, as it's the ratio of the the thrust (force) to rate of fuel 
usage (would be mass divided by time, but weight on Earth is used 
instead of mass).

Basically, physics rationalizations of Imperial/English/American 
(whatever you choose to call them) units are a total mess.

-- 
Erik Max Francis && max at alcyone.com && http://www.alcyone.com/max/
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