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Old September 29th 03, 06:12 PM
Jim Kelley
 
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Gene Nygaard wrote:
My 'weight' is 230 pounds on earth. That's a fact.

My 'weight' would be 230 pounds on the earth's moon. That's also a
fact.


Your weight is defined as what you weigh on Earth, assuming a
gravitational acceleration of g. Obviously it's not true that your
weight would be measured as 230 pounds on the moon. The CRC Handbook of
Chemistry and Physics states that the weight of a body varies with
location, and defines weight as W = mg, where g is the local
acceleration due to gravity.

Reflecting the apparent dichotomy, the CRC defines the pound both ways:
"1. A unit of mass equal in the U.S. to 0.45359237 kg. exactly.
2. Specifically, a unit of measurement of the thrust or force of a
reaction engine representing the weight the engine can move, as an
engine with 100,000 pounds of thrust. 3. The force exerted on a one
pound mass by the standard acceleration of gravity."

Interestingly, they also define poundal, pound mass and pound weight.
No mention of pound force. Evidently, that would be redundant. ;-)

As an aside, what do you think: Will NASA ever learn the lesson of
the Mars Climate Orbiter, and quite using pounds?


Actually the contractor had specified the thrust of its rocket motor in
pounds. NASA failed to properly convert to the CGS system that it (and
most other scientific organizations) normally use.

73, Jim AC6XG