Chris, I did and I am aware of the definition. The linking of a variable unit like force with a non-variable unit of mass, i.e., the Pound and the Kilogram was made necessary by the US refusal to adopt the SI system thus a multi-definition POUND needed to be defined in terms of a fixed definition KILOGRAM used by the rest of the world. However take note of the word in front of Pound. It is specified as a
Avoirdupois Pound. Avoirdupois is an Anglo-Norman-French pastiche which translates as "Goods of Weight". As the name implies Avoirdupois Pounds were employed to weigh
merchandise for sale.
To make this point very clear to students we had the old riddle question: "Which weighs more a Pound of Feathers or a Pound of Gold?" (Answer Feathers by a significant amount). Most today think that this is a trick density question and say that they are equal but in fact they are not. The question was used to drive home the difference between the
Avoirdupois Pound (merchandise) and the
Troy Pound (precious metals/diamonds/drugs).
So today in an effort to define a Cow in terms of Fish we enter into the new world order of Pound definitions:
The pound of force or pound-force (symbol: lbf) is a unit of force used in
some systems of measurement including English Engineering units and the old "Foot–pound–second system" (we also had and used at one time: a CGS system or Centigram-Gram-Second system and a MKS system or Meter-Kilogram-Second system). So in this new "simplified" system we have the "Pound-force" which is easily confused with "foot-pound", a unit of energy, or "pound-foot", a unit of torque( already easily confused), that is now written as "lbf⋅ft"; AND all of these should not be confused with the pound-mass (symbol: lb), often simply called "pound" (to add to the confusion), which is now taken as a unit of mass simply because it was defined in terms of a real existing mass unit, the Kilogram..
When a Pound was simply a POUND and a unit of FORCE the SLUG was the MASS unit so no confusion no disambiguation required. This new definition of lbf can be rephrased in terms of the old unit slug. A slug has a mass of 32.174049 lb. The new pound-force is the amount of force required to accelerate a slug at a rate of 1 ft/s^2
All of the questions above have revolved around the term PSI or Pounds per Square inch. Note Zippers original confusion in which Pounds as force as in PSI are confused with Avoirdupois Pounds as weight.
It is a simple concept: MASS is QUANTITY of matter and all MASSES are attracted to and by all other MASSES present in the universe. The attraction applies a FORCE to the MASSES which produces an ACCELERATED MOTION bringing the masses together. The MASS and the FORCE are directly proportionate to each other thus all MASSES accelerate towards each other at the same rate.
The Earth's gravitational field causes all MASSES (at or near the surface and neglect air resistance) to accelerate at 32.17 ft/s^2 or 9.81 m/S^2).
Thus an objects WEIGHT is a measure of the objects Gravitational field. Since different objects have different gravitational field strengths an OBJECTS WEIGHT is a variable quantity.
A column of air 1 inch by 1 inch by 100 miles or so is attracted by the Earth's gravitational field by a force giving the column a weight at or near the surface of 14.696 Avoirdupois Pounds. Since this Force is spread over a one square inch area we have PRESSURE defined as FORCE per unit of AREA thus 14.696 Avoirdupois Pounds per square inch of Area. Simply put PSI or I suspect to make things "simpler" 14.696 lbfsi.