i am having a problem understanding lbm and lbf please help?

Answer 1

In the metric system we have separate units for mass (kilogram or kg) and force (Newton or N), but sometimes use the kg as a unit of the force we refer to as weight. 1 kg mass weighs 1 kg (force).
In the English system, we have separate units for mass (slug) and weight/force (pound or lb), but in everyday life, and also for reasons of laziness or expediency, we use the pound as a unit of mass. (After all, we usually determine something's mass by weighing it.) When doing this we use, or should use, lbm or lb(m) for these references in technical applications, and for clarity use lbf or lb(f) when referring to force or weight. 1 lb(m) weighs 1 lb(f).
Another way to look at the two systems (and these exceptions) is:
In metric, 1 N force accelerates 1 kg by 1 m/sec^2, and 1 kg of weight or force accelerates 1 kg by 9.807 m/sec^2 or g.
In English, 1 lbf accelerates 1 slug by 1 ft/sec^2, and 1 lbf accelerates 1 lb(m) by 32.17 ft/sec^2.