SYSTEMS AND UNITS OF MEASUREMENTS

In absolute systems, the units of length, mass, and time are considered
fundamental quantities, and all other units including that of force are
derived.
In gravitational systems, the units of length, force, and time are considered
fundamental qualities, and all other units including that of mass
are derived.
In the SI system of units, the unit of mass is the kilogram (kg) and the
unit of length is the metre (m). A force of one newton (N) is derived as
the force that will give 1 kilogram an acceleration of 1 m/s2.
In the English engineering system of units, the unit of mass is the
pound mass (lbm) and the unit of length is the foot (ft). A force of one
pound (1 lbf ) is the force that gives a pound mass (1 lbm) an acceleration
equal to the standard acceleration of gravity on the earth, 32.1740
ft /s2 (9.80665 m/s2). A slug is the mass that will be accelerated 1 ft /s2
by a force of 1 lbf. Therefore, 1 slug 5 32.1740 lbm. When described in
the gravitational system, mass is a derived unit , being the constant of
proportionality between force and acceleration, as determined by Newton’s
second law.