The Principles of Mechanics and Simple Electrodynamics Using the M.K.S. System

Abstract

Mechanical engineers in Britain have, in the past, tended to prefer to use the F.P.S. system of units when handling problems in mechanics. When one is dealing with hybrid subjects, such as control engineering, where problems in mechanics form only part of the subject, there are many disadvantages associated with the use of this system. For instance, engineers throughout the world have all now agreed to specify electrical quantities in rationalized M.K.S. units. Thus, when the electrical parts of problems in control engineering are always expressed in M.K.S. units, it becomes tedious and prone to error to be continuously converting to F.P.S. in order to solve the mechanical section. Apart from this, the M.K.S. system has real advantages for the mechanical engineer in his own field. In this system the units of force and mass are different and the confusion normally arising between the lb force and the lb mass does not exist. Furthermore the use of absolute units in the M.K.S. system does not bring about a unit of force which is too small for practical purposes (M.K.S. unit of force, i.e. the newton, is about a quarter of a pound force). Engineers never favoured the F.P.S. absolute unit of force, the poundal, because it was too small.