of a particle is proportional to the resultant force 
that acts on it, and inversely proportional to its mass 
Thus, in terms of vectors,
describes: the amount of 'push' or 'pull' exerted on a particle which, if unopposed, causes it to depart from the uniform motion predicted by Newton's first law of motion. [P2.3]
therefore is: that which causes (or tends to cause) acceleration. [M5.1]
is: a vector quantity, so it has both direction and magnitude. [M2.4, P2.3]
is quantified: by means of Newton's second law of motion, which tells us that the acceleration of a particle is proportional to the resultant force that acts on it, and inversely proportional to its mass Thus, in terms of vectors,
or in terms of (scalar) components,
[P2.3]
has as its SI unit: the newton (N). [M2.4]
Copyright 1997, The Open University