as the gravitational force per unit mass that would act on a test mass placed at that point. So, generally,
throughout: a region of space
is: a vector field which gives rise to a gravitational force on a test mass placed at any point in the region. [P3.1]
is defined: at any point specified by a position vector as the gravitational force per unit mass that would act on a test mass placed at that point. So, generally,
where 
is the test mass. [P3.1, P3.2]
is related: to the gravitational potential by the requirement that it points in the direction of most rapid decrease of the potential, and has a magnitude given at every point by the magnitude of the rate of change of the potential (e.g. in the radial direction from an isolated point mass, so that 
It therefore always points in a direction at right angles to lines or surfaces of equal potential, and from high potential towards low potential. [P3.1, P3.2]
has as its SI unit: the newton per kilogram 
[P3.1, P3.2]
Copyright 1997, The Open University