This paper deals with the factors that influence the weight of an object near the Earth’s surface.
They are: (1) the Earth’s gravitational force, (2) the centrifugal force due to the Earth’s diurnal
rotation, and (3) tidal forces due to the gravitational field of the Moon and Sun, and other solar
system bodies to a lesser extent. Each of these three contributions is discussed and expressions are
derived. The relationship between weight and gravitation is thus established in a direct and
pedagogical manner readily understandable by undergraduate students. The analysis applies to the
Newtonian limit of gravitation. The derivation is based on an experimental (or operational)
definition of weight, and it is shown that it coincides with the Earth’s gravitational force
modified by diurnal rotation around a polar axis and non-uniformity of external gravitational bodies
(tidal term). Two examples illustrate and quantify these modifications, respectively the Eötvös
effect and the oceanic …