5.3 The acceleration due to gravity
In the absence of air resistance, an object falling freely under the influence of the Earth's gravity, close to the surface of the Earth, experiences an acceleration of about 9.81 m s−2 in the downward direction. The precise value of the magnitude is indicated by the symbol g and varies slightly from place to place due to variations in surface altitude, the effect of the Earth's rotation and variations in the internal composition of the Earth. Some typical values for the magnitude of the acceleration due to gravity, g, at various points on the Earth's surface, are given in Table 7.
Incidentally, one of the reasons that the value of g is well known across much of the Earth's surface is that extensive surveys have been carried out in which g has been accurately measured by timing the swing of very carefully constructed pendulums.
Table 7: The magnitude of the acceleration due to gravity at various points on the Earth's surface