Page 189 - Handbook of Gold Exploration and Evaluation

164 Handbook of gold exploration and evaluation

Table 3.6 Calculated values of coefficient g at different latitudes

Latitude 0ë 10ë 20ë 30ë 40ë 50ë 60ë 70ë 80ë 90ë
ÿ2
g(ms ) 9.781 9.783 9.787 9.784 9.802 9.811 9.819 9.826 9.830 9.831

Table 3.6. For greater accuracy, using the base value g ˆ 9:781236 m/s, the
numerical value for g can be calculated at any desired location from the formula:
2
g ˆ 9:781236(1 ‡ 0.005243 sin L)(1 ÿ 0.000000097e) 3.4
where L is the latitude north or south of the equator, and e is elevation in metres
above sea level.
Most engineers, although recognising that geophysicists require extreme
accuracy, are usually content to assume a standard value of 9.781 for g and
hence constant body weights regardless of position. On sloping surfaces the
downslope component of force F d is given by:

F d ˆ Mg sin 3.5
where is the slope angle.
Gravitational forces increase as the sine of the slope and can be calculated for
any point on the sine curve, as illustrated in Fig. 3.14.

3.3.2 Water ± the processing medium
As a processing medium, water plays an important role in most weathering and
mass-wasting processes. Due to its high intermolecular attraction (melting
temperature 0 ëC, boiling point 100 ëC) water exists in all three physical states at
earth-surface temperatures: solid, liquid and gas. In its solid state, ice consists of
water molecules joined together by a regular arrangement of hydrogen bonds,
which apparently leaves empty spaces between the water molecules. The

3.14 The sine curve.