The acceleration is then:  a=F  =  Gm1

                            m2      r2

                                                          

                         (Nettleton, 1976)

                                       

Gravity meters are designed to measure variations in the weight or



force of gravitational attraction on a constant mass caused by



changes in the gravitational field.  These changes in the



gravitational field can be attributed to variations in density of



the subsurface materials.  It is lateral variation in this



gravitational attraction that will indicate the presence of



anomalous high or low density mass distributions.  Materials that



are more dense cause a stronger gravitational pull than those that



are less dense.  The unit of measurement for the acceleration of



gravity is called the gal and is equal to 1cm/sec.  The normal



gravitational acceleration on the surface of the earth is



approximately 980 gals.  Since we are measuring only small



differences in gravitational acceleration of the earth's field in



exploration, the milligal, which is equal to 1/1000 of a gal is



used.





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