Types of Masses and their Densities

As was pointed out earlier. Equation (1.6) allows us to find the attraction field everywhere, but it requires a volume integration, that in general is a rather cumbersome procedure. Fortunately, in many cases the calculation of the field g(p) can be greatly simplified. First, consider an elementary mass with density 6 q), located in the volume AV. Now let us start to increase the density and decrease the volume in such a way that the mass remains the same. By definition, these changes do not make a noticeable influence on the field because the observation point p is far away. In the limit, when 

we can reduce each elementary volume dV — hih2dl and increase the volume density so that the elementary mass  

It is clear that 6 q) tends to infinity as h, and we deal with the second mathematical concept of a mass. Respectively, the expression for the attraction field 

the field of attraction caused by volume, surface, linear, and point masses is 

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