REVIEW OF THE EARTHíS GRAVITATIONAL FIELD (continued)
The application of Newtonís Law of Gravity in the above example
is a little more complicated than it might seem for the
- Mass m on the Earthís
surface is attracted to every particle within the Earth.
Therefore, the attractive force W between object m and the
Earth (i.e., mís weight) is a vector sum of all of the
In the above example, object m
and M1 (a random particle within the Earthís sphere) have a
mutual attraction F. However, only the vector component of F.
(i.e. f) directed toward the Earthís center contributes to the
weight of object m. The summation of all these vector forces
mM2, ...... will compute the accurate weight of m. This is a
calculus problem for a mathematician.
- Another condition which
complicates the calculation of mís weight is the fact that
the earth is not a homogeneous sphere. The Earthís interior
consists of the crust, asthenosphere, transition zone, lower
mantle, outer and inner core, all consisting of materials of
- Also, the Earth is not a
perfect sphere. It is flattened at the poles and therefore,
the force of gravity is greater (i.e. an objectís weight is
greater) at the poles.
If object m could descend into
the Earth toward the Earthís center, its weight would decrease
until it became weightless at the Earthís center. As the object
descended from the Earthís surface, the Earthís mass above the
object would exert an attractive force tending to pull the
object toward the surface. The more powerful Earth centered
force would offset the surface directed force until the object
reached the Earthís center.
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