5.4.1: Field of a Point Mass
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Equation 5.3.1, together with the definition of field strength as the force experienced by unit mass, means that the field at a distance r from a point mass M is
g=GMr2N kg−1 or m s−2
In vector form, this can be written as
g=−GMr2ˆrN kg−1 or m s−2
Here ˆr is a dimensionless unit vector in the radial direction.
It can also be written as
g=−GMr3rN kg−1 or m s−2
Here r is a vector of magnitude r − hence the r3 in the denominator.