As already covered, the gravitational field
strength at a point in space is given by the force experienced by a unit mass
placed at that point, and gravitational field strength due to a point mass can
be easily calculated by the ratio of the force experienced by a test mass
placed at that point.
In case of an extended body to calculate
the gravitational field strength at any point in its surrounding, we consider
an elemental mass in the body and find the gravitational field strength at that
point due to this elemental mass, and integrate the result for the whole mass
of body. To understand this, see the video given below.
Using the above logic, gravitational field
strength due to various bodies can be calculated. There are several bodies
considered as standard bodies of which gravitational field can be calculated
using this logic, and are used in forming the basics of many fundamental
numerical problems. See the videos given below for gravitational field strength
due to some standard bodies.
Gravitational Field Strength due to a
Uniform Rod: https://youtu.be/ab61X9iQtcg
Gravitational Field Strength due to a
Uniform Ring: https://youtu.be/z42ypASf-Uk
Gravitational Field Strength due to a
Circular Arc: https://youtu.be/7TsMKbqOo4Q