Null Point between Earth & Moon: This is the point on line joining the centres of Earth & Moon where the Gravitational Field is zero. See the example video below to understand finding the null point between two bodies:
Gravitational Field due to Subtractive Bodies: When from a
body one part is removed then the gravitational field at surrounding points
decreases due to the mass removed from the body. The below example videos
illustrates the gravitational field due to a sphere from which a spherical mass
is removed and a cavity is left:
Circular Motion under Gravitational Force : When point mass
revolves around another mass in uniform circular motion under its gravitational
force, then the necessary centripetal force required for the circular motion is
provided by the gravitational force only. See the example video on an
illustration on uniform circular motion under the gravitational field of a long
cylindrical mass: