Define gravitational field and find the strength of gravitational field due to mass M at a distance R?

Solution

The space around a material body in which it's gravitational pull can be experienced is called it's gravitational field.
The gravitational field strength at any point in the gravitational field is the force experienced by unit mass placed at that point.
Gravitational field strength is a vector quantity and is directed towards the mass causing the field.

At a distance R, place the test mass m at point P to find the gravitational field strength.
Force $space straight F with rightwards arrow on top$ experienced by the test mass m is,
   $straight F with rightwards arrow on top equals GMm over straight R squared$ , towards the mass M.
The gravitational field strength due to mass M at observation point P is,
$space space space space straight E with rightwards arrow on top equals fraction numerator straight F with rightwards arrow on top over denominator straight m end fraction equals GM over straight R squared$ , towards the mass M.