A gravitational field is "a region in which masses will experience a force".

All masses attract - but unless you're huge it's a tiny force.

A non-uniform field. The further you are from the object at the centre of the field, the weaker the field.

Use Newton's Law of Gravitation to solve problems.

Always consider objects as point masses, all their mass concentrated at their centre.

The strength of a gravitational field is defined as the force, F, acting on a unit mass, m, in the field which in an equation is:

Symbol: g. Units: newtons per kilogram, Nkg^-1, which is the same as ms^-2.

Uniform field

In a uniform field, g will remain constant.

Radial Field

In a radial field, the field strength reduces as you move away from the centre.

Newton was the first person to fully explain gravitational fields. He came up with the following equation for field strength in a radial field:

where:

g = field strength at a point

G = the universal gravitational constant, value 6.7 x 10^-11 Nkg^-2m²

m =the mass of the object which causes the field

r = the separation between that point and the centre of the object causing the field.

If the field strength at a point in a field is the force per unit mass, it doesn't take a huge leap to realise that the total force acting on an object of mass, M, in a gravitational field will be

F = M.g

Apply that to the equation for field strength in a radial field to get: