So far, we’ve talked about the effects of a single gravitational field on a small mass in the field.

But in reality, there are lots of large masses around…… like stars…… planets…… and moons …… and all their gravitational fields overlap!

For instance, here are two stars.

At this point the gravitational field from this star points in this direction… 

… and the gravitational field from this star points in this direction.

The gravitational fields of the two stars are pulling in different directions.

So the overall gravitational field at this point is the vector sum of the two.

Next, at this point… 

… the gravitational fields both point in this direction

So the overall gravitational field is in this direction…

… and it’s stronger than the individual gravitational fields at that point.

Whereas at this point, the gravitational fields point in exactly opposite directions

… so the fields partly cancel out and the overall gravitational field strength is weaker.

And at this point, the individual fields completely cancel each other out, so the overall gravitational field strength is zero!

So, how do we calculate the overall gravitational field strength?

We’re going to look at that next.

But to sum up for now…

When a point is in two gravitational fields, the gravitational field strengths combine.

The direction and the magnitude of the individual gravitational fields combine, so we add the gravitational field strengths as…

The direction and the magnitude of the individual gravitational fields combine, so we add the gravitational field strengths as vectors.