Hi,

The Physics Help Forum not working today, at least not from my ISP, so this goes here. It's basically a math deal anyway:

The formula to calculate the force of a point of mass, let's call them planets, that results from its being gravitationally attracted by another point of mass is Newton's:

Where

is the force of the planet that results from the gravitational attraction exerted upon it by the other planet,

is Newton's gravity constant,

and

are the respecive masses of the planets, and d is the distance between them.

For simplicity's sake let's say all the planets considered are of the same mass, so we can write

instead of

.

Now, if I'm not mistaken, the formula for calculating the force of a planet resulting from the gravitational attraction of more than two planets is:

Where

is the force on the jth planet resulting from the gravitational attraction of the other

planets, and

is the distance between the jth planet and the kth planet.

My question is "where is the vector addition?" That is, when considering the force on one planet that results from the gravitational attraction of many other planets, we have to take into account not only the distance of the other planets from planet j but also their

position with respect to it (right?).