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I have a point at which there are (at least) two different forces (gravity to be precise) working. How do I combine those so that the force acting on the point are as realistic as possible?

To put the question into context: I have a small object which is attracted by two other large objects (that's the only direction I look at the problem, the large objects are not attracted by the small object). The force from that attraction is calculated by Newton's law of universal gravitation. So basically I have two vectors which represent those two gravitational forces. Currently I just sum those vectors up, but that seems kind of wrong.

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Assuming that when you say I just sum those vectors up you mean vector addition ( you are calculating the total force correctly. – John Rennie Aug 30 '13 at 15:09
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Why is your intuition telling you this is wrong? If it's just because it is "too easy", consider that often the simplest solution is the most correct - unless you have some physical argument against a simple solution that seems to work, don't dismiss it.

More specifically about your particular example, if I pull you to the left with a 100N force and someone else pulls you to the right with a 100N force, what do you expect will happen?

As John Rennie mentions in his comment, vector addition is exactly the way you should combine forces.

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That comes as a surprise. Then there seems to be something wrong in the way I display or store those vectors(it's only in part a physics problem). I really thought the underlying physics would be faulty. Thanks for the kind words of advice! – Brewer Gorge Aug 30 '13 at 16:27

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