title: SpriteKit: How to simulate magnetic force
body: <p>I am developing a game using iOS SpriteKit.  I am trying to make an object in this game that will pull things towards it and the force will get greater as objects come closer to it, think of a magnet or a black hole.  I've been having a difficult time figuring out what properties to change to get this nodes physicsBody to attract other nodes as they pass by.</p>