Q:

Sprite-Kit: Two different gravity vectors in one scene?

I'd like to have two objects in one scene, one which is pulled downwards, and one which is pulled upwards, but I can only specify one gravity vector which is applied to all objects in the physics world.
If there is no way to do this with gravity, how do I best go about it without it?

A:

All right, so I ended up doing what rickster proposed: regularly applying a constant vector to my objects.
    var pullDown = SKAction.runBlock({self.pullBirdDown()})
    var pullUp = SKAction.runBlock({self.pullBirdUp()})
    var wait = SKAction.waitForDuration(0.01)
    bird1.runAction(SKAction.repeatActionForever(SKAction.sequence([pullDown, wait])))
    bird2.runAction(SKAction.repeatActionForever(SKAction.sequence([pullUp, wait])))

