OK my little animation gurus,  I am making an animation that includes an anchored mine.  The chain links will have a positive density so will try and drag the mine down.   But the mine itself will have a negative density and more than counteract the pull of the chain.   Still with me?  

"Why bother with density" I hear you cry, well I want to add a flow force showing the current and want the chain and mine to act realistically. 

I can make the directional force go up rather than down, indicating the effect of the water, but then the chain wants to go up as well as the mine.    So, my question is:

 

How do I have two directional forces and apply objects to one or the other?

Or

How do I set certain objects to have a negative density ( I can't seem to do it with density)

Or

How should I be doing this?

 

A side question.   Why do my chains always break?!  How do I stop that?  Am I setting the force too strong (default) or the material too dense (metal)?

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Phillip Drawbridge
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