[cocos2d-iphone] Chipmunk gravity problem

I'm looking for a solution for my problem.

I have a space with gravity and I need to add a shape to the space.
But the gravity should not affect this shape. It's not possible to set
the gravity to zero cause some shapes should fall under the effect of
gravity.

How can I do that?
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Did you read the cocos2d documentation? http://tinyurl.com/b8cqm3
Please, read it before asking for help. Probably your answer is there.
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