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answers:

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I'm trying to simulate a falling balloon in Box2DAS3. What is important is that balloon falls the such that the bottom part were you blow it up rotates towards the bottom if it's knock sideways or is dropped at an angle.

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I've tried offsetting the center of mass of the body and also joining two bodies together with the denser one representing the tie. In both cases the body falls at the same angle without rotating.

+3  A: 

An object in free fall (vacuum), without any initial linear or angular velocity, will never start to spin by itself, no matter where its center of gravity lies. You need to simulate fluid drag and buoyancy. A simple way to this is to add a small force on the top of the balloon that points upwards.

Cecil Has a Name
+1  A: 

Add a drag force to all objects. Something like -velocity / drag_amount

tm1rbrt
I've tried applying an upward force to the "body" but the motion is unconvincing. For example the balloon will fall with the bottom part when I'd like it to trend to the bottom.
Chris Porter
Make sure gravity is pulling from the center of gravity (maybe half way between the bottom and middle of balloon), and the drag force is pulling from the center of the balloon.
tm1rbrt