# RigidBody - fundamental question

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I'll get straight to the point: What is it I should work with when doing rigid body physics? The vertices that make up the body? Or just the center of gravity? Here's what I mean: Considering rotations: here the only thing that makes sense is to store some rotation values (angular velocity etc.) and apply them to all vertices of the body every frame (where everything rotates around the CG?) But what about translation? Say there was a collision with another object. I have the point of collision, the strength etc. What do I do then? Do I have to apply some force to the vertex that caused the collision? This would mean that I rather do particle dynamics having some constraints which connect several vertices to form a rigid body. Or is the whole body one thing? So that I only work with it's CG and ignore all vertices??? I'm sorry for my bad English here. But it's rather difficult to talk about these things because I don't really understand them (yet) ;-) Thanks for your help!!!

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The collision and physic systems are completely independent even if they are usually strongly connected. A body physic properties should remain coherent with that of the collision model (whatever it is, box, sphere, mesh or even a composite of all of these) to give plausible results.

What really matter are the physic properties of your body (velocities, inertia tensor, etc, etc) and the contact points that affect it each step.

As to what to do when you have a collision, it is a very generic question. I don't know your background and what you know on the subject but it might be a good idea to have a go at a particle-spring system (cf. the Jakobsen paper). Those are very easy to do (the basics at least, say a cube on a plane) and will give you a good feeling on what's happening.

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