I've been looking into making 2D games with Unity. One thing which concerns me is the performance of the physics engine. Since Unity is a 3D game engine I'm going to have to assume it uses a 3D physics engine. Obviously I can turn this 3D engine into a 2D one by locking off various axis such that objects only move physically in 2D space.
However this worries me, for example Box2D being a specialized 2D physics engine is optimized for 2D. Would the physics in Unity3D be fast enough to say, duplicate the sorts of physics we see in games like Angry Birds on a handheld device?