title: Collision Normal in iOS7 SpriteKit Physics
body: <p>Does anyone know how to find or calculate the collision normal in SpriteKit. Coming from Box2D, there is a manifold  method that provides the normal information, but in SpriteKit framework, the SKPhysicsContact only provides a contact point.</p>
  
  <p>I am using primitive objects, plane colliding with circle, circle/rectangle collisions and circle/custom shape collisions.</p>
  
  <p>Could someone please point me to the Math on calculating surface normal using the collision contact point, that would be much appreciated.</p>