where, for the i th body, ω ω i ∈ ∈ R 3 is the angular pre-collision velocity, ω ω ′ i ∈ ∈ R 3 is the angular post-collision velocity, I i ∈ ∈ R 3 × × 3 is the inertia tensor in the world frame of reference, and r i ∈ ∈ R 3 is offset of the shared contact point p from the centre of mass.