   Body velocity after response
  Hello. I'm trying to write simple physics and met some problems that I can't solve for several days. Assume that rotated (but without angular velocity) 2d box fall on the ground verticaly. I have all information - contact point, collision normal, velocity etc. For example:V = [0; 5]ω = 0n = [0; -1]m = 10I = 30000r = [60; 30]I'm using formula for this situation (one of colliding bodies is static):.........-(1+e)(Vr • n)..j = --------------------.......1/m + (r × n)^2 / IVr = V + ω × r  - in my case it just V, because ω = 0 so ω × r = 0 too.AndV' = V  + j * n / mω' = ω + (r × n) * j / IBut I have wrong result - my box start to rotate on place, it's velocity on x always zero, but it should change after hit I think.My question is - what coordinates is r - in global or in local coordinates of my body? After hit velocity remains vertical - because j * n / m gives vertical vector too, but torque should move body in side.P.S.: sorry for so many words )P.P.S.: how to attach picture to topic?   
  Why would the x velocity be <> 0 ? the force is vertical and the reaction too (assuming the ground is flat and horizontal). The distance between the reaction vector and the c.g. will yield a rotation, but no X displacement, I think.   