# How to calculate the resulting velocitys and rotation speed after two concave polygons collide in 2d

so I've been searching google for how to do this, but all anyone seems to care about is collision detection =p, and no results come close to teaching me how to calculate 2d elastic collision between two concave polygons.

I know how to solve elastic collisions between two 2d circles, but I can't find anything more complicated than that.

I'm also a very visual person, so it would be great if someone could show me how to do this or point me to a website! Thanks =)

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Concave or convex doesn't matter. The point about circles is the surface is always perpendicular to the vector to the CM, so there is no torque. The basic idea is to resolve the collision force into vectors through the CM of each body and perpendicular to the vector to the CM. The force through the CM accelerates the body. The transverse force changes the angular velocity around the CM. It sounds like in your case the bodies are rigid. In that case you can think in terms of impulse (which is the integral of force by time). Newton's $f=\frac{d(mv)}{dt}$ becomes $i_{\text{parallel}}=\Delta v/m$ and $i_{\text{perpindicular}}=\Delta \omega/I$