Hello :) I was doing some problem and i don't quite understand it, so i thought you could help a bit. The problem is: rod with mass M floats in space and then it is hit at distance b (measuring from the end of the rod) by a small particle with mass m. Collision is elastic. I know how i should solve this. Energy, linear momentum and angular momentum are conserved. But i do t know how to explain for myself when we wrote for conservation of angular momentum: bmv=bmv1 + Mv2*l/2+Iω I understand the first and second parts on the right side of equation. The first one is angular momentum of particle right after the collision. The third is angular momentum of stick which rotates around the center of it's gravity, right? But what is Mv2*l/2. Why? i simply can t figure that out. If someone would explain it i would be really grateful. Thank you.