I'm working on a computer simulation, but I'm not sure how to approach this problem. I want to find the change in angular velocity on an object rotating on top of a flat plane. So far this is what I have: (* == multiplication not dot product) Ff x r = I * alpha Ff x r = I * dv/dt I can find I, Ff, and dt. I assume Ff x r can be reduced to Ff * r because the friction will always be perpendicular. I don't know what r is though, because the object is flat aren't there a ton of different particles experiencing the Ff? I'm I going to have to integrate all the little Ff x r? I'm pretty lost. Any direction would be wonderful.