A little trebuchet help

Jaspworld

I'm looking for the physics behind a trebuchet. I know sort of the basics like the initial kinetic energy of the projectile is converted into the potential energy of the counterweight.
However, I also need information related to friction, centripetal acceleration (and rotational mechanics), and tension. I'm not very sure what these three thibgs have to do with trebuchet. Are there any formulaes? I'd really like to know because the project's due on wedneday!

Thanks in advance.