This lab involves "angular collisions" of the two disks on the same air pressure rig used in the torque and angular momentum lab. Students will relate angular momentum before the collision to angular momentum after the collision. They are also asked to relate kinetic energy before and after the collisions. They will make use of the equation for the moment of inertia of a uniform disk rotating through its center I=½mr2, the angular momentum L=Iω, and rotational kinetic energy K=½Iω2. They may need to be reminded that angular momentum can be positive or negative depending on the direction of rotation.