In previous sections, you have mostly been using
The Particle Model: assuming objects act like point particles. A principal feature of this assumption is that the objects do not rotate. You will now relax this assumption to allow an object to rotate, but only if the entire object rotates with the same angular velocity. Such an object is typically known as a rigid body.
Assumption 5.9.1. The Rigid-body Model.
When you assume that a system can be treated as a rigid body, you treat it as undergoing both translational motion and rotational motion. Under this assumption, you treat all parts of the system as moving with the same angular velocity, while the center of mass of the object is treated as moving with the translational velocity.
