A rigid body is usually modeled as a large collection of particles in a fixed arrangement. Being particles, they by definition have no size so they cannot undergo rotation about their own axes as that does not make sense. All kinetic equations for rigid bodies are derived from this model, and when a rigid body rotates about its own center of mass this rotation is accounted for by the revolving of the particles around the center of mass of the rigid body. Here is my problem in understanding: In reality the items (I use "item" to avoid confusion with the modeled particle) of which the body is composed have an angular velocity, the same as the angular velocity of the body as a whole. So these items have energy due to their own rotation It must be so that when you model the rigid body with items whose size approches zero, hence the number of items approches infinity, the contribution of energy due to their own angular velocity approaches zero. I don't understand why this is so, so if someone is able to show this would be greatly appreciated.