We’re on a roll! The Physics of Rotation

Rotational Momentum and Energy Chapter 12

Key Concepts …  Rotating masses possess rotational energy and momentum  An object can have both kinetic and rotational energy  Moment of Inertia measures distribution of mass wrt CM  Two identical mass objects can have very different moments of inertia  Simple mathematical relationship links angular velocity to linear velocity as long as no skidding takes place

Important Analogies…  Mass – Moment of Inertia  Force - Torque  Momentum – Angular momentum  Kinetic Energy – Rotational Energy

What’s Moment of inertia…  It’s a natural extension of the concept of mass that accounts for how the matter in a body is distributed The “mass part”The “how it’s distributed” part

What’s Torque  It’s a natural extension of the concept of force

What’s Angular momentum  It’s a natural extension of the concept of linear momentum Moment of inertia Angular velocity

What’s Rotational Energy  It’s a natural extension of the concept of kinetic energy Moment of inertia Angular velocity

Going from the translational world to the rotational world…  Radian measure

How fast should the billiard ball from last week’s experiment have moved?  Just add a new type of energy term: