DD.3.1 Deep Dive - Gyroscopes - Free Body Diagrams, Torque, and Rotating Vectors
DEEPTO CHAKRABARTY: A pivoted rod held horizontal, parallel to the ground, and released from rest will simply fall, rotating about the pivot point. In particular, suppose we have a mass attached to one end of a pivoted rod. So here is my pivot. Here's my pivoted rod, which we'll assume is massless. And I have-- and it has a length d, and I attach a mass m to one end. If I let this go from rest, it will simply fall, rotating about the pivot point, which I'll call s. And it's easy to understand that in terms of the action of gravity which is acting downward and the resulting torque about point s. If I replace this point mass with a wheel of the same mass, so this disk is a wheel with, let's say, a radius r and the same mass m attached to a pivoted rod. The rod is massless and has length d. If I hold this horizontal, parallel to the ground, and release it from rest, it will still just fall to the ground. Not a surprising result. What is surprising is if I...