Doors in most homes rotate about hinges placed at one edge. Suppose you attempt to close such a door by pushing exactly at the hinge line rather than at the doorknob.
a. Explain in detail why this push produces no tendency for the door to rotate, even though a non-zero force is applied.
b. Describe another everyday situation where a force is intentionally applied so that it produces zero torque, and explain why this is useful in that context.