This document discusses centrifugal force, inertia force, and inertia torque. It provides equations to calculate the maximum stress on rotor blades due to centrifugal force. It also describes how inertia forces on aircraft propeller blades produce a twisting moment, and provides equations to calculate the normal force, twisting force, and twisting moment on blade elements. Finally, it reviews the equations of motion that relate the sum of forces and sum of torques to acceleration and angular acceleration of a rigid body in plane motion, and the relationship between torque and moment of inertia.