10.12 : Mass Moment of Inertia: Problem Solving

Knowing how to determine the moment of inertia in a wheel's axle can be invaluable in engineering and automotive applications. It provides an understanding of how changes in geometry, mass, and radius can impact its performance.

The axle can be approximated to a solid cylinder with longitudinal and perpendicular axes. Initially, a thin disc is considered parallel to the circular face of the cylinder.

This disc has its moment of inertia equal to one-fourth the product of mass and radius squared. The disc is located at a certain distance from the perpendicular axis. This allows using the parallel-axis theorem, which estimates the moment of inertia of the disc about its perpendicular axis.

The differential mass is expressed as the product of the cylinder's linear mass density and the disc's thickness.

The expression is then integrated over length to calculate the moment of inertia of the cylinder along the perpendicular axis through the centroid.

Furthermore, considering a thin cylindrical shell, the moment of inertia of the cylinder along its longitudinal axis can be estimated.

The differential mass of the shell element is substituted into the moment of inertia expression and integrated over the radius of the cylinder to get its moment of inertia along its longitudinal axis.

The moment of inertia expressions for both cases depends on geometric factors like the cylinder's mass, radius and length. The moment of inertia for a cylinder is simply another geometrical parameter. This formula allows engineers and designers to better understand their measurements in designing new products or fixing older equipment.