Moment of inertia, also known as rotational inertia, is a measure of an object's resistance to changes in its rotation. It plays the same role in rotational motion as mass does in linear motion. The moment of inertia depends on both the mass of the object and the distribution of that mass relative to the axis of rotation. The farther the mass is from the axis of rotation, the greater the moment of inertia. The SI unit for moment of inertia is kg⋅m².
The moment of inertia is defined as the product of the mass of each particle in a body and the square of its distance from the axis of rotation. For a simple point mass, the moment of inertia is I = mr², where m is the mass and r is the distance from the axis. For more complex objects, the moment of inertia is calculated by integrating over all the mass elements in the object. Flywheels are designed with large moments of inertia to smooth out variations in rotational motion. Spinning figure skaters decrease their moment of inertia by pulling in their arms to spin faster. In disc golf, discs are designed with most of their mass concentrated on the outer rim to increase the moment of inertia, making them more resistant to changes in spin.
