What determines an object's inertia?

Inertia is fundamentally related to an object's mass. It is a property of matter that causes an object to resist changes in its state of motion—meaning an object with more mass will have a greater inertia compared to an object with less mass. This means that a heavier object requires more force to change its velocity (whether to start moving, stop, or change direction) compared to a lighter object. Consequently, mass directly quantifies how much inertia an object possesses.

The other factors listed—volume, shape, and material—do not define inertia in the same direct manner. While they can influence other physical properties of an object, they do not inherently affect the resistance to changes in motion like mass does.