What happens to inertia when mass increases?

Inertia is the property of matter that refers to its resistance to changes in motion. It is directly related to the mass of an object; as mass increases, so does inertia. This means that an object with a greater mass will be harder to start moving if it is at rest and will also be harder to stop once it is in motion compared to an object with less mass.

When mass increases, the amount of force required to change the state of motion of the object, whether that be starting, stopping, or changing direction, also increases. This relationship is foundational in Newton's first law of motion, which states that an object at rest stays at rest, and an object in motion stays in motion unless acted upon by a net external force. Thus, with greater mass comes greater inertia, which makes sense intuitively: a heavy object requires more effort to move than a light one.

Therefore, when considering the relationship between mass and inertia, an increase in mass results in an increase in inertia.