The law that describes an object's resistance to change in its motion is called:

The law that describes an object's resistance to change in its motion is known as inertia. Inertia is a fundamental principle in physics that states that an object at rest will remain at rest, and an object in motion will continue to move at a constant velocity in a straight line unless acted upon by a net external force. This property of matter directly relates to mass; the greater the mass of the object, the greater its inertia, making it more resistant to changes in its state of motion.

Understanding inertia is crucial in physics, as it explains why seatbelts are necessary in vehicles; passengers continue moving forward in the event of a sudden stop due to their inertia. This concept is integral to Newton's first law of motion, which formalizes the relationship between motion and forces acting on an object.

The other concepts listed involve different physical principles. Gravity is a force that attracts two bodies toward each other, momentum refers to the quantity of motion an object has (dependent on mass and velocity), and kinetic energy describes the energy an object possesses due to its motion. Each of these plays a role in motion and dynamics, but none specifically describe the resistance to change in motion itself, which is the essence of inertia.