What is resistance to change in motion?

Resistance to change in motion is called inertia. The amount of inertia in an object is directly proportional to its mass; an object with greater mass has more inertia than an object with less mass.

Sir Isaac Newton's First Law of Motion, also called the "Law of Inertia," states that an object at rest stays at rest, and a moving object remains moving unless an outside force acts on the object. An object currently in motion does not come to a stop unless a force counteracts the motion; this force could be friction of the object against a surface or air resistance. An object can have several forces acting on it at one time, but the object only changes its motion if a net force exists.