1) The first law of motion states that if the net force on an object is zero, it will remain at rest or continue moving at a constant velocity. Another way to say this is that unbalanced forces are needed to change an object's velocity. 2) Inertia is the tendency of an object to resist changes to its motion. The greater the mass of an object, the greater its inertia. 3) Newton's second law states that acceleration depends on both the net force acting on an object and the object's mass. Acceleration is in the direction of the net force.