Newton's First Law states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. The First Law also introduces the concept of inertia, which is an object's resistance to changes in its motion. Newton's Second Law explains that the acceleration of an object depends on the net force acting on it and its mass, with greater force or less mass resulting in greater acceleration. Newton's Third Law describes that for every action force between two objects, there is an equal and opposite reaction force.