Newton's First Law, also known as the Law of Inertia, 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 law explains that objects have a property called inertia, with more massive objects having more inertia and therefore being more resistant to changes in their motion. Newton's First Law describes how objects naturally resist changes to their state of motion.