The Law of Inertia: How Understanding its History can Improve Physics Teaching

The law of inertia is a problem in teaching due to the impossibility of showing the proposition experimentally. As we cannot do an experiment to verify the law, we cannot know if it is correct. On the other hand, we know that the science based upon it is successful. A study in the history of mechanics has shown that there are different foundations for the law but also that the law plays the same role in the science since Newton. To avoid a statement of which we cannot be sure, the present paper proposes to understand the law through its function in the theory. In this case, we do not have to say how a free body moves, but rather that the rectilinear and uniform motion is the motion of reference in Newtonian mechanics.