Newton's First Law of Motion | Overview & Examples

This simple experiment demonstrates Newton’s First Law of Motion, or the law of inertia. When the sheet of paper is pulled quickly, the cup on top does not move along with it because of inertia—it tends to stay in its original position. As soon as the paper is gone, gravity takes over and pulls the cup straight down into the upright cup below. On the other hand, if the paper is pulled slowly, friction between the paper and the cup will drag the cup along, and the trick won’t work. This is the sa