A proposition well known to geometers

Abstract

This note describes laboratory experiment ♯13 in the liberal arts physics course Galileo to Newton and Beyond. The title of these experiment is Newton’s Collision Experiments with Pendulums. Newton described these experiments in his Principia (pp. 22–25). He used these experiments to provide experimental confirmation for his action-reaction law. The note focuses on a mathematical proposition which was well known to geometers at the time of Newton, that “the velocity of a pendulum body in the lowest point is as the chord of the arc which it has described in its descent.”