Galileo and Projectile Motion

By combining his work on falling objects with the concept of inertia, Galileo was able to understand how projectiles move. Prior to Galileo it was widely and erroneously believed that a projectile moved in a straight line until it lost a quantity called "impetus," at which point it dropped straight downward. By Galileo's time it was realized that a projectile instead followed a curved path, but no one knew what determined the curve.

By mathematical reasoning and clever experiments, Galileo showed that projectiles followed a parabola, a curve known to the Greeks. Later, Newton would show that the allowed paths in a gravitational field are a set of geometrical figures called conic sections, of which the parabola is a special case. Our modern understanding of projectile motion is essentially that of Galileo's.

Galileo and the Leaning Tower

Galileo made extensive contributions to our understanding of the laws governing the motion of objects. The famous Leaning Tower of Pisa experiment may be apocryphal: Galileo himself may not have dropped two objects of very different weight from the tower to prove that (contrary to popular expectations) they would hit the ground at the same time.

However, it is certain that Galileo understood the principle involved, and probably performed similar experiments. Many of Galileo's experiments demonstrating the properties of falling bodies were done by studying the motion of objects moving down a tilted surface or inclined plane. The realization that, as we would say in modern terms, the acceleration due to gravity is independent of the weight of an object was important for Newton's later formulation of a theory of gravitation.