Gravity Pitch

During the past two years, the Covid-19 pandemic has forced many colleges and universities to shut down. A similar situation occurred from 1665-1666, when an outbreak of bubonic plague struck London. Cambridge University was shut down and young Isaac Newton retreated to his family farm, where he began to formulate his ideas on calculus, optics, and gravity.

Most people have heard of Newton’s observation of a falling apple, but the key thought Newton had was to wonder, why doesn’t the Moon fall? Newton realized that the Moon was falling, but it was also moving sideways at the same time. This led Newton to realize that this simple combination of gravity and perpendicular motion could explain the orbits of the Moon and planets.

Students can model this thought experiment using the Gravity Pitch Gizmo. In the Gizmo, a giant “pitcher” stands on Earth’s surface, ready to fling an enormous ball. The harder the ball is thrown, the farther it goes before it lands, following a curved path. If the pitcher throws the ball hard enough, it goes all the way around Earth and hits the pitcher on the back of the head! This shows that only a single inward force is required to produce the circular path of the ball.