Feynman's Lost Lecture: The Motion of Planets Around The Sun - Overview

Overview

You can explain to people who don't know much of the physics, the early history... how Newton discovered... Kepler's Laws, and equal areas, and that means it's toward the sun, and all this stuff. And then the key - they always ask then, "Well, how do you see that it's an ellipse if it's the inverse square?" Well, it's God damned hard, there's no question of that. But I tried to find the simplest one I could.

In a non-course lecture delivered to a freshman physics audience, Feynman undertakes to present an elementary, geometric demonstration of Newton's discovery of the fact that Kepler's first observation, that the planets travel in elliptical orbits, is a necessary consequence of Kepler's other two observations.

The structure of Feynman's lecture:

• A historical introduction to the material
• An overview of some geometric properties of an ellipse
• Newton's demonstration that equal areas in equal times is equivalent to forces toward the sun
• Feynman's demonstration that equal changes in velocity occur in equal angles in the orbit
• Feynman's demonstration, using techniques of Fano, that these velocity changes imply that the orbit is elliptical
• Discussion of Rutherford's experiments with scattering of alpha particles, and the discovery of the atomic nucleus

The audio recording of the lectures also includes twenty minutes of informal Q&A at the blackboard with students who had attended the lecture.