## Sunday, August 28, 2022

### Rotation and revolution

- I reserve the word "rotation" for the rotation of a solid disk, or a spinning top, or a whirling sling. These are motions where all rotating points have the same angular velocity. Rotational motion obeys the radian rule.

- I reserve the word "revolution" for orbital motion. Since orbital motion obeys Kepler's Rule (not the radian rule), objects revolving at different radii, have different angular velocities.

- This means that, a formula such as $a=v^2/r$ which is valid for rotation will not be valid for revolutions.

- But Newton and his disciples assume that rotation and revolution are the same motion and they build their theory of orbital motion on this similarity. This is why they claim that orbital motion must be dynamical and forceful.

- But orbital revolution is circular inertia, as Galileo thought.