Gravitation

Force between two masses ∝ product of masses, inverse square of distance.

g decreases both with altitude and depth, for different reasons.

Minimum launch speed that lets an object escape gravity forever.

Speed at which gravity exactly provides the centripetal force.

Three laws of planetary orbits — ellipse, equal areas, T² ∝ a³.

Stored energy between two masses — zero at infinity, negative at finite separation.