Gravitation (Physics)

Recall cards on Newtonian gravity and its consequences. Newton's law of universal gravitation gives an attractive, inverse-square force F = G m1 m2 / r^2 along the line joining two masses, with the universal constant G first measured by Cavendish; spherically symmetric bodies act as though their mass sits at the center, and net forces add by superposition. Gravitation near Earth's surface: g = GM/r^2, weight W = mg, the fall of all masses at the same rate, and the small corrections from altitude, Earth's rotation, and its equatorial bulge. Gravitational potential energy U = -GMm/r (zero at infinity), conservation of total mechanical energy, escape velocity sqrt(2GM/R), and gravitational binding. Satellite orbits: circular orbital speed and period, orbital energy E = -GMm/2r, geostationary orbits, and weightlessness in free fall. Kepler's three laws of planetary motion (ellipses, equal areas, and the period-axis relation) and their basis in angular momentum and the inverse-square force. Tidal forces, spring and neap tides, tidal locking, and Io's heating. Finally Einstein's theory of gravity: the equivalence principle, spacetime curvature, the Schwarzschild radius and black holes, gravitational lensing, and time dilation.