Gravitation is one of the four fundamental forces, governed by Newton's law F = GMm/r^2. The gravitational constant G = 6.674 x 10^{-11} N*m^2/kg^2 is universal, and the force is always attractive.

Gravitational field (E = GM/r^2) and potential (V = -GM/r) describe the effect of a mass on surrounding space. The field is a vector; potential is a scalar (always negative). At Earth's surface, g = 9.8 m/s^2.

g varies with height (inverse-square: g_h = gR^2/(R+h)^2) and depth (linear: g_d = g(1-d/R)). The approximation g_h ≈ g(1-2h/R) works only for h << R.

Escape velocity (v_e = sqrt(2gR) = 11.2 km/s) is independent of mass and direction. Orbital velocity (v_o = sqrt(gR) near surface) relates by v_e = sqrt(2)*v_o.

Kepler's laws govern planetary motion: elliptical orbits (1st), equal areas in equal times (2nd, angular momentum conservation), and T^2 proportional to r^3 (3rd). Satellite energetics: KE = GMm/(2r), PE = -GMm/r, Total E = -GMm/(2r).