Kepler S Third Law Law Of Periods — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Kepler's Third Law (Law of Periods) Applies to systems where one body is significantly more massive than the orbiting body (M >> m), such as planets orbiting stars or satellites orbiting planets. Assumes Newtonian gravity and non-relativistic speeds. Start with Newton's Law of Universal Gravitation: F g = G M m/r 2 Equate to Centripetal Force for circular motion: F c = m v 2/r Substitute velocity v = 2 pi r / T Rearrange algebraically to isolate T 2 on one side and r 3 on the other. Orbit must be closed (elliptical or circular). Mass of the orbiting satellite is negligible compared to the central mass. Believing the period depends on the mass of the satellite/orbiting body (it cancels out). Assuming 'a' is the distance from the surface rather than the center of mass.