Video narration
Why doesn't a planet moving sideways fly away from the Sun? Think of a ball swung on a string: it moves forward while the string pulls inward, bending its path. For a planet, gravity is that inward pull-the centripetal force bending forward motion into an orbit. Kepler's laws say: elliptical orbits; equal areas in equal times, meaning faster near the Sun; and T2 ∝ a3. It doesn't escape: gravity pulls inward while it moves forward-so it keeps falling around the Sun.