Kepler's laws – building an orbit from position and velocity

PhysicsGravitation & AstronomyAges 16–17

Four screens: First Law (drag the planet's position and velocity directly, the ellipse is recalculated instantly, and you can draw it with pins and string), Second Law (divide the orbit into equal time intervals and measure the area of each sector), Third Law (add your own points to a graph of T² against a³ and compare with real planets) and Lab (change the star's mass and run several planets at once). If the speed is too high the orbit is open, and the sim says so clearly instead of drawing a wrong ellipse. Based on the "Kepler's Laws" simulation by PhET Interactive Simulations, University of Colorado Boulder (CC BY 4.0); rewritten.

Lesson: Gravitational fields and planetary orbits