Kepler's Laws
Part of the Mechanics section of Coddy's Physics journey. Lesson 87 of 94.
First law: each orbit is an ellipse with the Sun at one focus.
Second law: equal areas in equal times, so the planet is fastest when closest to the Sun.
Equal areas in equal times: the planet is fastest near the Sun.
Third law:
T² / r³ = the same for every planet
In years and AU, T² = r³ for every planet of the Sun.
Challenge
Two moons orbit the same planet. The inner moon takes 2 days for one orbit, and the outer moon is 4 times as far from the planet. Measuring distances in units of the inner orbit (r1 = 1, r2 = 4), find the outer moon's period T in days.
Try it yourself
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Mechanics
1Vectors and Newton's Laws
Right TrianglesWhat is a Vector?Adding VectorsAxes and DirectionsVector ComponentsForces Around UsFriction and TensionNewton's First LawNewton's Second LawNewton's Third LawRecap - Net Force2Friction
What is Friction?Static FrictionKinetic FrictionFriction and Newton's LawsRecap - Sliding Crate3Inclined Planes
Forces on an InclineGravity ComponentsFrictionless InclineIncline with FrictionWill It Slide?Recap - Ramp Challenge6Projectile Motion
Independent AxesHorizontal LaunchLaunch at an AngleRange and Max HeightRecap - Hit the Target9Work and Energy
WorkKinetic EnergyWork-Energy TheoremGravitational PEConservation of EnergyPowerRecap - Roller Coaster12Impulse and Momentum
MomentumImpulseConservation of MomentumElastic CollisionsInelastic CollisionsRecap - Air Track15Simple Harmonic Motion
What is SHM?Mass on a SpringThe PendulumSHM GraphsEnergy in SHMRecap - Oscillator