Gravitational Energy
Part of the Mechanics section of Coddy's Physics journey. Lesson 88 of 94.
Far from the ground, mgh no longer works. A mass at distance r from the centre has:
U = -GMm/r
The zero is very far away, so U is negative everywhere else.
U climbs toward zero as r grows, and U · r is the same at every distance. Moving out takes the work ΔU = U2 - U1.
U is negative and climbs toward zero as r grows.
Challenge
A probe 2 planet radii from a planet's centre has a potential energy of -30 GJ (-3×10¹⁰ J). Find its potential energy U when it is 3 planet radii from the centre.
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 Force4Kinematics in 1D
Position and DisplacementVelocityAccelerationMotion GraphsEquations of MotionRecap - Braking Car16Gravitation
Law of GravitationGravity and AltitudeSatellitesKepler's LawsGravitational EnergyEscape VelocitySatellite EnergyRecap - Mission to Orbit2Friction
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