Every 76 years, Halley’s comet passes quite close by the Earth. At the most distant point in its orbit, it
is much farther from the sun even than Pluto. Is the comet moving faster when it is closer to Earth or
closer to Pluto?According to Kepler’s Second Law, objects that are closer to the sun orbit faster than objects that
are far away. Therefore, Halley’s comet must be traveling much faster when it is near the Earth
than when it is off near Pluto.
Key Formulas
Centripetal
AccelerationCentripetal
ForceNewton’s
Law of
Universal
GravitationAcceleration
Due to
Gravity at
the Surface
of a PlanetVelocity of a
Satellite in
OrbitGravitationa
l Potential
EnergyKinetic
Energy of a
Satellite in
OrbitTotal Energy
of a Satellite
in OrbitKepler’s
Third Law