Read Planets: Gravity Holds, Distance Sets the Year
Planetary motion is governed by gravity. Planets farther from the Sun generally take longer to complete one revolution.
Motion and force questions become simpler when direction, starting condition, time and the acting forces are marked first.
Keep the Sun, Earth and Moon positions separate
Position and motion create the observed pattern
Rotation explains day and night; revolution changes Earth’s position around the Sun. Eclipses and phases depend on the viewing geometry.
Name the force
Gravity is the attractive force between masses. It provides the inward pull that continually bends Earth’s motion into an orbit around the Sun.
Order orbital periods
For the planets, a greater average distance from the Sun means a longer revolution period.
OlympIQ exam lens
- ✓Distinguish rotation from revolution.
- ✓Use gravity for orbital motion.
- ✓Order planetary years from farthest to nearest.
A planet’s day comes from rotation; its year comes from revolution. Do not exchange the two.
Ready to try the pattern?
100% coverage across the 2 linked questions.
Practise 2 linked questions