Playbook
Gravitation
80 q - 1.75/paper - 23% HARD, and halved in 2025. Variation of g is 33 questions at 3% HARD — the page to keep.
- Questions in the bank
- 80
- q/paper (2024–25 papers)
- 1.75
- Tagged HARD
- 23%
- Subtopics
- 4
Strand: Long Tail
When you’ll see it
g at a height or a depth, a satellite's orbit or period, escape velocity, or the energy to move a body away from Earth.
How this chapter is tested
80 q at 1.75 a paper, 23% HARD — and it HALVED in 2025: 2.26 a paper across the 27 papers of 2023-24, 1.15 across the 13 of 2025. It is still set every year, so cut its hours rather than the chapter.
Keep one page whatever else you cut: Variation of g with Depth, Altitude, Density, and Latitude is 33 questions at 3% HARD. g at height h is g(1 − 2h/R) for small h; at depth d it is g(1 − d/R); at the centre it is zero.
The HARD is in the energy pages: Gravitational PE, Escape Velocity, and Energy (19 q, 42%) and Satellites (21 q, 29%). Escape velocity √(2gR) is √2 times the orbital speed near the surface, and a satellite's total energy is half its potential energy.
The sub-skills
The distinct skills inside the chapter, in the order to learn them.
Variation of g
Height: g(1 − 2h/R) for h ≪ R, g R²/(R + h)² in general. Depth: g(1 − d/R). g ∝ ρR at the surface.
Orbits
v_o = √(GM/r); T² ∝ r³ (Kepler). Geostationary period 24 h.
Energy and escape
U = −GMm/r; orbital E = −GMm/2r; v_e = √(2GM/R) = √2 v_o at the surface.
Traps to expect
Distractor shapes this chapter reuses. The Traps page covers the patterns that cut across chapters.
Using the small-height formula at large heights
g(1 − 2h/R) holds only for h ≪ R. At h = R, g is g/4 exactly, not zero.
Letting escape velocity depend on the mass or angle
Escape velocity does not depend on the body's mass or the direction of launch. Options that scale it with m are wrong.
Learn it before you drill it
This chapter has full teaching notes — foundations, worked examples, self-checks and a per-subtopic mastery checkpoint. Read the notes once, then drill subtopic by subtopic below.
Gravitation notesDrill every gravitation question
80 questions from the bank, scoped to 4 bundled subtopics.
Drill one subtopic at a time
The 4 subtopics this playbook covers, in catalog order.
Related playbooks
Often paired with this one — the technique, the trap or the taxonomy overlaps. Drill these next.