SL + HL (potential, energy and escape speed are HL)
D.1 Gravitational fields
Every mass pulls every other mass. D.1 turns that pull into a field: Newton’s law of gravitation, field strength g = GM/r², Kepler’s laws and orbits, and at HL gravitational potential (always negative), escape speed and the energy of an orbit.
The big idea in one minute
F = GMm/r² · g = GM/r² · T² = 4π²r³/GM · Vg = −GM/r · vesc = √(2GM/r)
Gravity is always attractive. The field strength is the force per unit mass on a small point mass; it falls as 1/r². For a circular orbit, gravity provides the centripetal force, which gives the orbital speed and Kepler’s third law. At HL the potential is the work done per unit mass in bringing a small mass from infinity; it is zero at infinity and negative everywhere else, and the field is minus its gradient.
Your path through D.1
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Concept builders
Begin every part of this topic with its concept builder: predict, test with the simulation, explain. Then read the notes, practise, and finish with the papers.
Concept builder: predict, test, explain
Three guided lessons with simulations: predict, test, explain. Done in class.
Core work
Gravitation notes
The full topic: worked examples, the markscheme words and the common mistakes.
Levelled practice
Levels 1–4 with hints and worked answers. Goal: a ★ at Level 2 in every topic. For a 6 or 7, get Levels 3 and 4 too.
IB-format practice
Timed papers with markschemes, done as homework or classwork. One attempt: your report goes to your teacher.
10-question quiz
10 questions, 30 minutes, one attempt. Your teacher gives you the answers later.
Extra help
Not a step: use these when you are stuck, or to revise.
Visual guide
13 figures you can move. Use them when an idea does not make sense.
Flashcards
48 cards for quick recall of definitions and equations. Good before a quiz.