Gravitational fields

About this lab: Gravitational fields

Fly round a planet's radial field in 3D, read g and the potential off graphs, launch from the surface of a 3D potential well to find the escape speed, and compare the worlds.

The field around a mass, how g and the potential change with distance, and what it takes to escape

Gravitational fields is a free, browser-based simulation for Cambridge International AS & A Level Physics 9702 (topic 13 Gravitational fields). The course is assessed in Paper 1 (multiple choice), Paper 2 (AS structured), Paper 3 (advanced practical), Paper 4 (A Level structured) and Paper 5 (planning, analysis and evaluation). There are 5 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.

Syllabus coverage

• 13.1 Gravitational field: Gravitational field as force per unit mass; Representing fields with field lines; Uniform spheres as point masses at their centres; Newton's law of gravitation: F = Gm₁m₂ ÷ r². Lessons: Gravitational field and Newton's law.
• 13.2-13.3 Gravitational force between point masses and Gravitational field of a point mass: Circular orbits: linking gravitation and centripetal force; Geostationary satellites: 24-hour orbit above the Equator; Deriving g = GM ÷ r²; Why g is approximately constant near Earth's surface. Lessons: Orbits and field strength.
• 13.4 Gravitational potential: Potential as work done per unit mass from infinity; ϕ = −GM ÷ r and the meaning of the negative sign; Gravitational potential energy: Ep = −GMm ÷ r. Lessons: Gravitational potential.

Full syllabus map: A Level Physics 9702 topic 13.

How to use this simulation

1. 1. Field around a mass (3D).
2. 2. g and potential against distance.
3. 3. Potential well and escape (3D).
4. 4. Compare the worlds.
5. 5. Earth and Moon as a system (3D).
6. The buttons at the end of the tab strip give the scene the whole window (Full screen, Hide controls) and, on a dark stage, a projector-friendly palette (Light scene). Many scenes also have drag handles: drag them to change the set-up directly.

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