Earth’s gravitational field Simulation
Earth’s Gravitational Field is a 3D interactive simulation built on Three.js that lets students explore how gravitational field strength varies with distance from Earth’s centre. It visualises five core concepts through toggleable layers: radial field lines with inward-flowing particles (showing force direction and density), concentric equipotential shells with hover-activated physics data (g, orbital speed, period, escape velocity), a satellite in an inclined low-Earth orbit, the Moon with correct tidal force arrows (stretch along the Earth–Moon axis, compression perpendicular), and a gravity well embedding diagram showing gravitational potential as depth. All values are derived from GM = 3.986 × 10¹⁴ m³/s².
Suggested Class Activity — “Escape the Well” (30 min)
Frame it as a mission planning challenge. Students work in pairs and are told: a new communications satellite must be placed in a useful orbit — but every kilometre of altitude costs fuel.
- Explore (5 min) — Students toggle Field Lines and Equipotential Shells, drag the view, and hover each shell. Ask: what happens to g as you move outward? Is the change linear?
- Record (8 min) — Students complete a table (Shell A–E): altitude, g value, orbital speed, period. These are all readable directly from the hover tooltips.
- Analyse (7 min) — Plot g against altitude on paper or a spreadsheet. Ask: what shape is the curve? What would g be at twice the radius? Prompt the inverse-square relationship: g ∝ 1/r².
- Decision (5 min) — Toggle the Moon and Gravity Well. Ask: where would you place your satellite and why? Students must justify using the Van Allen belt context from the tooltips (Shell B is inside the inner belt — radiation damage risk; Shell C is the slot region; Shell D/E are MEO).
- Share (5 min) — Pairs report their chosen orbit and reasoning. Discuss the real trade-offs: LEO needs less fuel but decays faster; GEO (not shown, at 35,786 km) is fuel-expensive but stays fixed.
Key GCSE links: gravitational field as a vector field, g = GM/r², equipotential surfaces (no work done moving along them), orbital mechanics (v = √(GM/r), T² ∝ r³), and escape velocity.