free course · live simulation
Learn gravity by flying through it
A free course built around a live, real-data solar system.
Explore orbits, tides and escape velocity in an interactive solar system, read the short explanation beside it and check yourself with a quiz.
- Level
- Beginner
- Length
- Self-paced
- Topics
- 54in 12 lessons
Gravity: a guided solar system. A slow loop through: The whole solar system; The rose that Venus draws; The Sun moves too — orbits are really helices; Orbital resonance: gravity keeping time. © 2026 Mateusz Wojczal. Earth texture: Solar System Scope, CC BY 4.0. Three.js (MIT). Inter and Roboto Mono (SIL OFL 1.1).
How it works
Look, read, check
Every module pairs the simulation with a short text and a quiz.
Explore the live simulation
Move through the solar system and watch orbits form from a few simple rules.
Read the short explanation
A few paragraphs per step, so you know what you are looking at and why.
Check yourself
A short quiz after each module shows what stuck.
Flight plan
Modules on their orbits
Work from the inner orbits outward: each module builds on the one before it.
12 lessons · 54 topics · about 7 h of material
Start · 10 minFree
Welcome
What the course is, how a lesson works and where the facts come from.
- Welcome to Gravity Lab
- Try the whole solar system
1 · 37 min
What gravity is
One rule between any two masses, and how it built the Sun and the Earth.
- Two masses
- Gravity builds the Sun and the Earth
- One rule for every scale
- Four ideas to recall
- Quiz: what gravity is
2 · 41 min
Falling around: orbits
Inertia, falling and missing, and what happens when a body goes too slowly or too fast.
- Inertia, and falling and missing
- Too slow, too fast
- An orbit is falling that keeps missing
- Practice: predict the path
- Quiz: orbits
3 · 37 min
Kepler's laws
Ellipses, equal areas and the link between a planet's distance and its year.
- The whole system on real orbits
- Venus and Earth draw a rose
- Three laws from the sky
- Kepler's three laws, step by step
- Quiz: Kepler's laws
4 · 32 min
Cosmic velocities
How fast a rocket must go to orbit the Earth, to leave it, and to leave the solar system.
- Falling back, orbiting, escaping
- Leaving the solar system
- Three speeds
- Three speeds at a glance
- Quiz: cosmic velocities
5 · 38 min
The Earth and the Moon
A moon that never falls, a shared centre, tides twice a day and a lumpy Earth.
- An orbit within an orbit
- Tides and the shape of the Earth
- Two bodies, one dance
- The barycentre and the tides
- Quiz: the Earth and the Moon
6 · 39 min
Orbits in 3D and a moving Sun
Tilted orbits, spinning bodies, a wobbling pole and helices through space.
- Tilts, spins and the North Star
- The Sun moves too
- Spin, tilt and helices
- The pole star over 26,000 years
- Quiz: orbits in 3D
7 · 52 min
The solar system as a machine
The speed of light, the magnetic shield, nested spheres of influence, Lagrange points and resonance.
- Light, wind and who wins
- Five parking spots
- Resonance
- Machinery of the system
- Practice: which Lagrange point?
- Quiz: the solar system as a machine
8 · 1 h 5 min
Travelling by gravity, and beyond
Gravity assists, the edge of the Sun's bubble, other worlds, the Milky Way and a galaxy with its motion stopped.
- Voyager and the gravity assist
- The edge of the Sun's bubble
- Other worlds and our galaxy
- What if everything stopped?
- A black hole and missing mass
- From a sling to a galaxy
- Voyager timeline
- Quiz: travelling by gravity
9 · 47 min
Einstein's gravity
Curved spacetime, Mercury's orbit, bent light, slower clocks, black holes and gravitational waves.
- Curved spacetime and Mercury
- Bent light and slow clocks
- Black holes and ripples
- Newton, then Einstein
- From 1915 to 2022
- Quiz: Einstein's gravity
Finish · 25 min
The final test
Fifteen questions across the nine modules. You need 70% and have two attempts.
- Final test
Finish · 10 min
Sources and licence
The references behind every number, the licence of the course text and how to reuse it.
- Sources, licence and attribution
In the course
Free, certified, in your browser
Everything is open in this demo.
Badge 1
Free
No payment and no card.
Badge 2
Certificate
A certificate when you finish the course.
Badge 3
Live simulation
Runs in your browser; a keyboard-usable text version of every step is included.
Data you can trust
Where the numbers come from
Planet and moon data comes from public NASA and JPL tables
Every figure shown in the lessons names its source
Course text is licensed CC BY 4.0, and the last lesson lists every source
Questions
Before you start
Is the course free?
Yes. Every lesson, quiz and the certificate are free.
Do I need a powerful computer?
No. The simulation runs in a modern browser. Every step also has a text version and a poster for devices without 3D or for reduced motion.
Is it only a video?
No. You move through the simulation yourself and each step is explained in text beside it.