Gravity and Motion: The Rules of the Cosmic Game

Why doesn't the Moon fall down, and what makes planets loop the Sun forever? The one rulebook that runs the cosmos.

You now know the scale of the universe and how we read it with light. This module hands you the single rulebook that choreographs all of it: gravity — the force that drops an apple, holds the Moon in the sky, swings the planets around the Sun, and binds entire galaxies together.

We open with a Zoom-Out Review to lock in everything so far, then live through one of the greatest stories in science: how humanity worked out that the Earth is not the center, then built — across Galileo, Newton, Kepler, and finally Einstein — a set of laws so powerful they let us weigh the Sun, steer spacecraft, and predict black holes. This is the module where the universe stops being a list of facts and starts being a machine you understand.

Zoom-Out Review 1 + The Revolution That Moved the Earth

First milestone review of Modules 1–2, then the night Galileo's telescope quietly demolished the Earth-centered universe.

45m

Newton's Big Idea: One Law for Apples and Planets

An orbit is just falling — and missing the ground forever. One law that covers the apple and the Moon alike.

45m

Kepler's Patterns: Why Orbits Are Oval and Planets Speed Up

Three laws, discovered with string, tacks and twenty years of stubbornness — and still used to weigh black holes today.

45m

Einstein's Gravity: Curved Spacetime, Escape, and Weightlessness

Gravity isn't a pull at all — it's the shape of space and time. Plus why astronauts float, and what escape velocity really means.

30m

What you'll carry out of this section

A refreshed grip on Modules 1 and 2, in the first milestone Zoom-Out Review.
The heliocentric revolution and the birth of the scientific method.
Newton's gravity — an orbit is falling sideways — and the inverse-square law.
Kepler's three laws, the cosmic ruler and scale that still weighs worlds today.
Einstein's curved spacetime, escape velocity, and why astronauts float.