diff --git a/js/consts.mjs b/js/consts.mjs
index 15d11dc..081277e 100644
--- a/js/consts.mjs
+++ b/js/consts.mjs
@@ -7,3 +7,5 @@
 export const SECTOR_SIZE = 512;
 // Star count per sector.
 export const STAR_DENSITY = (SECTOR_SIZE ** 2) / 10000;
+// G, G-boy, The big G, Mr. G, g's big brother, G-dog
+export const GRAVITATIONAL_CONSTANT = 0.01;
diff --git a/js/data.mjs b/js/data.mjs
new file mode 100644
index 0000000..85039cc
--- /dev/null
+++ b/js/data.mjs
@@ -0,0 +1,32 @@
+export const modules = {
+	capsule: {
+		small: {
+			name: 'Small Capsule',
+			tooltip: 'A small, simple capsule. Provides just enough ' +
+				'rotational power for a small rocket.',
+			type: 'capsule',
+			mass: 2,
+			rotation: 0.1
+		}
+	},
+	fuel: {
+		small: {
+			name: 'Small Fuel Tank',
+			tooltip: 'A small flimsy tank with enough fuel for a short trip.',
+			type: 'fuel',
+			mass: 1,
+			capacity: 3
+		}
+	},
+	thruster: {
+		light: {
+			name: 'Light Main Thruster',
+			tooltip: 'Powerful enough to lift a small ship, but not much ' +
+				'more. Not very efficient.',
+			type: 'thruster',
+			mass: 2,
+			thrust: 10,
+			isp: 200
+		}
+	}
+}
diff --git a/js/game/events.mjs b/js/game/events.mjs
index 0ac2b52..bdccf45 100644
--- a/js/game/events.mjs
+++ b/js/game/events.mjs
@@ -1,5 +1,5 @@
 import * as game from './index.mjs';
 
 export function startGame() {
-	console.log('started');
+	game.changeView('game');
 }
diff --git a/js/game/index.mjs b/js/game/index.mjs
index df96860..f62296c 100644
--- a/js/game/index.mjs
+++ b/js/game/index.mjs
@@ -2,15 +2,15 @@ import * as graphics from '../graphics/index.mjs';
 import * as gui from '../gui/index.mjs';
 import * as assets from '../assets.mjs';
 import * as input from '../input.mjs';
+import * as world from '../world/index.mjs';
+import * as events from './events.mjs';
 
-export let game;
+export let state;
 
 export async function init() {
-	game = {
-		state: {
-			room: 'menu',
-			paused: false
-		}
+	state = {
+		view: 'menu',
+		paused: false
 	};
 
 	graphics.init();
@@ -18,6 +18,8 @@ export async function init() {
 	gui.init();
 	input.init();
 
+	//events.startGame();
+
 	// Recursive `requestAnimationFrame` can cause problems with Parcel.
 	while(true) {
 		await tick();
@@ -25,7 +27,17 @@ export async function init() {
 	}
 }
 
+export function changeView(view) {
+	state.view = view;
+	gui.changeView(view);
+
+	if (view == 'game') {
+		world.init();
+	}
+}
+
 async function tick() {
+	if (state.view == 'game') world.tick();
 	gui.tick();
 	graphics.render();
 	input.tick();
diff --git a/js/graphics/index.mjs b/js/graphics/index.mjs
index 73200de..633b84b 100644
--- a/js/graphics/index.mjs
+++ b/js/graphics/index.mjs
@@ -3,6 +3,7 @@ import {getContainedSectors} from '../world/index.mjs';
 import * as background from './background.mjs';
 import * as gui from './gui.mjs';
 import * as draw from './draw.mjs';
+import * as ship from './ship.mjs';
 
 export let canvas, context, tempCanvas, tempContext;
 export let view;
@@ -36,6 +37,7 @@ export function render() {
 	// TODO: Translate canvas.
 
 	background.render();
+	ship.render();
 
 	context.restore();
 
diff --git a/js/graphics/rocket.mjs b/js/graphics/rocket.mjs
deleted file mode 100644
index 474ccf4..0000000
--- a/js/graphics/rocket.mjs
+++ /dev/null
@@ -1,6 +0,0 @@
-import {canvas, context} from './index.mjs';
-import * as assets from '../assets.mjs';
-
-export function render() {
-
-}
diff --git a/js/graphics/ship.mjs b/js/graphics/ship.mjs
new file mode 100644
index 0000000..0f9cbae
--- /dev/null
+++ b/js/graphics/ship.mjs
@@ -0,0 +1,12 @@
+import {canvas, context} from './index.mjs';
+import * as assets from '../assets.mjs';
+import * as world from '../world/index.mjs';
+
+export function render() {
+	world.ships.forEach(renderShip);
+}
+
+function renderShip(ship) {
+	context.fillStyle = 'red';
+	context.fillRect(ship.x, ship.y, 10, 10);
+}
diff --git a/js/gui/index.mjs b/js/gui/index.mjs
index a2e8735..723f56c 100644
--- a/js/gui/index.mjs
+++ b/js/gui/index.mjs
@@ -20,6 +20,10 @@ export function changeView(view) {
 	if (view == 'title') {
 		root.append(modules.title());
 	}
+
+	if (view == 'game') {
+		root.append(modules.game());
+	}
 }
 
 export function measureText(msg, font) {
diff --git a/js/gui/modules.mjs b/js/gui/modules.mjs
index 64078da..1797c15 100644
--- a/js/gui/modules.mjs
+++ b/js/gui/modules.mjs
@@ -33,3 +33,9 @@ export function title() {
 
 	return shadow;
 }
+
+export function game() {
+	let shadow = root();
+	
+	return shadow;
+}
diff --git a/js/world/body.mjs b/js/world/body.mjs
new file mode 100644
index 0000000..7679640
--- /dev/null
+++ b/js/world/body.mjs
@@ -0,0 +1,26 @@
+import {GRAVITATIONAL_CONSTANT as G} from '../consts.mjs';
+
+export default class Body {
+	constructor(x, y, mass) {
+		this.x = x;
+		this.y = y;
+		this.r = 0;
+		this.xvel = 0;
+		this.yvel = 0;
+		this.rvel = 0;
+		this.mass = mass;
+	}
+	
+	tickGravity(bodies) {
+		bodies.forEach(b => {
+			let force = b.mass / this.mass / (distanceTo(b) ** 2) * G;
+			let angle = Math.atan2(b.y - this.y, b.x - this.x);
+			this.xvel += Math.cos(angle) * force;
+			this.yvel += Math.sin(angle) * force;
+		});
+	}
+
+	distanceTo(body) {
+		return Math.sqrt(((body.x - this.x) ** 2) + ((body.y - this.y) ** 2));
+	}
+}
diff --git a/js/world/celestial.mjs b/js/world/celestial.mjs
new file mode 100644
index 0000000..57b95ea
--- /dev/null
+++ b/js/world/celestial.mjs
@@ -0,0 +1,10 @@
+import Body from './body.mjs';
+
+export default class Celestial extends Body {
+	constructor(x, y, radius, {
+		density = 1,
+		mass = (radius ** 2) * density
+	}) {
+		super(x, y, mass);
+	}
+}
diff --git a/js/world/index.mjs b/js/world/index.mjs
index d19aabe..15f8f1f 100644
--- a/js/world/index.mjs
+++ b/js/world/index.mjs
@@ -1,3 +1,26 @@
 import * as sector from './sector.mjs';
+import * as spawn from './spawn.mjs';
 
 export {getSectorFromWorld, getContainedSectors} from './sector.mjs';
+
+export const entities = new Set();
+export const celestials = new Set();
+export const ships = new Set();
+
+export let playerShip = null;
+
+export function setPlayerShip(ship) {
+	playerShip = ship;
+}
+
+export function init() {
+	entities.clear();
+	celestials.clear();
+	spawn.player();
+}
+
+export function tick() {
+	celestials.forEach(c => c.tick());
+	entities.forEach(e => e.tick());
+	ships.forEach(s => s.tick());
+}
diff --git a/js/world/module.mjs b/js/world/module.mjs
new file mode 100644
index 0000000..17f1456
--- /dev/null
+++ b/js/world/module.mjs
@@ -0,0 +1,15 @@
+export default class Module {
+	constructor(x, y, {
+		name = 'Unnamed Module',
+		type = 'block',
+		mass = 1,
+		...properties
+	}) {
+		this.x = x;
+		this.y = y;
+		this.name = name;
+		this.type = type;
+		this.mass = mass;
+
+	}
+}
diff --git a/js/world/ship.mjs b/js/world/ship.mjs
new file mode 100644
index 0000000..1f79b4e
--- /dev/null
+++ b/js/world/ship.mjs
@@ -0,0 +1,35 @@
+import Module from './module.mjs';
+import Body from './body.mjs';
+
+export default class Ship extends Body {
+	constructor(x, y) {
+		super(x, y, 0);
+
+		this.com = [0, 0];
+		this.modules = new Set();
+	}
+
+	tick() {
+
+	}
+
+	addModule(x, y, properties, options) {
+		let module = new Module(x, y, {...properties, ...options});
+		this.modules.add(module);
+		this.refreshShape();
+	}
+
+	deleteModule(module) {
+		this.modules.delete(module);
+		this.refreshShape();
+	}
+
+	refreshShape() {
+		let points = [];
+		this.modules.forEach(m => points.push([m.x, m.y, m.mass]));
+		this.mass = points.reduce((a, [,,b]) => a + b, 0);
+		this.com = points.reduce(([ax, ay], b) =>
+			[ax + b.x * b.mass, ay + b.y * b.mass], [0, 0])
+			.map(x => x / this.mass);
+	}
+}
diff --git a/js/world/spawn.mjs b/js/world/spawn.mjs
new file mode 100644
index 0000000..c3a8e34
--- /dev/null
+++ b/js/world/spawn.mjs
@@ -0,0 +1,13 @@
+import Ship from './ship.mjs';
+import Module from './module.mjs';
+import {modules} from '../data.mjs';
+import * as world from './index.mjs';
+
+export function player() {
+	let ship = new Ship(0, 0);
+	ship.addModule(0, 0, modules.capsule.small);
+	ship.addModule(0, 1, modules.fuel.small, { filled: true });
+	ship.addModule(0, 2, modules.thruster.light);
+	world.ships.add(ship);
+	world.setPlayerShip(ship);
+}