var Player = Container.expand(function () {
	var self = Container.call(this);
	var playerGraphics = self.createAsset('player', 'Player character', .5, .5);
	self.gravity = 1;
	self.jumpForce = 20;
	self.velocity = 0;
	self.jump = function () {
		this.velocity = -this.jumpForce;
	};
	self.update = function () {
		this.y += this.velocity;
		this.velocity += this.gravity;
		if (this.y > 2732) {
			this.y = 2732;
			this.velocity = 0;
		}
	};
});
var Platform = Container.expand(function () {
	var self = Container.call(this);
	var platformGraphics = self.createAsset('platform', 'Platform', .5, .5);
	self.speed = 5;
	self.move = function () {
		this.y += this.speed;
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	var platforms = [];
	var ground = self.createAsset('ground', 'Ground', 0, 1);
	ground.y = 2732;
	ground.speed = 5;
	ground.move = function () {
		this.y += this.speed;
		if (this.y > 2732) {
			this.y = 0;
		}
	};
	var player = self.addChild(new Player());
	player.x = 2048 / 2;
	player.y = ground.y - player.height;
	for (var i = 0; i < 5; i++) {
		var platform = new Platform();
		platform.x = Math.random() * 2048;
		platform.y = i * (2732 / 5);
		platforms.push(platform);
		self.addChild(platform);
	}
	LK.on('tick', function () {
		player.update();
		ground.move();
		for (var i = 0; i < platforms.length; i++) {
			platforms[i].move();
			if (platforms[i].y > 2732) {
				platforms[i].y = 0;
				platforms[i].x = Math.random() * 2048;
			}
			if (player.intersects(platforms[i]) && player.velocity > 0) {
				player.jump();
			}
		}
	});
	stage.on('down', function (obj) {
		var event = obj.event;
		var pos = event.getLocalPosition(self);
		if (player.intersects(pos)) {
			player.jump();
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -28,8 +28,15 @@
 	var self = Container.call(this);
 	var platforms = [];
 	var ground = self.createAsset('ground', 'Ground', 0, 1);
 	ground.y = 2732;
+	ground.speed = 5;
+	ground.move = function () {
+		this.y += this.speed;
+		if (this.y > 2732) {
+			this.y = 0;
+		}
+	};
 	var player = self.addChild(new Player());
 	player.x = 2048 / 2;
 	player.y = ground.y - player.height;
 	for (var i = 0; i < 5; i++) {
@@ -40,8 +47,9 @@
 		self.addChild(platform);
 	}
 	LK.on('tick', function () {
 		player.update();
+		ground.move();
 		for (var i = 0; i < platforms.length; i++) {
 			platforms[i].move();
 			if (platforms[i].y > 2732) {
 				platforms[i].y = 0;