var Boot = Container.expand(function () {
	var self = Container.call(this);
	var bootGraphics = self.createAsset('boot', 'Boot', .5, .5);
	self.velocityX = 0;
	self.velocityY = 0;
	self.previousX = 0;
	self.previousY = 0;
	self.calculateVelocity = function () {
		self.velocityX = self.x - self.previousX;
		self.velocityY = self.y - self.previousY;
		self.previousX = self.x;
		self.previousY = self.y;
	};
});
var Ball = Container.expand(function () {
	var self = Container.call(this);
	var ballGraphics = self.createAsset('ball', 'Soccer Ball', .5, .5);
	self.velocityY = 0;
	self.gravity = 0.5;
	self.bounceFactor = 0.7;
	self.move = function () {
		self.x += self.velocityX;
		self.y += self.velocityY;
		self.velocityY += self.gravity;
		if (self.y > 2732 - self.height / 2) {
			self.velocityY *= -self.bounceFactor;
			self.y = 2732 - self.height / 2;
		}
		if (self.x < 0 || self.x > 2048) {
			self.velocityX *= -1;
		}
	};
	self.bounce = function (boot) {
		var dx = self.x - boot.x;
		var dy = self.y - boot.y;
		var distance = Math.sqrt(dx * dx + dy * dy);
		if (distance < boot.width / 2 + self.width / 2) {
			var normalX = dx / distance;
			var normalY = dy / distance;
			var dotProduct = normalX * boot.velocityX + normalY * boot.velocityY;
			self.velocityX = -2 * dotProduct * normalX + boot.velocityX;
			self.velocityY = -2 * dotProduct * normalY + boot.velocityY;
		}
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	stage.on('move', function (obj) {
		var pos = obj.event.getLocalPosition(self);
		boot.x = pos.x;
		boot.y = pos.y;
		boot.calculateVelocity();
	});
	var ball = self.addChild(new Ball());
	ball.x = 2048 / 2;
	ball.y = 2732 / 2;
	var boot = self.addChild(new Boot());
	boot.visible = true;
	var scoreTxt = new Text2('0', {
		size: 150,
		fill: "#ffffff"
	});
	scoreTxt.anchor.set(.5, 0);
	LK.gui.topCenter.addChild(scoreTxt);
	var isGameOver = false;
	var isGameStarted = false;
	stage.on('down', function (obj) {
		var pos = obj.event.getLocalPosition(self);
		boot.x = pos.x;
		boot.y = pos.y;
		boot.visible = true;
		if (!isGameStarted) {
			ball.bounce(boot);
			isGameStarted = true;
		}
	});
	LK.on('tick', function () {
		if (isGameStarted) {
			ball.move();
			var dx = boot.x - ball.x;
			var dy = boot.y - ball.y;
			var distance = Math.sqrt(dx * dx + dy * dy);
			if (distance < boot.width / 2 + ball.width / 2) {
				ball.bounce(boot);
			}
		}
		if (ball.y > 2732 - ball.height / 2) {
			isGameOver = true;
		}
		if (isGameOver) {
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -5,10 +5,10 @@
 	self.velocityY = 0;
 	self.previousX = 0;
 	self.previousY = 0;
 	self.calculateVelocity = function () {
-		self.velocityX = self.previousX - self.x;
-		self.velocityY = self.previousY - self.y;
+		self.velocityX = self.x - self.previousX;
+		self.velocityY = self.y - self.previousY;
 		self.previousX = self.x;
 		self.previousY = self.y;
 	};
 });
@@ -33,13 +33,15 @@
 	self.bounce = function (boot) {
 		var dx = self.x - boot.x;
 		var dy = self.y - boot.y;
 		var distance = Math.sqrt(dx * dx + dy * dy);
-		var normalX = dx / distance;
-		var normalY = dy / distance;
-		var dotProduct = normalX * boot.velocityX + normalY * boot.velocityY;
-		self.velocityX = -2 * dotProduct * normalX + boot.velocityX;
-		self.velocityY = -2 * dotProduct * normalY + boot.velocityY;
+		if (distance < boot.width / 2 + self.width / 2) {
+			var normalX = dx / distance;
+			var normalY = dy / distance;
+			var dotProduct = normalX * boot.velocityX + normalY * boot.velocityY;
+			self.velocityX = -2 * dotProduct * normalX + boot.velocityX;
+			self.velocityY = -2 * dotProduct * normalY + boot.velocityY;
+		}
 	};
 });
 var Game = Container.expand(function () {
 	var self = Container.call(this);