Physics issue: ball is bouncing too high - swift

Question

I am working on game where a ball bounces and hits a platform and then bounces right back. Ideally the ball should bounce to exactly the height that it started at. However, in my game the ball slowly keeps bouncing higher and higher. I've looked at the documentation and tried to change all of the physics properties but nothing seems to work.
Any suggestions?
import SpriteKit
class GameScene: SKScene, SKPhysicsContactDelegate {
let ballCategory:UInt32 = 0x1 << 0;
let circleCategory:UInt32 = 0x1 << 1;
let platformCategory:UInt32 = 0x1 << 2;
var ball = SKShapeNode(circleOfRadius: 20.0)
var circle = SKShapeNode(circleOfRadius: 200.0)
var platform = SKShapeNode(rectOfSize: CGSizeMake(10, 1))
var circleColor = 2
var ballColor = 3
var scoreLabel: SKLabelNode!
var score = 0
override func didMoveToView(view: SKView) {
setUpLabels()
self.physicsWorld.contactDelegate = self
backgroundColor = (UIColor.whiteColor())
ball.fillColor = SKColor.redColor()
ball.strokeColor = SKColor.clearColor()
ball.position = CGPoint(x: self.size.width/2, y: self.size.height/2+60)
ball.physicsBody = SKPhysicsBody(circleOfRadius: 20)
ball.physicsBody?.categoryBitMask = ballCategory
ball.physicsBody?.collisionBitMask = platformCategory
ball.physicsBody?.contactTestBitMask = platformCategory
ball.physicsBody?.dynamic = true
ball.physicsBody?.restitution = 1.0
ball.physicsBody?.affectedByGravity = true
ball.physicsBody?.linearDamping = 0.0
ball.physicsBody?.friction = 0.0
self.addChild(ball)
circle.fillColor = SKColor.clearColor()
circle.strokeColor = SKColor.redColor()
circle.lineWidth = 5.0
circle.position = CGPoint(x: self.size.width/2, y: self.size.height/2)
circle.physicsBody = SKPhysicsBody(edgeLoopFromPath: circle.path)
circle.physicsBody?.categoryBitMask = circleCategory
self.addChild(circle)
platform.fillColor = SKColor.clearColor()
platform.strokeColor = SKColor.clearColor()
platform.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(10, 1))
platform.position = CGPoint(x: self.size.width/2, y: circle.position.y/2)
platform.physicsBody?.categoryBitMask = platformCategory
platform.physicsBody?.dynamic = false
platform.physicsBody?.friction = 0.0
self.addChild(platform)
}
override func touchesBegan(touches: Set<NSObject>, withEvent event: UIEvent) {
circleColor += 1
if circleColor%3 == 1 {
circle.strokeColor = UIColor.redColor()
}
if circleColor%3 == 2 {
circle.strokeColor = UIColor.greenColor()
}
if circleColor%3 == 3 {
circle.strokeColor = UIColor.yellowColor()
}
if circleColor%3 == 4 {
circle.strokeColor = UIColor.greenColor()
}
if circleColor%3 == 5 {
circle.strokeColor = UIColor.blueColor()
}
if circleColor%3 == 0 {
circle.strokeColor = UIColor.yellowColor()
}
}
func didBeginContact(contact: SKPhysicsContact) {
if ball.fillColor == circle.strokeColor {
score += 1
scoreLabel.text = String("Score \(score)")
}
if ball.fillColor != circle.strokeColor {
let transition = SKTransition.revealWithDirection(SKTransitionDirection.Down, duration: 1.0)
let scene = SecondScene(size: self.scene!.size)
scene.scaleMode = SKSceneScaleMode.AspectFill
self.scene!.view!.presentScene(scene, transition: transition)
}
ballColor = Int(arc4random_uniform(10))
if ballColor%3 == 1 {
ball.fillColor = UIColor.redColor()
}
if ballColor%3 == 2 {
ball.fillColor = UIColor.greenColor()
}
if ballColor%3 == 3 {
ball.fillColor = UIColor.yellowColor()
}
if ballColor%3 == 4 {
ball.fillColor = UIColor.greenColor()
}
if ballColor%3 == 5 {
ball.fillColor = UIColor.blueColor()
}
if ballColor%3 == 0 {
ball.fillColor = UIColor.yellowColor()
}
}
func setUpLabels () {
scoreLabel = SKLabelNode(fontNamed: "Arial")
scoreLabel.position = CGPoint(x: 60, y: self.size.height-30)
scoreLabel.text = String("Score \(score)")
scoreLabel.fontColor = UIColor.blackColor()
scoreLabel.fontSize = 25
self.addChild(scoreLabel)
}
override func update(currentTime: CFTimeInterval) {
}
}

Answer 1

Reduce restitution a little which take control of the bounciness of the physics body. Like this:
ball.physicsBody?.restitution = 0.9

Answer 2

In general numerical differential equation solvers that solve the ode for the next time step will introduce energy into the system, which is why you are seeing what you are seeing. You can mitigate this by introduce a damping force. In the case of SpriteKit this means changing the restitution or linear damping factors.
For more about the drift that occurs see: https://en.wikipedia.org/wiki/Energy_drift or http://www.cs.cmu.edu/~baraff/sigcourse/notesb.pdf.