title: Setting up a Ground node using SpriteKit?
body: <p>I've been designing a game where I want the game to stop as soon as the ball makes contact with the ground. My function below is intended to set up the ground.</p>
  
  <pre><code>class GameScene: SKScene, SKPhysicsContactDelegate {
  
       var ground = SKNode() 
  
       let groundCategory: UInt32 = 0x1 &lt;&lt; 0
       let ballCategory: UInt32 = 0x1 &lt;&lt; 1
  
       //Generic Anchor coordinate points
       let anchorX: CGFloat = 0.5
       let anchorY: CGFloat = 0.5
       /*Sets the background and ball to be in the correct dimensions*/
  
       override init(size: CGSize) {
           super.init(size: size)
  
           //Create the Phyiscs of the game
           setUpPhysics()  
  
           setUpGround()   
  
           setUpBall()
      }
  
      func setUpPhysics() -&gt; Void {
          self.physicsWorld.gravity = CGVectorMake( 0.0, -5.0 )
          self.physicsWorld.contactDelegate = self
      }
  
       func setUpGround() -&gt; Void {
          self.ground.position = CGPointMake(0, self.frame.size.height)
          self.ground.physicsBody = SKPhysicsBody(rectangleOfSize: CGSizeMake(self.frame.size.width, self.frame.size.height)) //Experiment with this
          self.ground.physicsBody?.dynamic = false
  
          self.ground.physicsBody?.categoryBitMask = groundCategory    //Assigns the bit mask category for ground
          self.ball.physicsBody?.contactTestBitMask = ballCategory  //Assigns the contacts that we care about for the ground
  
          /*Added in*/
          self.ground.physicsBody?.dynamic = true
  
          self.ground.physicsBody?.affectedByGravity = false
          self.ground.physicsBody?.allowsRotation = false
          /**/
  
          self.addChild(self.ground)
      }
  
      func setUpBall() -&gt; Void {
  
          ball.anchorPoint = CGPointMake(anchorX, anchorY)
  
          self.ball.position = CGPointMake(self.frame.size.width/2, self.frame.size.height/2)
  
          self.ball.name = "ball"
          self.ball.userInteractionEnabled = false
  
          ball.physicsBody?.usesPreciseCollisionDetection = true
  
          self.ball.physicsBody?.categoryBitMask = ballCategory    //Assigns the bit mask category for ball
          self.ball.physicsBody?.collisionBitMask = wallCategory | ceilingCategory //Assigns the collisions that the ball can have
          self.ball.physicsBody?.contactTestBitMask = groundCategory   //Assigns the contacts that we care about for the ball
  
          addChild(self.ball)  //Add ball to the display list
      }
  </code></pre>
  
  <p>The problem I am noticing is that when I run the iOS Simulator, the Ground node is not being detected. What am I doing wrong in this case?</p>