title: How to pin one SKPhysicBody to another without both falling
body: <p>I am trying to join two SKPhysicsBodies together so that the one on top stays in place and the one below falls with gravity but is attached with a joint.  Imagine two rectangles, one on top and one below.  The one on top stays in place "floating" and the one below is attached with a joint and can move (swing perhaps or bounce etc)</p>
  
  <p>When I attempt to create this, both nodes fall with gravity even if I set the affectedByGravity to NO.</p>
  
  <pre><code>self.backgroundColor = [SKColor colorWithRed:0.15 green:0.15 blue:0.3 alpha:1.0];
  
      self.physicsWorld.gravity = CGVectorMake(0, -9.8);
  
  
      SKLabelNode *myLabel = [SKLabelNode labelNodeWithFontNamed:@"myFont"];
  
      myLabel.text = @"Hello, World!";
      myLabel.fontSize = 30;
      myLabel.position = CGPointMake(CGRectGetMidX(self.frame),
                                     CGRectGetMidY(self.frame));
  
      myLabel.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:myLabel.frame.size];
      myLabel.physicsBody.affectedByGravity = NO;
  
       [self addChild:myLabel];
  
  
  
      SKLabelNode *myLabel2 = [SKLabelNode labelNodeWithFontNamed:@"myFont"];
  
      myLabel2.text = @"Hello, World!";
      myLabel2.fontSize = 30;
      myLabel2.position = CGPointMake(CGRectGetMidX(self.frame),
                                     CGRectGetMidY(self.frame));
  
      myLabel2.physicsBody = [SKPhysicsBody bodyWithRectangleOfSize:myLabel2.frame.size];
  
  
      [self addChild:myLabel2];
  
  
      CGPoint anchor = CGPointMake(CGRectGetMidX(self.frame),
                                   CGRectGetMidY(self.frame));
      SKPhysicsJointFixed* fixedJoint = [SKPhysicsJointFixed jointWithBodyA:myLabel.physicsBody
                                                                      bodyB:myLabel2.physicsBody
                                                                     anchor:anchor];
      [self.scene.physicsWorld addJoint:fixedJoint];
  </code></pre>