title: Set a physicsbody to a constant velocity
body: <h2>Moving a ball with constant velocity</h2>
  
  <p>I tried to make a box of balls where the balls move with constant velocity. The shouldn't slow down when they collide with each other. I think I have set all properties right but it didn't work and after 30s all of the balls stopped to move.</p>
  
  <p>The box is set like this:</p>
  
  <pre><code>    self.physicsBody = SKPhysicsBody(edgeLoopFromRect: self.frame)
      self.physicsBody.dynamic = false
      self.physicsBody.restitution = 1
      self.physicsBody.friction = 0
  </code></pre>
  
  <p>The balls are set like this: </p>
  
  <p><img src="https://i.stack.imgur.com/7Hfnd.png" alt="enter image description here"></p>
  
  <p>Is this a bug of the physics engine or am I missing something?</p>