title: Pong physics problem
body: <p>I have problem but I don't know how to describe it so I have drawn it.</p>
  
  <p><img src="https://i.stack.imgur.com/LY2q7.jpg" alt="Pong Physics Graphic"></p>
  
  <p>As you can see ball bounces when collision is detected. Nevermind the angle - I have just drawn it that way.
  But sometimes ball goes through the paddle leaving it other way.</p>
  
  <p>Why that happens ? Becase when I detect the collision I change vx to -vx. What should I do in that case ? Change also y ? But how to check which side of the paddle ball hit?</p>
  
  <p>Maybe other ideas?</p>