title: Pygame, simple physics engine, how to hold points between planes?
body: <p>I'm trying to write <a href="http://www.wildbunny.co.uk/blog/2011/04/06/physics-engines-for-dummies/" rel="nofollow">this</a> tutorial in Pygame(Python) and having problems about holding points between planes.</p>
  
  <p>My code is: <a href="https://github.com/osa1/pygame-playground/raw/master/fiz2.py" rel="nofollow">fiz2.py</a></p>
  
  <p>Vector class: <a href="https://github.com/osa1/pygame-playground/raw/master/vector.py" rel="nofollow">vector.py</a></p>
  
  <p>If you move mouse on the Pygame screen, the planes will rotate. And when the planes are rotating, points are passing through planes and going outside.</p>
  
  <p>I tried to fix points' positions on every iteration but they still passed the planes. I have no idea about where should I fix their positions.</p>
  
  <p>NOTE: I know my code is a little bit messy, this is my first 2d program and I had really hard times getting used to Pygame's coordinate plane and vectors. I will re-write when I solve this.</p>
  
  <p>NOTE2: Yes, I wrote the comment about how to hold points between planes on the tutorial, I understand the way he fixes positions but have no idea about how(and where, in code) to implement it.</p>
  
  <p>Thanks.</p>