diff --git a/docs/content/articles/van.md b/docs/content/articles/van.md
index e82ea47..9f2ae73 100644
--- a/docs/content/articles/van.md
+++ b/docs/content/articles/van.md
@@ -38,6 +38,8 @@ For simplicity, let's make them rectangles.
 
 ### Movement
 
+Each tick of the game loop simulates some elapsed time. Pong is a world of elastic collisions. The only thing that needs to be tracked is position and direction.
+
 #### Ball
 
 Ball movement is simple, the ball has a constant velocity and an angle.