Ehrenfest's model (simple)

Author:
Denis
In the beginning N identical particles (or balls) randomly are disrtibuted over M containers (or urns). Every step we select one ball with equal probability and move it to another (also random) urn. With "Explanation" mode all the process is depicted slowly. If N is high it's good to choose "BarChart" display method.
1. What is going on with initial distribution? 2. What is equilibrium distribution? 3. How relative fluctuations depend on N?