# Approach to equilibrium: Two partitions

## Introduction

This program is similar to the molecular dynamics of a gas initially confined to the center of three partitions. In this simulation the particles are initially confined to the left half of the box. Because of the use of periodic boundary conditions, the visualization of the trajectories of the particles might be confusing because it looks like some particles are moving into the right half of the box from two directions.

See: [Introduction to STP] and [Approach to Equilibrium]

## Problems

1. Run the simulation with the default initial values. How long does it take before the system appears to be in equilibrium? What is your criterion for equilibrium?
2. Explain the use of periodic boundary conditions.
3. *Run the system with N = 270 until t = 5. Then press the Reverse button, which reverses all the velocities, and continue the simulation. Does the system return to its initial state? Repeat for other times. Is there a time at which the system does not return to its initial state? Repeat for N = 27. What can you conclude about the N dependence of reversibility?

Updated 20 March 2020.