This is a shot from a three dimensional computer simulation of the process of en:osmosis. The blue en:mesh is impermeable to the larger balls, whereas all of the balls are (in the animated version) bouncing about according to the rules of physical simulation of the kinetics of an ideal gas. Averaged over long period of time, each ball has has the same kinetic energy as each of the other balls, even though at any given moment the velocities are distributed according to the appropriate en:Boltzmann functions. Likewise, each species (in this case color) of balls (as a group) exerts time averaged force (due to the bouncing) upon the walls of the box, which corresponds to the partial en:pressure contribution associated with that group. These properties emerge even though the collision function used in the simulation is trivial, to wit:

void Mass::collide (Mass *X)
{
  vector v_cm;
  v_cm = (velocity*mass+X->velocity*X->mass)/(mass+X->mass);
  velocity = v_cm*2 - velocity;
  X->velocity = v_cm*2 - X->velocity;
  m_bCollision = true;
  X->m_bCollision = true;
}