With this function you can find out what the current density is for particles in the physics simulation (you can set this value using physics_particle_set_density()).
physics_particle_get_damping()
if (physics_particle_get_density() < 1)
{
physics_particle_set_density(physics_particle_get_density() + 0.01);
}
The above code will check the current density value for all particles in the system and if it is less than 1 then it will add 0.01 to it.