Adjusting the Nucleus solver properties is an important step of creating an nParticle effect. The Nucleus solver properties control internal forces that affect all of the nodes that are members of a solver system. One of the most significant Nucleus solver attributes is Space Scale.
The Nucleus solver applies Gravity and Wind forces to objects as if the objects were scaled in meters, regardless of the units in which your scene was created. To maintain the effect of real world gravity, you need to adjust the Nucleus Space Scale to suit your simulation.