The Nucleus solver attributes control the internal forces that affect all of the Nucleus objects that are members of the same solver system. 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. Depending on the scale of the character model to which you assign nHair, you may need to adjust the Nucleus Space Scale attribute so that solver applies real world gravity to the simulation.
When you reduce the Space Scale value, Maya evaluates the objects in the simulation as if they were much smaller in size. This results in a visibly increased gravitational effect on the hair curves.
In the next section of the lesson, you render a single frame of your nHair simulation.