Align -- makes the molecules want to align with the displacement,
of the mouse from center of region, strength proportional to displacement
Curl -- a: twists the molecules. b: applies a force proportional to r cross zhat ( r= displacement of molecule from center of region )
Twist -- just applies a torque ( proportional to y component of mouse
displacement) to re-orient the molecules
Brush -- the "Brush your thumb across" force: force proportional to displacement of mouse when button released, velocity proportional to same*
Fixed -- applies a force on the molecules proportional to mouse
displacement
Viscous -- applies a force proportional to mouse displacement at mouse up,
the region moves with the average velecity of the molecules contained*
* persitent forces last until: the region moves outside the box,
or the mouse is pressed again.