ha sprezzo made me look 
dx, dy are vector components sped up or slowed down by so called mass, just a scalar multiplier.
Code: (Select All)
TYPE PARTICLE ' PARTICLE PROPERTIES
x AS SINGLE ' y location
y AS SINGLE ' x location
'xv AS SINGLE ' y vector ????
dx as single ' the change over the x-axis of particle position
'yv AS SINGLE ' x vector ????
dy as single ' the change over the y-axis of the particle position
END TYPE
b = b + ...