no. velocity is a vector of speeds [x,y,z]
x = east/west speed
y = north/south speed
z = vertical speed
so setvelocity [1,1,1] would give them a velocity of 1 (m/s? km/hr? some measurement i'll go with km/hr) west,1 km/hr north, and one km/hr up
so to stop them from being held you would just use a condition to exit the loop holding there velocity at [0,0,0]