frztrb,
try something like this in law:
FormalLength.1=sin(50*2*PI*FormalReal.1 /10*1 rad)*50 mm
FormalLength.1-Y coordinates of Sinus Function in fog law (type of Length)
FormalReal.1 - parameter t with values [0,1] varied on required length, 1000mm for example (type of Real)
Playing with...