A = (0, 1)
B = (3, 1)
u = Vector(A, B)
a = 2 (slider from -5 to 5, step 0.1)
b = 3
r2: u * u
k = 1 (slider from -5 to 9.0E9, step 0.1)
f: k * a * b / r2
fFattoreScala = 0.5
fRpr: f / fFattoreScala