Turpentine oil is flowing through a tube of length `L` and radius `r`. The pressure difference between the two ends of the tube is `p` , the viscosity of the coil is given by `eta = (p (r^(2) - x^(2)))/(4 vL)`, where `v` is the velocity of oil at a distance `x` from the axis of the tube. From this relation, the dimensions of viscosity `eta` are