In many devices a relationship between viscosity and ion heat transport has been observed. This coupling can be attributed to turbulence, which is also a common feature in fluid dynamics. For plasmas, ITG turbulence theory predicts a one-to-one relationship, which is furthermore assumed in many plasma models. In this work, a detailed study on momentum and heat transport has been carried out. The research focussed on the determination of the Prandtl number, Pr cf/ci, which describes the coupling between momentum and heat transport. A better understanding of plasma rotation and momentum transport is of importance for the development of low torque ITER scenarios. An experimental study on plasma rotation has been carried out on predominantly Neutral Beam (NBI) heated JET discharges. The JET neutral beams are injected at 2 different octants, each injecting 8 independent neutral beams. Each beam has a tangential component and thus applies a torque to the plasma. For standard operations, NBI is in co-current direction. Charge Exchange Recombination Spectroscopy (CXRS) is used to measure the toroidal rotation velocity and ion temperature profiles. The JET CXRS diagnostic determines the profiles at 9 radial locations. The measured quantities are those of Carbon ions. In this study, it is assumed that the deuterium ions have the same temperature and velocities as the carbon ions. Especially for plasmas with large pressure gradients, such as those with an Internal Transport Barrier (ITB), this assumption does not necessarily hold and the rotation profiles need to be corrected.