In order to find out what the forces on the plasma in a radial plasma source (RPS) are, detailed measurements of radial profiles of the plasma variables, employing Langmuir and emissive probes, were performed, for various gas flow rates. The measured plasma variables were the plasma density, the electron temperature and the plasma potential. The profiles were used for estimating the plasma pressure and the electric force on the ions. The estimated electric force was found to be approximately equal to the measured force exerted by the flow outward of the RPS on a balance force meter, as it should be, and to be considerably larger than the force due to the plasma pressure. It was concluded therefore that the magnetic pressure is likely to be the dominant force on the plasma. In addition, most of the potential drop (and maximal radial electric field) were found to be located where the axial magnetic field is large, as expected in a crossed electric and magnetic field acceleration by magnetic pressure.