Abstract
Using a shaking field overlaped to the static field of a quadrupole trap we have performed experiments with cold Na atoms held in a magnetic trap. As a function of the shaking frequency the temperature of the atomic cloud is measured by time-of-flight. We observe results similar to Kumakura et al. [Phys. Rev. A 68, 021401(R)] and the variations of the kinetic temperature in our results are explained based on a model where we selectively affect different velocity classes.