  We describe an experiment in which cold rubidium atoms, confined in an
elongated magnetic trap, are excited by transverse oscillation of the trap
centre. The temperature after excitation exhibits resonance as a function of
the driving frequency. We measure these resonances at several different trap
frequencies. In order to interpret the experiments, we develop a simple model
that incorporates both collisions between atoms and the anharmonicity of the
real three-dimensional trapping potential. As well as providing a precise
connection between the transverse harmonic oscillation frequency and the
temperature resonance frequency, this model gives insight into the heating and
loss mechanisms, and into the dynamics of driven clouds of cold trapped atoms.
