  We study the effect of shear on the aging dynamics of a colloidal suspension
of synthetic clay particles. We find that a shear of amplitude $\gamma$ reduces
the relaxation time measured just after the cessation of shear by a factor
$\exp(-\gamma/\gamma_c)$, with $\gamma_c \sim 5%$, and is independent of the
duration and the frequency of the shear. This simple law for the rejuvenation
effect shows that the energy involved in colloidal rearrangements is
proportional to the shear amplitude, $\gamma$, rather than $\gamma^2$, leading
to an Eyring-like description of the dynamics of our system.
