  We derive a semiclassical equation of motion for a `composite' quark in
strongly-coupled large-N_c N=4 super-Yang-Mills, making use of the AdS/CFT
correspondence. The resulting non-linear equation incorporates radiation
damping, and reduces to the standard Lorentz-Dirac equation for external forces
that are small on the scale of the quark Compton wavelength, but has no
self-accelerating or pre-accelerating solutions. From this equation one can
read off a non-standard dispersion relation for the quark, as well as a Lorentz
covariant formula for its radiation rate.
