  We study a model inspired by the pinball machine involving chaotic scattering
of particles on hard disks with inelasticity. This system exhibits sensitivity
not only on the initial conditions of the scattering point particle but also on
the external force produced by the pinballs. The deflection function shows
fractal structure with regions of wild oscillations which are exponentially
compressed as a function of the force exerted by the hard disks. The chaotic
properties of the repeller, such as the scaling of the fractal dimension, the
Lyapunov exponents and the pressure function, are studied for different
geometric configurations.
