  While obtaining theoretical predictions for dissipation during sliding motion
is a difficult task, one regime that allows for analytical results is the
so-called noncontact regime, where a probe is weakly interacting with the
surface over which it moves. Studying this regime for a model crystal, we
extend previously obtained analytical results and confirm them quantitatively
via particle based computer simulations. Accessing the subtle regime of weak
coupling in simulations is possible via use of Green-Kubo relations. The
analysis allows to extract and compare the two paradigmatic mechanisms that
have been found to lead to dissipation: phonon radiation, prevailing even in a
purely elastic solid, and phonon damping, e.g., caused by viscous motion of
crystal atoms. While phonon radiation is dominant at large probe-surface
distances, phonon damping dominates at small distances. Phonon radiation is
furthermore a pairwise additive phenomenon so that the dissipation due to
interaction with different parts (areas) of the surface adds up. This additive
scaling results from a general one-to-one mapping between the mean
probe-surface force and the friction due to phonon radiation, irrespective of
the nature of the underlying pair interaction. In contrast, phonon damping is
strongly nonadditive, and no such general relation exists. We show that for
certain cases, the dissipation can even {\it decrease} with increasing surface
area the probe interacts with. The above properties, which are rooted in the
spatial correlations of surface fluctuations, are expected to have important
consequences when interpreting experimental measurements, as well as scaling
with system size.
