  In this note we present complete, closed-form expressions for random relative
velocities between colliding particles of arbitrary size in nebula turbulence.
These results are exact for very small particles (those with stopping times
much shorter than the large eddy overturn time) and are also surprisingly
accurate in complete generality (that is, also apply for particles with
stopping times comparable to, or much longer than, the large eddy overturn
time). We note that some previous studies may have adopted previous simple
expressions, which we find to be in error regarding the size dependence in the
large particle regime.
