Evolution of particle rms speed in the shearing box for a simulation with normal collisions (KS, blue/black line) and a simulation in which the relative Keplerian shear is subtracted when determining the collision time-scale and outcome (NS, red/gray line). The top panel shows the decay of initially random particle motion due to inelastic collisions (ϵ = 0.3). The rms speed can not fall below v_rms ≈ (δx)Ω for KS collisions, due to the energy release from the Keplerian shear. In the simulation with NS collisions, on the other hand, the rms speed continues to decay towards zero. In the bottom panel we consider elastic collisions (ϵ = 1.0) with zero random motion initially. Energy is released from the Keplerian shear. The blue line shows results of simulations with NS collisions, rerun from snapshots of the KS simulation at various times. The two solutions match increasingly well when the particle rms speed increases above (δx)Ω.