This Demonstration models the collision of two liquid droplets that merge into a single drop after collision without splashing. This is the ultimate case of an inelastic collision. The dynamics are determined by momentum conservation: the vector sum of the momenta of the two colliding droplets equals the momentum of the resulting droplet. You can vary the masses and initial speeds of the droplets. With the time slider, you can observe the collision in slow motion in either the laboratory or the center of mass frame of reference.