Small drops on partially wetting surfaces change shape based on their capillary number (Ca); at low Ca, they have a smooth rounded outline.
At intermediate Ca, the drops form a corner at the back, with the angle increasing from flat to 60 degrees as the velocity rises.
At higher Ca values, the drops develop a cusped tail that creates smaller droplets, referred to as "pearls," and these transformations can be explained by the dynamic contact angle along the contact line.