A droplet is a relatively small amount of liquid, which is constrained by a surface. This surface is determined primarily by the surface tension forces. The droplet shape is specified by the surface tension force, as well as by the gravity and aerodynamic forces. Under normal conditions, the surface tension force is dominant for the droplets of small size (up to 1 mm). Smaller droplets have a shape closer to a sphere. The effect of gravity force becomes more significant, as the droplet size increases. As a consequence, the droplet velocity and aerodynamic forces increase. Such droplets deform and take on flattened shape.
Shape and size of the droplet that separates from a capillary tip depend on the capillary diameter, surface tension, and liquid density. This dependence creates a basis for the methods for specification of the liquid surface tension using the amount of droplets that separate from a vertical cylindrical tube and by the shape of a droplet hanging at the tip of the tube.