Drop, a small volume of liquid which in equilibrium is bounded by a surface of revolution. Drops form when a liquid flows slowly out of a small opening or runs off the edge of a surface, when a liquid is atomised or emulsified, and also when vapour condenses on solid non-wettable surfaces or, in a gaseous medium, on condensation centres.
The shape of a drop is determined by surface tension and by external forces (for example gravity). Microscopic drops, for which gravity does not play a large part, and drops in weightless conditions have the shape of a sphere. Large drops in terrestrial conditions have the shape of a sphere only when the density of the drop and that of the surrounding medium are equal. Falling raindrops are flattened on one side by gravity, by the pressure of the oncoming stream of air and by surface tension. On wettable surfaces drops spread out; on non-wettable ones they take the shape of a flattened sphere (see Wetting). The shape and size of the drops flowing out of a capillary tube depend on its diameter, on the surface tension σ and on the density of the liquid, which makes it possible to determine σ from the weight of the drops.
The shape of a drop is determined by surface tension and by external forces (for example gravity). Microscopic drops, for which gravity does not play a large part, and drops in weightless conditions have the shape of a sphere. Large drops in terrestrial conditions have the shape of a sphere only when the density of the drop and that of the surrounding medium are equal. Falling raindrops are flattened on one side by gravity, by the pressure of the oncoming stream of air and by surface tension. On wettable surfaces drops spread out; on non-wettable ones they take the shape of a flattened sphere (see Wetting). The shape and size of the drops flowing out of a capillary tube depend on its diameter, on the surface tension σ and on the density of the liquid, which makes it possible to determine σ from the weight of the drops.