What force keeps a droplet together?

The force that keeps a droplet together is best described as static surface tension. Static surface tension arises from the cohesive forces between liquid molecules at the surface of a droplet. These molecules are pulled together due to intermolecular attractions, creating a minimized surface area and maintaining the integrity of the droplet.

When a liquid is at rest, static surface tension is what allows droplets to form typical shapes, such as spheres, due to the balance of forces at the surface. Dynamic surface tension pertains to the changing tension of a liquid surface during motion or when a droplet is forming or breaking apart. This concept is more applicable to scenarios where liquid is actively spreading or flowing, rather than maintaining the cohesive structure of a droplet at rest.

Capillary action involves the movement of liquid within narrow spaces and is a result of adhesive forces between the liquid and surface material, which is not directly responsible for holding a droplet together in its stable form. Adhesive force concerns the attraction between different substances, such as liquid and solid, rather than the cohesive forces that keep a droplet intact.

Understanding these different types of forces is crucial for aerial applicators who need to know how droplets behave during application to ensure even distribution and effective coverage of pesticides or fertilizers.