Water forms droplets on a surface due to a property called surface tension. Surface tension is the tendency of the surface of a liquid to behave like a stretched membrane. It is caused by the cohesive forces between the water molecules. These forces are the attractive forces between molecules of the same kind.
When water is placed on a surface, the water molecules on the surface are not surrounded by other water molecules on all sides. This means that the cohesive forces between these water molecules are stronger than the adhesive forces between the water molecules and the surface. As a result, the water molecules are pulled together, forming a droplet.
The shape of the droplet is determined by the balance of the surface tension forces and the gravitational forces. The surface tension forces tend to make the droplet as small as possible, while the gravitational forces tend to make the droplet spread out. The equilibrium shape is a sphere, which is the shape with the smallest surface area for a given volume.
In the case of a water droplet on a leaf, the surface tension forces are even stronger because the leaf is made of a material that is not wet by water. This means that the adhesive forces between the water molecules and the leaf are very weak. As a result, the water droplets form very small, nearly spherical droplets.
Here are some other factors that can affect the shape of water droplets:
- The temperature of the water: The surface tension of water decreases as the temperature increases. This means that water droplets will be less spherical at higher temperatures.
- The roughness of the surface: The rougher the surface, the more likely it is that the water droplets will spread out.
- The presence of impurities: Impurities in the water can disrupt the surface tension, causing the water droplets to spread out.