In simple way, we say that it is due to the surface tension. There are some Facts for understanding the surface tension:
According to the surface tension :
Bubbles (hollow drop) —Surface tension acts to minimize surface (radius of spherical shell of liquid), but opposed by pressure of vapor.
Surface tension enables insects to walk on surface of water —
- High intermolecular forces = greater surface tension
- Cohesion causes water to form drops
- surface tension causes them to be nearly spherical
- adhesion keeps the drops in place
- intermolecular attraction forces act to minimize surface area of liquid
- Geometric shape w/smallest ratio of surface area to volume is sphere
- Surface molecules drawn inward and area of surface of liquid reduced
- :small quantities of liquid form spherical drops
- As drops get larger, weight deforms them into typical tear shape.