Question

The spherical shape of rain drops is due to?
a. Atmospheric friction of air
b. Gravity of spherical earth
c. The surface tension of rainwater
d. Viscosity of rainwater

Answer 1

Hint: Any cluster of atoms that has the freedom to move in space eventually becomes spherical, be it water droplets, planets, or even gigantic stars. A sphere has the least surface area which is why it can be deemed as the most stable shape.

Complete answer: Raindrops, even when they could've been of any shape, are spherical. This shape is the outcome of a competition between two forces specifically: the surface tension of the water droplet and pressure of the air pushing it from all sides (atmospheric pressure). In this competition, the surface tension emerges out to be more dominant. The smaller a raindrop, the more spherical it is as the air molecules have a smaller area to attack the water ball, which leads to lesser distortion. This feat of nature isn't just restricted to water drops. The spherical shape seems to be an extremely preferred shape by nature, and this is no coincidence! The sphere is the most symmetrical shape of all. And thus has the least surface area which is why it can be deemed as the most stable shape to exist in nature. Therefore it is not surprising that we see so many spherical objects in nature.
Thus the spherical shape allows raindrops to resist external forces (primarily air drag) with the most efficient and thus maintain their shape.
Looking at the options given:
Option a- Atmospheric friction of air cannot be the right answer since it would disrupt the shape of the water droplets because of resistance.
Option b- Gravity of spherical Earth has little role to play in the shape of the water droplets. The role is limited to drops falling on earth due to gravity but is limited to that.
Option c- Surface tension is the right answer because the smaller a raindrop, the more spherical it is as the air molecules have a smaller area to attack the water ball, which leads to lesser distortion.
Option d- Viscosity of rainwater is defined by how thick the fluid is. Therefore this cannot be the right answer.

Option “c” is the correct answer.

Note: Rain is the most essential component of the water cycle. It is responsible for depositing most of the freshwater on planet Earth. It is the main source of irrigation in many parts of India even today.