KnowHOW team explains: Water drops, or, for that matter, the drops of any other liquid, are spherical in shape due to a phenomenon called surface tension. In a liquid this acts on the surface of a freely falling drop to minimise its area.

Compared to other objects, such as an ellipsoid (an egg-shaped object), the ratio between the surface area and the volume is minimum in case of a sphere.

Surface tension, in simpler terms, is the tendency of the surface of a liquid to behave like a stretched membrane. This results from the attraction between the molecules in the liquid.

Molecules at the surface of any liquid, unlike the ones in the interior, do not experience a uniform attractive force. The ones at the intersurface of liquid and air are attracted more towards the bulk of the liquid. As a consequence, all liquid surfaces, in the absence of any other external force, tend to contract. Since a sphere has got the minimum surface-to-volume ratio, falling liquid drops are always spherical in shape.

In the case of bubbles also, it is surface tension that plays a major role in determining their shape.

The question was sent by Falguni Chattopadhyay from Calcutta-9