Ask Uncle Pai — Why do whales come to the surface?

The spider constructs its web with the silk threads given out from a group of spinnerets on its underside, near the tip of its abdomen. First, the spider builds a sort of scaffolding or framework of non-sticky thread. Then it lays down the closely knit spiral of silky threads, distinguished by beads along each thread. It is on these sticky threads that the prey gets trapped. The spider, however, knows its own web and with its fine sense of touch, uses the non-sticky threads to move along its web. Hence it does not get caught.

Q When a little petrol spills over and falls on the ground why does it look multi-coloured?

The colours are seen when there is a little moisture or water where the petrol has fallen. This happens because of the phenomenon called refraction or bending of light when it passes from one medium to another. White light is composed of violet, indigo, blue, green, yellow, orange and red and each of these colours bend at a slightly different angle than the other. Hence the multi-colour effect.

Q Why do whales come to the surface every now and then?

— Poonam M Ahuja, Bandra

Fish take in oxygen dissolved in water with the help of their gills. Whales do not have such a mechanism in their body. They are actually mammals, who shifted from land to sea, millions of years ago.

They have to breathe in oxygen from the air for survival. So every now and then they come up to the surface of the water to breathe in oxygen.

Q Why do puris bulge when fried?

— Chaitanya N Korgaonkar, Raigad

Puris bulge when moisture in the dough turns into steam in the frying pan and tries to escape.