Question

why Porter place a thick round piece of clothes on their head

Answer 1

hey mate...
pressure is inversely proportional to area....
the cloth on the porters head increases the surface area and thus decreases the pressure on his head.

hope it helps

Answer 2

A headgear like the one you mentioned, which is the potter’s cap, helps to distribute the weight of the heavy pots evenly over the carrier’s head. They use a thick piece of cloth to absorb the shock they suffer while walking long distances so that the pot remains static over the head.