Question

the cover of a ball point pen has a small hole.explain it's function

Answer 1

Answer:

to let the liquid(ink) flow through the ball to help to write using rolling friction

Answer 2

Actually it's a spherical metal....

While writing on paper, this ball(sphere) rotates...So the ink on one side of the ball(in contact with the ink inside the refill) comes to the other end(in contact with the paper). So, ink in the refill spreads out on the paper... Simply, with the help of rolling friction

Lemme give u another example of it..

Have u seen Attar Bottle???

Well, there is a big roller on one side..If u rub it on ur dress, the ball rotates and the fragrance spreads out on ur dress...The same rolling friction is applied here