Question

Why does a fountain pen leak when it is taken high up in altitude? Does fountain pen require friction to write?

Answer 1

The fountain pen leak at high altitudes is because of low air pressure. The ink inside the fountain pen has high pressure compared to the low atmospheric pressure at high altitudes. So the ink flows out of the pen

The atmospheric pressure decreases with altitude because gas molecules which make up the air concentrate near lower altitude in response to Earth’s gravity. Hence, air pressure is low at higher altitudes. Fountain pens or toothpastes brought to higher altitudes from lower altitude regions contain air at high pressure (equal to that of the low altitude region it is brought from). Due to this difference in air pressure, the air inside the pen forces the ink to come out. This equalizes the air pressure inside and outside the pen (Boyle’s Law: PV=constant). Hence the pen leaks. Similar is the case for toothpaste.

fountain pen rely on capillary action, rather than
friction, to write. Capillary action is the intermolecular
attractive force or surface tension that causes water
molecules to follow molecule-by-molecule out of fountain
and nibs. As a result, both styles of pens
effortlessly glide over the page and give handwriting a
unique character.