Question

why does the ink from a fountain pen leak at higher alitude

Answer 1

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 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.