Final Answer:
Ballpoint pens utilize a sealed ink cartridge with a ball at the tip. The ball rotates and seals the ink, preventing leakage due to changes in air pressure during flight.
Step-by-step explanation:
The primary reason for the difference in behavior between fountain pens and ballpoint pens during flights lies in their ink mechanisms. Fountain pens rely on capillary action, wherein ink flows through a nib due to a pressure difference between the ink reservoir and the surrounding air. However, during high-altitude flights, the reduced air pressure causes the ink in the fountain pen to expand and leak through the nib.
On the other hand, ballpoint pens use a sealed ink cartridge with a small ball at the tip. This ball rotates freely, allowing ink to flow only when pressure is applied while writing. When the pen is not in use, the ball seals the ink reservoir, preventing leaks. Consequently, the sealed design of the ballpoint pen ensures that changes in air pressure at high altitudes don't affect the ink flow.
The mechanism of the ballpoint pen's sealed cartridge prevents ink leakage by relying on the ball's movement to control the ink flow. As the pressure inside the pen remains relatively constant due to the sealed design, changes in air pressure during flight don't impact the ink reservoir. This design principle ensures that the ink remains securely contained, avoiding any leakage even at varying altitudes, making ballpoint pens the more suitable choice for air travel.