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Gas Diffusion Limitations

publish date: 2026/05/19 08:39:32.000438 UTC

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If a bottle of strong perfume is opened in a perfectly still room with absolutely zero bulk air currents, why does it still take a noticeable amount of time for a person on the other side of the room to smell it?

The perfume molecules constantly collide with air molecules, forcing them into a slow, zigzag path.

The perfume molecules travel at extremely slow physical speeds of only a few inches per hour.

The molecules must undergo a chemical reaction with ambient nitrogen before moving horizontally.

The scent particles are bound to the floor by gravity until a temperature change occurs.

Correct Answer

The perfume molecules constantly collide with air molecules, forcing them into a slow, zigzag path.

Explanation

At room temperature, gas molecules travel at very high individual speeds (hundreds of meters per second). However, because the atmosphere is crowded with nitrogen and oxygen molecules, the migrating perfume molecules experience billions of collisions every second, forcing them into a highly tortuous, random zigzag trajectory that slows down their net forward progress across the room.

Reference

Basic Physics: A Self-Teaching Guide

Quizzes you can take where this question appears

Diffusion through liquids and gases