Capillary action | Mendeleev

What happens

Capillary action comes from the balance between adhesion to the solid surface, cohesion within the liquid and surface tension.

Water wets clean glass well, so in a narrow glass tube it forms a concave meniscus and rises above the surrounding water level. Mercury behaves differently on glass and forms a convex meniscus.

What changes the process

The narrower the tube, the more important the surface becomes relative to the amount of liquid, so capillary height can become larger.

Why it matters

Paper towels and porous materials use the same family of effects: interconnected small spaces draw liquid through the material. In plants, water transport is more complex and cannot be reduced to capillarity alone.

Go one step further

A useful way to understand this phenomenon is to separate the driving force from the visible result. Temperature, pressure, concentration, surface area and the nature of the materials can each change the rate or the final state. In real systems, several of these factors often act at the same time.

That is why the same phenomenon can look different in a laboratory, in the kitchen or outdoors. The underlying chemistry or physics stays the same, but the conditions change the balance.