Capillary Action

physics · water · tiny spaces

Water climbs up. Water can flow upward through a thin tube or narrow space without any help from gravity. This happens because water molecules are attracted to many solid surfaces, like paper or glass, more strongly than they are attracted to each other.

Paper towels work. When you spill water and use a paper towel to soak it up, capillary action is doing the work. The water crawls into the tiny spaces between the paper fibers and spreads throughout the towel.

Plants drink water. Plant roots rely on capillary action to pull water up from the soil into their stems and leaves. The water travels through incredibly thin tubes inside the plant, creeping upward even though water is heavy.

It defies gravity. Unlike most things, water doesn't always fall down because of gravity. In a thin enough space, the attraction between water and the container is stronger than gravity pulling it down, so up it goes!

Molecules stick together. Capillary action happens because water molecules attract each other and also stick to most surfaces. This team effort pulls the liquid along, spreading it into spaces where gravity would normally keep it out.