Capillary action

Capillary action is a phenomenon where liquids flow through narrow spaces without external forces. It’s the reason water climbs up paper towels, and plants can drink from their roots.

Tiny Tubes Create Big Effects

Imagine a super thin straw. When you dip it in water, the liquid climbs up on its own. That’s capillary action at work. It happens because of two forces:

1. Adhesion: The liquid sticks to the sides of the tube.
2. Cohesion: The liquid molecules stick to each other.

These forces, combined with surface tension, make the liquid defy gravity and rise.

History Reveals Capillary Curiosity

Leonardo da Vinci first noticed capillary action, but it puzzled scientists for centuries. In 1660, Robert Boyle observed that a vacuum didn’t affect how high liquid rose in thin tubes. This discovery showed that capillary action was something special.

It wasn’t until 1805 that Thomas Young and Pierre-Simon Laplace cracked the code. They came up with the Young-Laplace equation, which explains how capillary action works.

Math Meets Meniscus

The height a liquid rises in a tube is given by Jurin’s law:

h=2γcos⁡θρgrh = \frac{2\gamma \cos{\theta}}{\rho gr}h=ρgr2γcosθ

Where:

• γ\gammaγ is surface tension
• θ\thetaθ is the contact angle
• ρ\rhoρ is liquid density
• ggg is gravity
• rrr is tube radius

This equation shows why thinner tubes make liquids rise higher. It’s not magic, it’s math!

Capillary Action in the Real World

You’ll find capillary action everywhere:

• Plants: It helps water move from roots to leaves.
• Paper towels: They soak up spills using tiny spaces between fibers.
• Fountain pens: Ink flows to the tip through narrow channels.
• Concrete: It can cause rising damp in buildings.

Even your body uses capillary action. Tear ducts drain excess fluid from your eyes using this principle.

Measuring the Soak: Sorptivity

Scientists use a property called sorptivity to measure how well materials absorb liquids. It’s crucial for understanding things like rising damp in buildings. For example, gypsum plaster has a high sorptivity of 3.50 mm·min^−1/2^, while concrete brick is much lower at 0.20 mm·min^−1/2^.

Capillary action isn’t just a cool science trick. It’s a fundamental force that shapes our world, from the tiniest plant to the tallest building. Next time you see a paper towel soaking up a spill, you’ll know there’s some serious science at work!

Citations:

1. https://en.wikipedia.org/wiki/Capillary_action

Capillary_action (Wikipedia)

Capillary action (sometimes called capillarity, capillary motion, capillary rise, capillary effect, or wicking) is the process of a liquid flowing in a narrow space without the assistance of external forces like gravity.

The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube such as a straw, in porous materials such as paper and plaster, in some non-porous materials such as clay and liquefied carbon fiber, or in a biological cell.

It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid.