Intermediate Topic 261 of 1102 States of Matter & Solutions
Capillary Action
Liquid rising in narrow tubes due to adhesion with walls exceeding cohesion.
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In-depth explanation of Capillary Action
Capillary action is the rise or fall of a liquid in a narrow tube, caused by a balance between adhesion to the tube walls and cohesion within the liquid. When adhesion is stronger than cohesion, as for water in glass, the liquid climbs the tube against gravity until the upward force balances the weight of the column. The height is given by h = 2 gamma cos theta / (rho g r), where gamma is surface tension, theta is the contact angle, rho is density, g is gravitational acceleration and r is the tube radius. Narrower tubes produce a greater rise. Capillary action carries water up plant stems and draws ink through paper.
Going deeper: Capillary Action
Key ideas: Use h = 2 gamma cos(theta)/(rho g r) with SI units. For water in clean glass, theta is near 0 so cos is nearly 1. Height is inversely proportional to tube radius, so halving the radius doubles the rise. When theta exceeds 90 degrees, as with mercury in glass at about 140, the liquid is depressed.
Common mistakes and connections: Common mistakes include using diameter in place of radius, or forgetting the contact angle. Another is thinking capillary rise violates energy conservation; the weight of the raised liquid is balanced by surface forces. Dirty glass reduces the rise. Related to surface tension, adhesion and cohesion, meniscus shape and plant water transport.
Visualization of Capillary Action
Capillary rise h = 2 gamma cos(theta)/(rho g r): narrower tubes raise water higher because adhesion to glass beats cohesion. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Water rises about 3 cm in a glass capillary of radius 0.5 mm, whereas mercury is depressed below the liquid level in glass.
Frequently asked questions about Capillary Action
What is Capillary Action?
Liquid rising in narrow tubes due to adhesion with walls exceeding cohesion.
Is Capillary Action a beginner, intermediate or advanced topic?
Capillary Action is a intermediate topic in States of Matter & Solutions. It builds on the vocabulary of beginner topics in this area.
What should I learn before Capillary Action?
Study these earlier topics in States of Matter & Solutions first: Clausius-Clapeyron Equation, Viscosity, Surface Tension.
What comes after Capillary Action?
The next topics in States of Matter & Solutions are Cohesion and Adhesion and Meniscus.
Can I practise Capillary Action with quizzes?
Yes. The interactive lesson includes a self-check question on Capillary Action, and the States of Matter & Solutions quiz draws on every topic in this area.
Where Capillary Action fits in States of Matter & Solutions
Capillary Action is topic 42 of 109 in States of Matter & Solutions.