Capillary rise refers to the phenomenon in which a liquid rises or falls in a narrow tube due to surface tension.
This occurs because of the adhesive forces between the liquid and the surface of the tube, as well as the cohesive forces between the liquid molecules themselves. When the liquid’s adhesive forces to the walls of the tube are stronger than its cohesive forces, the liquid will “climb” up the walls of the tube.
This behavior is most easily observed in thin tubes, and the rise of the liquid is more pronounced in smaller diameter tubes.
Where:
- = height of the liquid rise
- γ = surface tension of the liquid (N/m)
- θ = contact angle (measured from the liquid’s surface to the tube)
- = radius of the tube (m)
- ρ = density of the liquid (kg/m³)
- = acceleration due to gravity (approximately 9.81 m/s²)
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