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Because of Capillary action
Formula:
The height h of a liquid column is given by:
2γ cosθ
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ρgr
where:
γ is the liquid-air surface tension (J/m^2 or N/m)
θ is the contact angle
ρ is the density of liquid (kg/m^3)
g is acceleration due to gravity (m/sec ^2)
r is radius of tube (m)
For a water-filled glass tube in air at sea level,
γ is 0.0728 J/m^2 at 20 °C
θ is 20° (0.35 rad)
ρ is 1000 kg/m^3
g is 9.8 m/s^2
therefore, the height of the water column is given by:
Thus for a 2 m wide (1 m radius) tube, the water would rise an unnoticeable 0.014 mm. However, for a 2 cm wide (0.01 m radius) tube, the water would rise 1.4 mm, and for a 0.2 mm wide (0.0001 m radius) tube, the water would rise 140 mm (about 5.5 inches).
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