Civil Engineering ⇒ Topic : Surface Tension and Capillarity
Surface Tension and Capillarity :
Consider three molecules A, B, C of a liquid in a mass of liquid. The molecule A is attracted in all directions equally by the surrounding molecules of the liquid. Thus the resultant force acting on the molecule A is zero. But the molecule B, which is situated near the free surface, is acted upon by upward and downward forces which are unbalanced. Thus a net resultant force on molecule B is acting in the downward direction. The molecule C, situated on the free surface of liquid, does experience a resultant downward force. All the molecules on the free surface experience a downward force. Thus the free surface of the liquid acts like a very thin film under tension of the surface of the liquid act as though it is an elastic membrane under tension.
Surface Tension on Liquid Droplet :
Forces on droplet
A hollow bubble like a soap bubble in air has two surfaces in contact with air, one inside and other outside. Thus two surfaces are subjected to surface tension. In such case, we have
p x πd2/4 = (σ x πd)
or p = 2σ x πd / πd2/4
= 8σ / dSurface Tension on a Liquid Jet : Consider a liquid jet of diameter 'd' and length 'L' as shown in Fig below
Forces on liquid jet
Where can I find your questions ?
|The property of a liquid due to which its free surface tries to have minimum surface area and behaves as if it were under tension somewhat like a stretched elastic membrane is called surface tension. A small liquid drop has spherical shape, as due to surface tension the liquid surface tries to have minimum surface area and for a given volume the sphere has minimum surface area.
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