Examples of Surface Tension:

(a) You might have noticed that umbrellas, raincoats, tents and canvas have tiny holes in them because they are made of fabrics. Despite this, during rain, the water does not pass through these pores. Did you ever ask yourself why it is so? It is why the surface tension of water prevents it from passing through the fabric.

(b) One of the important consequences of surface tension is that the free surface of a liquid tries to have the minimum possible area. For a given volume, a sphere has the least surface area. Hence the liquid assumes a spherical shape. This is why the raindrops and the mercury globules are spherical in nature. Therefore, the spherical shape of liquid gets distorted if the mass is somewhat larger. This is caused by the force of gravity. Even a large mass of liquid will assume a perfectly spherical shape if the force of gravity is counter balanced. An experiment to verify this was done by Platau. In Platau's experiment, a large drop of olive oil is introduced in a mixture of alcohol and water. The mixture has the similar density as olive-oil. It is observed that the drop assumes a perfectly spherical shape (Figure

c) If you blow a soap bubble at the end of a thin glass tube and allow it to stay in this state for some time, you will observe that it gradually shrinks in volume. This happens since the surface tension of the surface of the bubble tends to reduce the surface area to a minimum.

Figure: Platau's Experiment; the Shape of Even a Large Drop of Liquidremains Spherical if the Effect of Gravity is Neutralised

(d). In this experiment, the effect of gravitational force on the drop of olive-oil is balanced by the upward thrust of the water-alcohol mixture on it.