When a thermometer is dropped accidentally, we find the mercury inside the bulb of the thermometer rolling down as small perfect spheres. Raindrops and soap bubbles are also perfectly spherical in shape. A plastic strainer floats on water which is unusual.
All these observations indicate that the free surface of the liquid behaves like a stretched membrane, trying to minimise the surface area. For a given volume, spheres have the least surface area and so raindrops, soap bubbles, drops of mercury assume a spherical shape. In the above case, the force of gravity is found to be negligible. This suggests that the phenomena of the surface behaving like a stretched membrane, is not due to gravity but is of molecular origin.
