When a liquid drop is placed on a horizontal plate, there are two forces acting on that drop of the liquid,
- the force due to surface tension,
- the force due to gravity.
The force due to gravity tends to flatten the liquid drop and spread it out until its surface becomes horizontal. On the other hand the force due to surface tension tries to decrease its surface area and tends to gather up into the form of a sphere.
We know that the gravitational force depends upon the mass of the liquid drop. This is proportional to its volume i.e., to the cube of its linear dimensions. On the other hand, the surface tension depends upon the surface area of the liquid drop, which means that it depends upon the square of its linear dimensions.
As a result, the effect of gravitation is more pronounced on a large drop and the drop gets flattened. On the other hand, the effect of surface tension is more pronounced in the case of a small drop and gave it a spherical shape.
In case of the liquids which do not wet the surface as in case of mercury on a glass plate or water on paraffin wax, a large drop will assume a long elliptical shape with the upper surface in the middle being plane.