|Common Representation of a water drop|
Source - free.clipartof.com
|Water dripping from a Tap|
Source - head-first.co.uk
Water drops, smaller than 2 mm in size, take the shape of a perfect sphere.
The drop takes this shape as a sphere is the geometric shape that has the smallest surface area for a given volume (see April 9, 2011 post).
Also, the mass of water contained in a drop of this small size does not experience enough gravitational force for the shape to be impacted significantly. Simply speaking, the gravitational force is much less than the force of the Hydrogen Bonds in a drop of water.
The Shape of Raindrops depends on the size of the drop
|Shapes of Raindrops of fifferent size|
Source - http://en.wikipedia.org/wiki/Drop_(liquid)
As raindrops fall through the air they experience resistance from the air. This resistance is larger for larger drops and is insignificant, like the force of gravity, on drops less than 2mm in size.
As raindrop size grows,however, from the combination of individual raindrops, the air resistance and gravity increase till they force the breakup of the large raindrops into smaller raindrops. These smaller raindrops again start exhibiting the spherical shape and combine into larger drops once again. This process of starting with tiny drops that combine to form larger drops which then break up into smaller drops, only stops when raindrops reach the ground or some structure on the ground.