Here are drops in different stages of development
Here the left drop has not detached itself - while the middle and right drops are falling freely. Note that the stem of water attached to the large drop has no sign of fractionation into smaller droplets.
However here, on the left - you can see many small drops forming in the stem. I think this is due to rebound of the stem of water following separation of the larger drop. In the middle the drops have separated and are falling. Also in the middle, the drops behind the large drop are much smaller - perhaps because they were generated by the stem rebound.
On the right - the drop just separated from the column of water
The left drop has gained enough mass to overcome the surface tension that holds the vertical column of water together - and it has started falling. In the middle are many small drops - but one big one at the bottom
From right to left: 1 drop, 3 drops and 5 drops
Three developing drops
Left ot right - a drop that is gaining mass as the rain flows into the stem. In the middle, the stem is separating into smaller drops and on the right the little drops are fully developed
Left - a large drop has separaged and a smaller drop is forming at the end of the stem. In the middle many small drops
Three stages of drop development
Two stems - left, only initially fragmenting while on the right, the smaller droplets have separated
For me, the understand the physics of water flowing down the slope of a roof and resulting in free falling drops is fascinating. The rain water feeds what I call the stem and then at the end of the stem, a droplet forms that slowly increases in mass until the surface tension of the stem is no longer adequate to maintain attachment to the drop.
C. Frank Starmer