Abstract
The study of collision and coalescence mechanism for water droplets in cloud has a large importance
because its represented major process in formation rain in warm clouds .
In this study the, the relationship between the efficiency of coalescence ( coa E ) and the radius of droplets
in warm clouds had been studied by taking different radius of large droplets ( R ) ranged between
(60 to 100m) with groups of small droplets ( r ) that has radius ranged by (5 to 20 m) because these
values represented nearly the range of radius of droplets occurred in warm clouds .
The results appears that coalescence efficiency proportional directly with the radius of large droplet and
inversely proportional with radius of small droplet