The substance can be solid particles, liquid droplets, or gases. These clouds are formed from ice crystals, supercooled water droplets, or liquid water droplets. It also assumes that these particles are Poisson distributed among the liquid tin droplets. These millions of tiny water droplets and/or ice crystals form the contrails. Clouds are water droplets or ice crystals suspended in the atmosphere. Mist is a phenomenon caused by small droplets of water suspended in air. Surface tension is responsible for the shape of liquid droplets. Coalescence occurs when water droplets fuse to create larger water droplets. It consists of a tower with spray nozzles, which generate the droplets for surface contact. The updraft carries the super-cooled cloud droplets and very small ice crystals upward. This is due to reactions in the liquid water droplets. This is seen for example in the nucleation of ice in supercooled small water droplets. The first dispersed phase is an emulsion of oil droplets. Clusters can be formed from absorbing metal into helium droplets. Clouds are formed from suspended droplets of water and ice, its solid state.