The Beauty of Raindrops

Another demanding edition of the photo differences game for you to enjoy! Raindrops on the window pane, lit from behind, make an attractive pattern out of seemingly random droplets.
The science behind this effect is just as wonderful as the droplets look. Both adhesion and cohesion are involved. Adhesion is when the water sticks to another surface like a tiled floor or a table, or to itself: then you get sheets of water. When water forms spherical drops, cohesion is the main factor; this is because water molecules have an in-built attraction to each other. Cohesion results in surface tension, which is the force that holds the dop of water together. Surface tension also explains why it is possible to over-fill a glass with water so that the surface is above the rim of the glass: the water doesn’t flow away because its molecules stick together. If you break the tension, for example wth a spoon or your finger, water will run down the side of the glass.