|MadSci Network: Earth Sciences|
In real life, raindrops aren't shaped like teardrops. The shape of a falling raindrop is determined by the interaction of hydrostatic, aerodynamic, and surface tension forces. That shape is primarily dependent on the size of the drop. Very small drops, less than 2 mm in diameter, will remain round. The attraction forces between the water molecules (surface tension) are stronger than the other two forces. Larger drops flatten on the bottom as they fall, become rounded on the top, and are wider than they are high. The pressure of the air is greatest on the bottom of the drop, flattening it, and least on the sides, allowing it to bulge. As long as the surface tension balances the hydrostatic (related to the weight of the liquid above the bottom surface of the drop) and the aerodynamic (the force of the air against the bottom of the drop) forces, the drop will remain intact. If the drop becomes so large that surface tension cannot overcome the other two forces, the drop will break into two raindrops. Duncan Blanchard wrote a nice little book some years back called From Raindrops to Volcanoes. It is no longer in print but is available in most libraries. In it, he describes the forces acting on the shape of raindrops, and several very simple experiments that demonstrate the effects of these forces. It's worth looking for.
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