From Disney cartoon animations to symbols on weather apps, the image of a raindrop is instantly recognisable. Universally depicted as having the shape of a tear, this unquestioned assumption is perhaps endorsed by the melancholy we sometimes feel when wet weather arrives. It must be true, mustn’t it?
That’s what I thought too back when I embarked on an undergraduate experiment into the refraction of light through water. But as I illuminated a stream of drops, arcing through the air in my laboratory, I saw not teardrops but perfect spheres.
Not, it turned out, a ground-breaking scientific discovery, but, as a naïve student, this was rather unexpected.
Rain forms either as snowflakes melt or as moisture coalesces around small nuclei in clouds. At this point, suspended in air, a rain droplet is perfectly spherical.
But as the droplet gets larger and larger, gravity takes effect and it starts its decent to earth. Accelerating towards the ground, the sphere gets squashed by the air resistance it encounters head-on. The result: not a sad tear-drop of rain that lands on our heads, but actually something more akin to the top half of a hamburger!
Food for thought the next time the heavens open.