We draw them pointed at the top,
a teardrop with a rounded base,
but no real raindrop, as they drop,
has ever worn that kind of face.
The smallest drops are round as beads:
their surface pulls in tight and neat,
and drawing in, the water needs
the smallest skin: a sphere, complete.
But bigger drops fall faster, so
the air beneath them pushes hard
and flattens them from down below:
a burger bun, not a greeting card.
And once they grow past four or five
millimetres wide, the air
blows in their base, a bag, alive,
that bursts to droplets then and there.
Nor do they speed the whole way down:
the faster, the more air holds back,
until, long before the ground,
drag matches weight, and holds their track.
So big drops hurry, nine or so
metres a second; small ones creep;
and that is why the rain, you know,
can sting, but never cuts you deep.
So when you draw the rain, be fair:
draw beads for drizzle, buns for storm,
and leave the teardrop hanging there
from tap and leaf, its proper form.
A small experimentSurface tension versus gravity
- Put a tiny drop of water on the paper. Look at it from the side, at eye level.
- Add a medium drop next to it, then a big one, as large as you can make.
- Compare their shapes from the side.
- Gently push two small drops together with the straw and watch what happens.
What's going on?
Tiny drops are almost perfect beads, because surface tension wins easily at small sizes. Big drops slump into flat puddles, because their weight grows faster than the pull of their surface. Two drops merging snap into one rounder drop, since one drop has less surface than two. A falling raindrop is fighting the same battle, with the push of the air in place of the table.