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Raindrops Of Many Sizes

Why are raindrops different sizes when they fall from the sky?

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Photo: peasap (flickr)

A leaf after a rainstorm. You can see the different sizes of the rain drops.

When it’s raining, it may seem that every raindrop is the same–same size, same basic shape, same wetness.

But if you could compare and measure raindrops, you’d find that they’re not all the same size or shape.  In fact, raindrops vary from one to six millimeters in diameter and come in all sorts of shapes.

Why A Difference In Size?

When they first fall from clouds, raindrops are surprisingly large–in rare cases, some are as wide across as a baseball.

So what happens to break these monster drops into many smaller drops of different sizes?

Scientists used to think it was the result of drops colliding and splintering as they fell.

Shattering On Their Own…

But one study has found that although individual large drops do indeed break up into smaller shards, it has nothing to do with mid‑air collisions.  Instead, drops shatter all on their own.

French scientists observed the phenomenon when they used a high‑speed camera to capture drops falling from a nozzle to simulate rainfall.  As it falls from the nozzle or cloud, the drop flattens.

Then it seems to inflate like a balloon.  Finally, after a few milliseconds, the upward pressure of air causes the drop to explode into hundreds of watery bits.

Math Is Always Useful

The researchers created mathematical models to demonstrate that the shattering of individual drops explains why raindrops come in different sizes.

Now, math is always useful–but to really get a sense of how raindrops shatter, you have to see it up close:

Watch: how a raindrop shatters.

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