Tag Archives: rain drop

A different kind of drop photography today…

After all the professional drop photography I talked about yesterday, here is some of my own from a walk that I took after the amazing and slightly overwhelming experience of giving the laudation speech at the opening of an art exhibition.

Below, I really liked how the wave rings have such different sizes and amplitudes depending on whether they were made by rain drops or ducks (you might have to click the image to enlarge to see what I am talking about).

And below, I love so much about this picture. The long waves with the very small amplitude that are coming into Kiel fjord from some far-away storm. The short waves and small scale turbulence that is created where wave crests just manage to flood a step on the staircase, but the water then flows off it again during the next wave trough. The small speckles made by rain drops. The fact that it seems to almost be summer again because the beach chairs are back! And, of course, that I caught the splash and the flying drops of the wave.

I read this poem by E.E. Cummings on Saturday that really speaks to me. It ends in

“For whatever we lose (like a you or a me)
it’s always ourselves that we find in the sea”
E.E. Cummings

Rain on water — why does each raindrop cause several concentric waves?

When we watch rain falling on a water surface, we observe that each raindrop causes several concentric waves with different radii. In my post on Tuesday I just stated that that was what we observe, but today I want to look into the explanation.

This is what it looks like when it rains on a water surface. Not much surprise here!

Secondary_droplets_01

But when I was visiting my parents last weekend, it started to rain with nice and heavy drops that were few and far between. So I saw my chance, grabbed my camera and ran outside to try and capture exactly what happens when a rain drop hits the water surface. Not an easy task, since everything happens very fast and it’s impossible to anticipate where the next drop will fall, so I had to rely on my camera’s auto focus and just press the trigger as often as possible. And guess what? It stopped raining within a minute! How annoying is that?

But I still managed to capture enough pictures to show you what I wanted to show (see image below):

First, a raindrop just causes a dent in the surface, starting the first circular wave. But if the raindrop was sufficiently large and fast, the surface will bounce back, throwing a secondary (and sometimes tertiary) droplet up into the air. Those droplets will fall in the same spot as the first one, causing the smaller waves.

Secondary_droplets_02

Isn’t this amazing? I’ll definitely work on better pictures in the future, but I am not sure it can be done with my camera.

[Edit 20.4.2016, 12:24. We don’t actually need the secondary and/or tertiary droplets, as Martin pointed out. It is sufficient that the surface gets deformed by the first rain drop, then bounces back and overshoots. When the water that overshot falls back down, this has the same effect as a secondary droplet: to cause a new circular wave just inside of the first one. And of course, the overshooting and triggering of new waves can happen several times, depending on the impact of the initial drop. In a way, my secondary / tertiary drops are just the extreme case of this more moderate version of wave formation.]

To wrap up this post — a bonus picture: Four stages of wave development all captured in one (lucky) shot!

Secondary_droplets_03

Are you looking forward to the next rainy day now because then you can go outside and observe all this cool stuff?