# Mariotte’s bottle: A nifty trick to control “reservoir height” in #dropphotography

In earlier posts on drop photography, you might have noticed that the reservoirs for the water that drops out and creates the beautiful liquid art has a weird cork on top, sealing it off, and a glass pipe sticking through. I’ve been wanting to explain what that’s all about for a while, but had to finally draw the picture for our liquid art workshop yesterday. So here we go!

Above, you see Wlodek adjusting something about it, and below is my sketch: A Mariotte’s bottle!

Very useful little thing to control pressure in a reservoir, and with pressure the “reservoir height” that is felt at the outflow, even though the reservoir height is actually changing. Basically, it’s a way to trick the system to feel a constant hydrostatic pressure.

Below on the left, you see the bottle when it has just been filled. A cork is sealing the top of the bottle, except that the inside and outside are connected by a pipe on top and the outflow at the bottom. Initially, the water level inside the top pipe and the bottle are the same and the pressure on both water surfaces is the atmospheric pressure.

As water flows out of the bottle, the water level in the bottle starts sinking. The head space (the air inside the bottle above the water) is sealed off from the outside, so as the water level sinks, its volume increases and its pressure (and thus the pressure on the water surface inside the bottle) sinks. In the middle plot below you see what happens then: The water level inside the pipe starts sinking to compensate for the missing volume inside the bottle.

Eventually, air starts bubbling out of the pipe into the headspace, and the water level inside the pipe is at the very bottom end of the pipe (right plot above). The pressure at this level (marked as A) is now atmospheric pressure, not only at the bottom of the pipe, but throughout the whole bottle. And the pressure at this level will continue to stay at atmospheric pressure levels for as long as the water level is still higher than the bottom end of this pipe. Occasionally, air will bubble out of there to compensate for further outflow.

So at the outflow, we always have the hydrostatic pressure relating to the height from B to A, no matter how much or little water there is in the reservoir. That means that all drop pictures in a series will have similar conditions, even as the reservoir is slowly getting empty. How cool is that? I love those kind of things. So simple, yet so efficient! :-)

# #DropPhotography. Art or physics? Art AND physics!

When I take pictures of drops, they look like the picture below (which I showed in a blogpost yesterday), but I see tons of physics everywhere. Ring-shaped waves! Drops jumping up due to surface tension! Interference pattern of overlapping waves! And much more.

When Wlodek Brühl takes pictures of drops, they look like below. As an artist, to him it’s all about composition and inspiration and expression.

And when we work together, lots of interesting things happen. Do you want to see our art and science collaboration in action? Then come join one of our workshops at Digitale Woche Kiel, both on September 8th, 2019, one at 11-13 and the other at 13:30-15:30. Could you think of anything more inspiring to do on a Sunday? :-)

# Involuntary #dropphotography today

When I decided that I was going to stop under a tree for a while to let the shower of rain pass before heading home, the weather looked like this.

Not even half a minute later, I was very happy I had stopped! Because the wave watching got a lot better as the wind drove larger wave over the lake, and also because the rain got a lot heavier and I was semi-dry under the tree. But that makes for some fun drop photography!

All those little wave rings look so cool!

And it’s impressive how a little wind quickly changes the wave field on the lake, too.

# Some #wavewatching in Manchester

I’m in Manchester for Science in Public 2019 and I couldn’t help myself, I had to do some wave watching.

To be fair, though: These pictures really don’t do Manchester justice as a city. It is such an amazing city! Last time I was here, I spent a whole day exploring four historical libraries that were breathtakingly beautiful, and I would totally recommend you do the same if you are here, even before wave watching. And that is saying something! And I love all the architecture here, and the Science and Industry Museum! But my blog is about Adventures in Oceanography and Teaching, so I am not showing you that side of the city here, only the river Irwell and some reflections of buildings in it.

First: A storm drain run-off into the river. Do you see the waves radiating away from where the water drips into the river?

And here is a “before” picture of the river…

…so you appreciate the “after” picture with all the cute little waves made by raindrops. (No irony here — I really enjoyed watching this!)

And it does look pretty, doesn’t it? I especially like the wave rings on the boundary between the dark reflections of the buildings and trees, and the brighter reflection of the sky, blurring the line, bringing the sky and the city together…

Oh, and one of my favourite wave pattern: The V-shaped wake of a row boat and the pairs of eddies, rotating in opposite directions, where the oars pushed through the water!

# An art & science collaboration with Wlodek Brühl: #dropphotography

If you are here because you saw my title or talk at the Science in Public conference in Manchester and are curious about #dropphotography as a form of art&science collaboration in scicomm — a special welcome to you! If you are here for any other reason — welcome anyway! :-)

One of my favourite pet projects right now is the #scicomm collaboration with the artist Wlodek Brühl.

The idea behing the collaboration is very simple: Wlodek does awesome drop photography like what he showed in his recent exhibition, or the picture below: Drops falling into water, creating sculptures that he captures with digital photography.

I, on the other hand, use the opportunity of having people fascinated and mesmerised by this art, and curious to learn more about it, to talk about — what else? — physics! :-)

For one example of what that collaboration looks like in practice, check out my speech at the opening of his latest exhibition. We have a workshop coming up this autumn that we will run together, as well as other exciting projects which are, unfortunately, still secret. It’s going to be awesome, though!

But back to physics: Creating the exact sculpture you want requires enormous precision. This is what the setup looks like: Reservoirs above a vessel in which the drops fall. And a complex setup of flashlights and a digital camera, all coordinated by a custom-made piece of software.

The most important thing influencing the momentum with which a drop hits the water below is the height it falls from. Below, pictures are taking at constant intervals after drop release, yet you see that the for each new picture, the drop fell a little further than it did in the previous interval — it fell a little faster due to acceleration of gravity. Thus the longer you let a drop fall (i.e. the higher the drop falls from), the more it will accelerate, bringing more energy into producing a fountain.

The next thing that needs to be very precisely controlled are the opening times of the valves that release the drops. Not only when they open, but also for how long. Consider opening times of the valves in the picture below, left to right: 50, 55, 60, 70  milliseconds (The series of pictures on the left you know already from the “acceleration of gravity” pic above).

Depending on how long the valve is opened, different volumes of water are released, forming different drops. Easy to imagine that this will lead to different fountains once the drops hit the water below!

So what happens exactly once the drop hits water? The water surface gets deformed as the drop pulls it downwards. Due to surface tension, it then bounces back up, bringing up a column of water, that then collapses back down. And all these disturbances radiate ripples away from the original point of impact — capillary waves! (Capillary waves are super interesting because they behave very differently from “normal” gravity waves, but that’s a topic for a different post!)

But so that’s how fascinating it is to watch just one drop falling into water. Now imagine several drops falling one after the other, such that a second or third drop hits the column rising up after the first drop already hit the surface? That’s what makes these interesting umbrella shapes:

As you can imagine, there are tons of parameters you could vary now. Not only fall height and drop size, time lag between drops, number of drops that fall, but also viscosity of the fluid, shape of the bowl the drops fall into, all kinds of things. And that’s only using the easiest setup! You could also imagine using several valves, or air pressure to shoot drops with more momentum, or even have water shooting up from below (all of which Wlodek has done!).

And then, of course, depending on when exactly you choose to take a picture of the sculpture, you will see it in very different stages of formation and decay. You see the attempt of surface tension to minimise disturbances, instabilities that still form along the rim of the umbrellas which ultimately burst into many different small droplets…

Do you see the potential to talk about physics pretty much forever here? I love it! :-)

# Opening speech for Wlodek Brühl’s art

You might remember that I had the honour of giving a speech at the opening of Wlodek Brühl’s art exhibition back in spring. Preparing my presentation for the Science in Public conference in Manchester next week (that I am immensely looking forward to!), I noticed I never posted the speech. Below is what I sent Wlodek in advance to prepare him for what I might say:

Lieber Wlodek, sehr geehrte Damen und Herren,

es ist mir eine große Ehre, die einleitenden Worte auf dieser Vernissage, dieser Eröffnung der Ausstellung von Werken Wlodek Brühls, zu sprechen und Sie hier Willkommen zu heißen.

Obwohl genau das die Wortbedeutung von „Laudatio“ist, ist mir ausdrücklich untersagt worden, den Künstler zu loben – vom Künstler selbst. Also werde ich heute lieber über Physik sprechen. Wenn Sie die Bilder von Herrn Brühl betrachten, denken Sie dann nicht auch sofort und unausweichlich über Physik nach?

Springbrunnen kennen wir zu Genüge, in Pfützen fallende Tropfen auch. Und letztendlich sehen wir hier genau das, wenn auch mit etwas mehr technischem Aufwand umgesetzt, um die entstehende Skulptur ganz genau beeinflussen zu können. Deshalb kommen uns die in diesen Fotografien gezeigten Formen seltsam vertraut vor – richtig gesehen haben wir sie aber noch nie. Auch wenn genau solche Strukturen um uns herum existieren (und dabei ist anzumerken, dass jede dieser Skulpturen einzigartig ist, wie auch keine Schneeflocke exakt einer anderen gleicht), mit bloßem Auge können wir sie nicht erkennen, weil sie nur für Bruchteile von Sekunden bestehen und unser Gehirn schlicht zu langsam dafür ist. Solche Skulpturen trotzdem bildlich festzuhalten gelingt mit vielen technischen Tricks: Mit computergesteuerten Ventilen, die Tropfen so auslösen, dass sie genau mit anderen Ventilen, dem Blitzlicht zur Beleuchtung und dem Auslöser der Kamera abgestimmt sind. Sichtbar werden dann Skulpturen und nicht nur verwischtes Wasser, weil die Skulpturen in einem stockdunklen Raum für ein Bruchteil einer Sekunde von einem Blitz beleuchtet werden, so dass trotz der längeren Belichtungszeiten der Kamera auf dem Bild nur dieser eine, enorm kurze Moment sichtbar wird, in dem es – exakt zum richtigen Augenblick – geblitzt hat.

Aber kommen wir zur Physik. Wenn Sie diese Ausstellung bei – aus physikalischer Sicht – einfacheren Bildern anfangen und sich dann langsam steigern möchten, würde ich empfehlen, in diesem Raum zu beginnen.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Hier drängt sich mir zum Beispiel die Frage auf, warum die Skulpturen von unten aus dem Wasser nach oben zu wachsen scheinen, bevor sie sich ausbreiten, verzweigen? Der Schlüssel hier ist die Oberflächenspannung des Wassers. Die Wasseroberfläche, durch einen fallenden Tropfen nach unten ausgelenkt, schleudert den Tropfen wie ein Trampolin wieder nach oben und wölbt sich selbst hinterher, bäumt sich auf, bevor sie wieder in sich zusammen fällt. In einigen der Bildern kann man diesen nach oben geschleuderten Tropfen sogar noch erkennen.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Und dann sehen wir im oberen Teil vieler der Skulpturen Formen, die wie Schirme oder Leselampen aussehen, oder wie Vasen. Warum sind diese Strukturen manchmal nach oben geöffnet, manchmal nach unten, manchmal voller filigraner kleiner Ärmchen am Rand? Das sind eigentlich schon zwei Fragen in einer. Die Form der Kelche hängt davon ab, wie schnell sich zwei Tropfen aufeinander zu bewegen und ob ein großer auf einen kleinen trifft oder umgekehrt. Die kleinen Ärmchen sind Instabilitäten, die entstehen, kurz bevor der Schirm zerfällt. Schirme ohne Ärmchen sind also genau in dem Moment belichtet und eingefangen worden, als noch alles stabil war. Bruchteile von Sekunden später wären auch sie instabil geworden.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Und wenn Sie mit diesem Blick durch diese Ausstellung gehen, werden Ihnen noch viele andere Fragen kommen. Manchmal, zum Beispiel, sehen wir Skulpturen, die auf zwei Säulen zu ruhen scheinen. Wie sind diese wohl entstanden? Und dann sind die Skulpturen farbig – und die Farben sind direkt in der Aufnahme entstanden und nicht nachträglich digital eingefärbt. Das wurde in diesem Raum durch farbige Blitze gemacht, in den anderen beiden Räumen durch eingefärbtes Wasser.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Wenn Sie als nächstes dann in den Raum dort hinten weitergehen, sehen Sie Skulpturen, die an der Wasseroberfläche gespiegelt sind. Durch die Spiegelung hat man auf ein mal zwei unterschiedliche Perspektiven auf die Skulptur und kann jetzt Strukturen noch genauer beobachten, um über sie nachzudenken.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Im dritten Raum sehen Sie die neuesten Kunstwerke von Herrn Brühl, die vor wenigen Wochen erst entstanden sind. Hier wird die Physik noch komplexer. Zusätzlich zu all dem, was ich gerade schon über fallende Tropfen erzählt habe, kommen hier noch mit Druckluft angetriebene Fontänen hinzu. Und zwar einfache, die in der Mitte der Skulptur gerade nach oben schießen, und dann auch solche, die aus einer sich drehenden Turbine nach oben und außen geschleudert werden, erst einen Kelch bilden und dann in einzelne Tentakel zerfallen. Und in diesen Bildern sieht man manchmal auch die Schlieren und Pigmente der verwendeten Farben!

Wenn man wollte, könnte man an jedem einzelnen Kunstwerk stundenlang beobachten, grübeln und diskutieren. Wie sähe eine Skulptur wohl aus, wenn ein Tropfen größer gewesen wäre als er war, oder etwas später gefallen, oder vielleicht aus einer anderen Höhe? Oder wenn das Bild Sekundenbruchteile eher oder später gemacht worden wäre und uns damit einen anderen Zeitpunkt der Entwicklung und des Zerfalls der Skulptur gezeigt hätte? Was, wenn anstelle von Wasser zum Beispiel mit Honig gearbeitet würde? An Ihren Gesichtern sehe ich, dass diese Fragen Sie schon jetzt faszinieren. Das ist genau die Physik, die ich speziell bei den Tropfenskulpturen von Herrn Brühl so fesselnd und aufregende finde!

Ich wünsche Ihnen viel Spaß in dieser Ausstellung – dass Sie die beeindruckende Kunst von Herrn Brühl als Kunst genießen können, aber dass Sie sich vielleicht an manchen Stellen auch fragen, wie genau er es wohl geschafft hat, solch ein Meisterwerk entstehen zu lassen. Ich bin mir sicher, dass Herr Brühl Ihnen gerne Rede und Antwort stehen wird! In diesem Sinne: Herzlich Willkommen!

# Vernissage of “liquid art”: The perfect opportunity to combine art & physics to do some scicomm!

If you don’t want to “preach to the choir”, how do you, as science communicator, reach new audiences occasionally?

One way that I tried today is to give the (invited, I swear!) laudation at the vernissage of Wlodek Brühl‘s exhibition on “liquid art“. The idea was that visitors would mainly come to the event because they are interested in art itself, but that I will try to give them a new perspective on the art by exposing them to the science behind it. Which I think is a pretty cool concept!

Yesterday, I got a sneak peek into the exhibition which features new art that isn’t even two weeks old! I took pictures of some of the art to show on this blog (with Wlodek’s permission!).

Let’s start with a sculpture that isn’t even part of the actual exhibition but that is displayed in my living room (and I love it!!!): A very simple drop sculpture. A drop fell onto a water surface. Due to surface tension, the water surface deformed, got pulled down, bounced back, overshot, and a drop shot up again, pulling a thin trail behind it. As the drop was flying upwards, it got hit by a second drop which fell straight on it. That second drop splattered into this umbrella, which is starting to disintegrate into small instabilities that form tiny filaments. A fraction of a second later and the whole thing would have collapsed and look totally different.

My picture of art by Wlodek Brühl, taken and published with kind permission.

That’s part of the art of capturing these sculptures: timing. Not only does one need to be super precise in the timing of drop releases, one also needs to capture the exact right moment to light the dark room with a flash, which is a lot shorter than the exposure time of the camera. Of course it’s all controlled by a computer!

But here is an impression of the exhibition itself.

My picture of art by Wlodek Brühl, taken and published with kind permission.

I’d like to start out with some of the older art from 2016 which is easier to explain: “Simple” drops like you see to the right of the door above, then double pillars to the left of the door, and then reflections, before we move on to the kind of art that you saw at the top of this post.

In the picture below, what happened is pretty similar to what happened in the picture above: A drop fell, bounced back up again and was hit by a second drop. The second drop hit the first one when that one was still fairly fast, therefore the vase-like structure. (And don’t you just love the waves that you see on the water surface? I feel like I see the actual dynamic process of the surface rising up!)

My picture of art by Wlodek Brühl, taken and published with kind permission.

Or below, another similar setup, except here the drops collided in such a way that the larger, bottom one formed an umbrella-like shape, whereas the upper one rose as a vase.

My picture of art by Wlodek Brühl, taken and published with kind permission.

It gets more complicated if two drops are released simultaneously as below, and then a third one hits them in the middle with a little time delay to form the umbrella, and a fourth drop is still falling down and hasn’t reached the sculpture yet.

My picture of art by Wlodek Brühl, taken and published with kind permission.

So much for the “simple” structures, now on to more complicated ones. The ones below are similar in their setup to the ones above, but now they are photographed against a black background and in a large, black dish. Therefore we see the reflection of the sculpture on the water surface. This lets us look at different structures within the sculpture from two angles, making it even cooler to think about all the physics going on here!

My picture of art by Wlodek Brühl, taken and published with kind permission.

But now on to stuff done with more fun toys:

These are the newest works of art that Wlodek did only within the last two weeks! I personally prefer the translucent, fragile, light sculptures like the one in my living room, but I can also really appreciate those bouquets of spring flowers for their dynamic and lively shapes.

My picture of art by Wlodek Brühl, taken and published with kind permission.

Below I am showing a larger version of the sculpture to the very right above. In these new sculptures, Wlodek isn’t “only” working with drops, but now he has started to incorporate colored jets that are driven up by pressurised air. See how the yellow central jet broke through the umbrella formed by the orange drop that dripped on it from above?

Additionally, Wlodek is building vases around the bouquets by pushing dyed water through a rotating turbine. This vase breaks up into tentacles when it gets unstable!

The sculpture below is called “sundae with umbrella” and I cannot un-see this!

My picture of art by Wlodek Brühl, taken and published with kind permission.

But mostly I see flowers, specifically orchids. Below, the yellow drop from the top didn’t hit the green-ish jet from below completely center, therefore the latter broke up and seems to be turning towards us, wrapped in the orangey-yellow vase that has become very unstable on one side, but not so much in the back. Don’t you just love how the rims bulge together due to surface tension?

My picture of art by Wlodek Brühl, taken and published with kind permission.

In any case, I had a blast, even though, judging from the picture below that shows me giving the laudation, it doesn’t seem like it. Do I always look this serious? But the feedback I got was that everybody enjoyed looking at Wlodek’s art through a physics lense, at least after they got over their initial shock that they would have to listen to physics on their artsy Sunday morning. So this is definitely a scicomm format I want to explore more!

Me (in stripes) with the artists Regine Hahn (left) and Wlodek Brühl, as well as the host, chairwoman of Kunstkreis Preetz. Picture by Frauke Voitle, used with permission.