Tag: density

I have had these two words on my mind over the last couple of days: “flexpert” and “pre-industrial”. Some thoughts about them here…

One day in the office at the Geophysical Institute in Bergen last Friday, and for the first time in a long time I am writing a little bit of oceanography and tank experiments again: My colleague Stefanie Semper and I published a SERC “Teach the Earth” activity on “ocean currents and overflows”! This activity is […]

This is the long version of the two full “low latitude, laminar, tropical Hadley circulation” and “baroclinic instability, eddying, extra-tropical circulation” experiments. A much shorter version (that also includes the end cases “no rotation” and “no thermal forcing”) can be found here. Several of my friends were planning on teaching with DIYnamics rotating tables right now. […]

The first experiment we ever ran with our DIYnamics rotating tank was using a cold beer bottle in the center of a rotating tank full or lukewarm water. This experiment is really interesting because, depending on the rotation of the tank, it will display different regimes. For small rotations we get a low latitude, laminar, tropical […]

Today we are doing the melting ice cubes experiment in fancy glasses, because Elin is giving a fancy lecture tonight: The Nansen Memorial Lecture of the Norwegian Science Academy in Oslo! Cheers! We each had green ice cubes in our glasses, but one of our glasses contained fresh water and the other one salt water, […]

A ship that is continuously pulled with a constant force suddenly slows down, stops, and then continues sailing as if nothing ever happened? What’s going on there? We will investigate this in a tank! And in order to see what is going on, we have dyed some of the water pink. Can you spot what […]

When setting up the stratification for the Nansen “dead water” demo (that we’ll show later today, and until then I am not allowed to share any videos, sorry!), I went into a meeting after filling in layer 4 (the then lowest). When I came back, I wanted to fill in layer 5 as the new […]

It’s pretty impressive when a mountain moves through a stratification and generates lee waves. But what I find even more impressive: The waves that travel behind the mountain when the mountain is long gone. See here: This kind of stuff looks more like a numerical simulation than something actually happening in a tank, doesn’t it? […]

Did you seriously think we’d stop tank experiments with only 2-layer systems? Nooo! Today, the plan was to set up a continuous stratification, which I have been planning to do for many years. After fiddling with the setup all morning (do you have any idea how many fittings on all kinds of hoses are needed […]

The main reason why we went to all the trouble of setting up a quasi-continuous stratification to pull our mountain through instead of sticking to the 2 layer system we used before was that we were expecting to see a tilt of the axis of the propagating phase. We did some calculations of the Brunt-Väisälä […]

Now that we do have a really awesome 12-layer 6-color stratification, we obviously had to do the dead water experiment again. This time we chose to include a not-too-happy-looking Nansen on the ship, too! I love this even more than the one we did yesterday!

Did you guess what we needed the stratification for? Yes — we are moving mountains again! :-) What we want to look at: How a current reacts to an obstacle in its way, especially a current in a stratification. But since it is really difficult to set up a current in a tank, let alone […]

The experiment presented on this page is called the “slightly more complicated version” because it builds on the experiment “oceanic overturning circulation (the easiest version)” here. Background One of the first concepts people hear about in the context of ocean and climate is the “great conveyor belt”. The great conveyor belt is a very simplified concept of the […]

A wind stress is applied to the surface of a stratified and a non-stratified tank to cause mixing. This is a pretty impressive experiment to run if you have a lot of time, or to watch the time-lapse of if you don’t. The idea is that a density stratification will make mixing harder than it […]

If you don’t know my favourite experiment for practically all purposes yet (Introduction to experimenting? Check! Thermohaline circulation? Check! Lab safety? Check! Scientific process? Check! And the list goes on and on…), check it out here. (Seriously, of you don’t recognize the experiment from the picture below, you need to read up on it, it’s […]

When you see all our pretty images of currents and swirling eddies and everything, what you actually see are the neutrally buoyant particles that get lit by the laser in a thin sheet of light. And those particles move around with the water, but in order to show the exact movement of the water and not something […]

I haven’t talked about my favourite experiment in a long time (before using it last week in the MeerKlima congress and suddenly talking about it all the time again), because I felt like I had said everything there is to say (see a pretty comprehensive review here) BUT! a while back my colleagues started playing with a […]

Looking at the picture below, can you guess which experiment I am going to do at the MeerKlima.de workshop? Yep, my favourite experiment — melting ice cubes! :-) And I am obviously prepared for several extensions of the classic experiment should the students be so inclined… Now I only need to get the ice cubes from […]

What is the impact of this blog? And who am I writing it for? Those are not questions I regularly ask myself. The main reason I started blogging was to organise all the interesting stuff I was collecting for my introduction to oceanography lecture at the University of Bergen in one place, so I would […]

Sometimes you actually see fresh water layers (see with your eyes, not a CTD or some other instrument) floating on top of denser waters, not only in your kitchen and with the help of dye, but for real. In this case, you see the layers because the shadow of a pole appears twice — once […]

Why is moist air lighter than dry air? This seems pretty counter-intuitive at first, but then really isn’t. I promised to do a post on why moist air is lighter than dry air a long time ago, and wrote it about a year and a half ago (!), but never published it. So here we go […]

How well do people understand hydrostatics? I am preparing a workshop for tomorrow night and I am getting very bored by the questions that I have been using to introduce clickers for quite a lot of workshops now. So I decided to use the hydrostatic paradox this time around. The first question is the standard […]

Using the “melting ice cube” experiment to let future instructors experience inquiry-based learning. I recently (well, last year, but you know…) got the chance to fill in for a colleague and teach part of a workshop that prepares teaching staff for using inquiry-based learning in their own teaching. My part was to bring in an experiment […]

Some time ago, I wrote two blog posts on the importance of playing in outreach activities for the EGU’s blog’s “educational corner” GeoEd. Both have now been published, check them out! Here is the link on EGU’s website (here) and in case that ever stops working, it is also available on my own website (here […]

Last week we talked about misconceptions related to hydrostatic pressure, and how water always seeks its level. Today I’m gonna show you circumstances in which this is actually not the case! We take the fat separator jug we used last week. Today, it is filled with fresh water, to which we add very salty water through the jug’s […]

I am updating many of my old posts on experiments and combining multiple posts on the same topic to come up with a state-of-the-art post, so you can always find the best materials on here. And today I would like to present you my favorite experiment: Salt fingering! Check out the new page I made for […]

For one of my side-projects I needed higher-resolution photos of the overturning experiment, so I had to redo it. Figured I’d share them with you, too. You know the experiment: gel pads for sports injuries, one hot (here on the left), one cold (here on the right). Blue dye on the cold pad to mark the […]

This is an experiment that Martin brought to Ratzeburg and that he let me use on my blog: Using a beam balance to talk about buoyancy. So at first we have two objects hanging on the beam balance, a heavy one with a large volume, and a lighter one with a smaller volume. As we […]

This is why you should always test an experiment before you run it… On recent travels, when I saw that they were serving drinks out of tiny cans, I asked for coke and coke light, because I really like the experiment where you put two coke cans in water and the diet one floats while […]

  Empty ships look weird. Since we talked about the ship-and-anchor thing last week (you know – what happens to the water level when an anchor that was previously stored on board is thrown into the sea) I remembered that I took pictures when I went to Gothenburg in September that I had been meaning […]

Not that this is a big effect in the ocean, but still, it’s a nice demo. A body submerges into the water until it displaces an amount of water that is equal to its own weight. So if you have a ship with an anchor onboard, and then you drop the anchor into the water. Will […]

Because surely there is one more post in this topic? ;-) For those of you who haven’t heard about the “melting ice cube” obsession of mine, please check out the links to other posts at the end of this post. For everybody else’s sake, let’s dive right in! When Kristin and I ran the workshop […]

I had to do the complete series of experiments, of course… The other day I mentioned that I had used salt from my kitchen for the “ice cubes melting in fresh and salt water” experiment, and that that salt was the super healthy one that was both iodized and containing folic acid. And what happened […]

Somehow I am stuck on this demonstration! I can’t let go of this experiment. Last time I posted about it, someone (Hallo Papa!) complained about the background and how I should set a timer and a ruler next to the beakers for scale. The background and timer I did something about, but the ruler I […]

Kristin’s and my workshop at EMSEA14. As I mentioned before, Kristin Richter and I are running the workshop “Conducting oceanographic experiments in a conventional classroom anywhere” at the European Marine Science Educator’s Association Meeting in Gothenburg, Sweden. There is quite an active Twitter crowd around, so you can follow the storyfied meeting or look out for […]

Weird things happening when ice cubes melt. Remember I said that there were weird and wonderful things going on when I last ran the melting ice cubes in salt and fresh water experiment? It is really difficult to see in the picture below (sorry!) but you can probably spot the ice cube floating at the […]

Or why you should pay attention to the kind of salt you use for your experiments. The melting ice cubes in salt and fresh water is one of my favorites that I haven’t written about in a long time, even though (or possibly: because) I wrote a whole series about it last year (see links at […]

How fluid toys can be used to demonstrate principles of fluid mechanics. I guess every attempt to hide that I LOOOOVE fluid toys of any kind is futile. So imagine my excitement when my colleague sent me an article titled “Serious Fun: Using Toys to Demonstrate Fluid Mechanics Principles” by Saviz and Shakerin (2014). While […]

Comparing a rotating and non-rotating dipole. I just realized that I never explicitly showed the difference between rotation and no rotation, even though I do have the footage to do so: Two experiments set up to create a monopole, which both turned dipole. In the non-rotating experiment (which was, by the way, set up carefully in […]

Because sometimes it’s easier to control a computer than rotation, salinity, water and dye. After looking at a non-rotating cylinder collapse the other day, it is time to look at proper hetonic explosions (you know? The experiment on the rotating tank where a denser column of water at the center of the tank is released when […]

Or: This is what happens to a hetonic explosion experiment without rotation. I’ve posted a lot while at JuniorAkademie a while back, so it is hard to believe there are still experiments from that time that I haven’t shown you. But I’ve probably only shown you about half the experiments we’ve done, and there are plenty more […]

Because sometimes one overflow simply isn’t enough. Finn’s group came up with – and ran – an overflow experiment with many different densities and even more colors. While the movie didn’t turn out too well, the idea was pretty awesome. Rolf went ahead and modeled the experiment right away. And because the plume didn’t go across […]

Water running uphill during spin-down – how much more awesome can it get? After hours, when all but the most curious students had left, Rolf and I ran another collapsing cylinder experiment, this time on Rolf’s old disk player turned rotating table. Rolf has a cone-inset for the round tank, and we set a cylinder […]

My absolute favorite experiment ever: salt fingering. I know I’ve said it before about another experiment, even today, but this is my absolute favorite experiment and I still get endlessly fascinated. I’ve written about salt fingering before, and given tips on run the experiment, but today we tried a different setup. We used the same […]

Trying to tweak conditions to force a set number of vortices. We’ve done the hetonic explosion again. This time the group was super careful to calculate the Rossby radius correctly, and then to set up the experiment accordingly. We aimed for a single column like in our tilting of a frontal surface under rotation experiment. We […]

One of my all-time favorite experiments. The salt group got a bit bored from watching ice cubes melt, so I suggested they look at temperature differences for a change, and they ran the “leaking bottles” experiment. Watch a movie combining their four different setups below!

In order to not be in the eddying regime, this time we are rotating our tank as slowly as possible. Since we ran the Hadley cell experiment the other day, I’ve been obsessed with running it again, this time with the slowest rotation possible in order to visualize a different flow regime – one were […]

The unavoidable tank experiment when playing with Rolf ;-) After the first attempt – embarrassingly shown by the instructors – failed miserably, one of our groups ran the overflow experiment successfully. Watch movie below to see the experiment in all its beauty.

Cooling and rotation combined. (deutscher Text unten) I can’t believe I haven’t blogged about this experiment before now! Pierre and I have conducted it a number of times, but somehow the documentation never happened. So here we go today! Martin and I ran the experiment for our own entertainment (oh the peace and quiet in […]

Or, an experiment on this blog often known as “slumping column”. (deutscher Text unten) If you don’t scale your tilting of frontal surfaces under rotation experiment correctly, you get a phenomenon called “hetonic explosion”: the formation of a cloud of baroclinic point vortices. From the densities, the rotation rate, the dimensions etc you can calculate the Rossby […]

Plus all kinds of dyes. (deutscher Text unten) Using the continuous salinity stratification created yesterday, Rolf and Daniel conducted a really cool experiment: They forced internal waves and watched them develop. I’ve converted their movie into a time-lapse; watch it below. Mit der kontinuierlichen Salzschichtung, die Daniel und Rolf gestern gebastelt haben, haben sie danach […]

And watching internal waves – a data-model comparison. (deutscher Text unten) In an experiment similar to the one done by the group looking at the effects of temperature and salinity on density, the wave group, supported by Rolf, started looking at how to create a continuous stratification through internal wave action. Two water masses, one saline […]

Removing a barrier between waters of different densities and watching what happens. (deutscher Text unten) Today, one of the groups performed a classical experiment (shown for example here) – but the awesome thing is that they came up with the planning pretty much by themselves in order to determine the effects of temperature and salinity […]

Luckily I’m not the only one believing that we absolutely need remotely controlled boats! – Zum Glück bin ich nicht die Einzige, die findet, dass wir ferngesteuerte Boote brauchen! Mein Boot hat Hochkonjunktur. D. kann es in einem Tank wenden, der nur etwa 1.5 mal so breit ist wie das Boot lang! Das kann man […]

Eddy in a rotating tank. This is an experiment that Pierre and I ran two years ago in Bergen but that – as I just realized – has not been featured on this blog before. Which is a pity, because it is a pretty cool experiment. Under rotation, vertical fronts with different densities on either […]

Density-driven flow. The experiment presented in this post was first proposed by Marsigli in 1681. It illustrates how, despite the absence of a difference in the surface height of two fluids, currents can be driven by the density difference between the fluids. A really nice article by Soffientino and Pilson (2005) on the importance of the Bosporus […]

Guest post by Kristin Richter! Today I’m excited to bring to you a guest post from Innsbruck, Austria, written by my friend Kristin Richter. Kristin ran the oceanography lab in Bergen before I took over, and she is a total enabler when it comes to deciding between playing with water, ice and food dye, or doing “real” […]

Ha, this is a bad pun. We are modeling the Denmark Strait Overflow – but in a non-numerical, small-scale-and-playdough kind of way. More than a year ago, Kjetil and I ran that experiment with a group of high-school students and when writing a post about a much more sophisticated version of this experiment I realized I […]

 A bit more reflection on cartesian divers. When I wrote the two previous posts, I had known cartesian divers for a very long time in many contexts, for example as something that is routinely used in primary school teaching. While I was aware that developing a correct physical description of such a diver is challenging, […]

Using orange peel as cartesian divers. Guess what my mom told me when we were playing with cartesian divers the other day? That orange peel works really well as a cartesian diver! Who would have thought? And just because we like playing we tried both orange peel and tangerine peel. Watch! Funnily enough, they behave […]

Compressibility of water and air. Today I want to talk about the different compressibilities of water and air. Actually, no, I just want to show you an experiment. One way to visualize that air is a whole lot more compressible than water is to look at cartesian divers. You probably know the fancy ones as […]

About teaching in a language that is a foreign language for both your students and yourself. Most of my teaching so far has happened in English to mainly non-native English speakers with the occasional native speaker thrown in. One thing that I realized recently was that concepts that are definitely not common knowledge at home […]

Students demonstrating the mediterranean outflow in a tank. As reported earlier, students had to conduct experiments and present their results as part of CMM31. Niklas chose to demonstrate the mediterranean outflow – warm and salty water leaving the Mediterranean and sinking to a couple of kilometer’s depth in the Atlantic Ocean. Since I happened to be […]

A tank experiment showing ship-generated internal waves. When entering a fjord from the open ocean by ship, it can sometimes be noted that the speed of the ship changes even though apparently nothing else changed – the wind didn’t change, the position of the sails didn’t change, the settings on the engine didn’t change – […]

Students acting out the process of sound being refracted towards the region of minimum speed. We’ve been talking about refraction lately. Waves get bent in the direction of lower velocity. This holds for light and sound and even ocean waves. However, students find it conceptually difficult to understand why waves are being bent towards lower […]

Tank experiment on a typical circulation in a fjord. Traditionally, a fjord circulation experiment has been done in GEOF130’s student practicals. Pierre and I recently met up to test-run the experiment before it will be run in this year’s course. This is the setup of the experiment: A long and narrow tank, filled with salt water, […]

When students have read blog posts of mine before doing experiments in class, it takes away a lot of the exploration. Since I was planning to blog about the CMM31 course, I had told students that I often blogged about my teaching and asked for their consent to share their images and details from our […]

Students build a device to measure density. As described in this post, I like to have students build “instruments” to measure the most oceanographic properties (temperature, salinity and density). I find that they appreciate oceanographic data much more once they have first-hand experience with how difficult it is to design instruments and make sense of […]

Movie on how the most important instrument in oceanography works. On our cruise on the WHOI research vessel Knorr in 2011, Sindre Skrede (find him on twitter or vimeo for many more exciting pictures and movies!) and I made a movie for his blog, describing the most important oceanographic instrument. We recently translated the movie from Norwegian to […]

A movie of patterns observed in the flow when filling the tank for this experiment. Even though there are tons of scientific things to discuss with this movie, like the different refraction of light in the two layers of different densities, or the filaments, or the restratification processes, I am mainly posting this because I […]

A movie focusing on details of the lee waves in the tank. In this post, we investigated lee waves in a tank in a general way. Here, I want to show a detail of those lee waves: In this movie, the concept of hydraulic control becomes visible. On the upstream side of the mountain, the […]

How internal waves in the ocean can be spotted on the surface. Under certain conditions, internal waves in the ocean can be spotted at the ocean’s surface due to changes in surface roughness or to the movement of floating foam or debris. They can be spotted if half their wavelength is longer than the distance […]

Lee wave experiment in a large tank with a moving mountain. In this previous post, we talked about internal waves in a very simple experiment. But Geophysical Institute has a great tank to do lee wave experiments with that I want to present here (although it doesn’t seem to be clear what will happen to the […]

Internal waves are shown in simple 0.5l bottles. Waves travel on the interface between fluids of different densities and the phase speed of those waves depends on the density difference between the two fluids. The simplest way to demonstrate this in class can be seen below – two 0.5l plastic bottles are used, one half-filled […]

Different didactical settings in which the “ice cubes melting in fresh and salt water” experiment can be used. In part 1 and 2 of this series, I showed two different ways of using the “ice cubes melting in fresh water and salt water” experiment in lectures. Today I want to back up a little bit […]

The “ice cubes melting in fresh water and salt water” experiment the way I usually use it in class. — Edit — For an updated description of this experiment please go to this page! — Edit — You might remember the “ice cubes melting in fresh water and salt water experiment” from a couple of […]

Experiment to visualize the effects of density differences on ocean circulation. This is the first post in a series on one of my favorite in-class experiments; I have so much to say about it that we’ll have to break it up into several posts. Post 1 (this post) will present one setup of the experiment, […]

My favorite experiment. Quick and easy and very impressive way to illustrate the influence of temperature on water densities. Today in the “introduction to oceanography” (GEOF130) we conducted my favorite experiment ever: Cold water in one of the small bottles is dyed blue, hot water in the other small bottle is dyed red. Both are […]

Extremely simple experiment to illustrate the effect of density differences. At room temperature, will coke cans float or sink in freshwater? And how about coke light? Btw, this experiment is only easy if you are in a country where you can get the right soda brand both in normal and in light version in cans. […]

Three in-class experiments run in parallel. Great if you want to discuss how properties are measured and what kind of difficulties you might encounter. Temperature, salinity and density are the most important properties in physical oceanography. Measuring them with a CTD is easy. But can you, using basic household items, build instruments to measure those properties? My […]