# Seesawing of standing waves.

Improving one of the experiments run in the GEOF130 lab.

One experiment that has been run in GEOF130 forever is the “standing wave”, where a wave is excited in a long and narrow tank and then, for different water depths, the period is measured and the velocity calculated in order to compare it to the one calculated from the shallow water wave equation.

Traditionally, the standing wave is excited by lifting one end of the tank, letting the water settle down, and carefully putting the tank back down. This, however, means that someone has to lift a pretty heavy weight. So Pierre and I were quite proud of ourselves when we constructed a pulley system last year and now instead of lifting the weight up, someone could hang on a rope instead.

However, this was still hard work, and even though the picture shows a student doing the lifting, for most lab groups it was actually Pierre who did it.

But then this year, we came up with a much simpler solution and I don’t know how we didn’t see this before now. As Pierre remarked: We talk about seesawing standing waves ALL THE TIME. How did it not occur to us that the simplest setup would be a seesaw? So now we have two wooden blocks underneath the tank, one supporting it in the middle and one underneath the end where the operator is standing. So all that needs to happen now is a slight lift of the tank and then a slight downward push to bring it back in the horizontal.

So much easier!

# Water seeks its level.

A solution for the siphon problem of the fjord circulation experiment.

After having run the fjord circulation experiments for several years in a row with several groups of students each year, Pierre and I finally figured out a good way to keep the water level in the tank constant. As you might remember from the sketch in the previous post or can see in the figure below, initially we used to have the tank separated in a main compartment and a reservoir.

But there were a couple of problems associated with this setup. Once, the lock separating the two parts of the tank fell over during the experiment. Then there are bound to be leaks. Sometimes we forget to empty the reservoir and the water level rises to critical levels. In short, it’s a hassle.

So the next year, we decided to run the experiment in a big sink and tip the tank slightly, so that water would just flow out at the lower end at the same rate that it was being added on the other side. Which kinda worked, but it was messy.

So this year, we came up with the perfect solution. The experiment is still being run in a sink, but now a hose, completely filled with water, connects the main tank with a beaker. The hight of the rim of the beaker is set to the desired water level of the big tank. Now when we add water to the big tank, there is an (almost – if the hose isn’t wide enough) instant outflow, so the water level in the tank stays the same.

New setup: A bubble-free hose connecting the tank and a reservoir to regulate the water level in the tank.

This way, we also get to regulate the depth from where the outflowing water is being removed. Neat, isn’t it?

# Traveling circus

Stuff that I  brought to Isafjördur to teach the intro to oceanography.

I’ve been a fan of minimalistic travel for a while. And apparently I was ready for a new challenge: Minimalistic travel but with the full equipment for experiments in oceanography! Sadly I didn’t manage to carry on even though I tried…

Stuff that I’m bringing with me to teach “intro to oceanography”.

It might not look like too much, but you’ll be pleased to know that with this equipment, I can show every experiment I’ve shared on this blog so far (with the exception of the ones in the long internal lee wave tank) plus at least a dozen or so that are still in the pipeline to be published on here (I have lost track of what I have shared and I’m too lazy to look it up now, sorry).

Granted, I did send a list of stuff that I’ll need to Isafjördur, too, and asked them to organize those things for me. But on that list there are only things like paper towels, empty 1.5l bottles or matches – hence things that are very easy to obtain anywhere, but a pain to travel with. I’m bringing all the fancy stuff like high-intensity non-toxic dyes, modeling clay, clear straws (surprisingly difficult to find!), split pins, wooden tongs, heating&cooling pads, an inflatable globe and many more.

So who wants to invite me to come teach at their place? I also “train the trainers” if you want to learn how to do all of this awesome stuff and then teach your students yourself!