Using the “melting ice cube” experiment to let future instructors experience inquiry-based learning.

Ice cubes melting in fresh water and salt water. By Mirjam S. Glessmer

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 and have the future instructors experience inquiry-based learning first hand.

So obviously I brought the ice cubes melting in fresh water and salt water experiment! (Check out that post to read my write-up of many different ways this experiment can be used, and what people can learn doing it). On that occasion the most interesting thing for me was that when we talked about why one could use this — or a similar — experiment in teaching, people mainly focussed on the group aspect of doing this experiment: How people had to work together in a team, agree to use the same language and notation (writing “density of water at temperature zero degree Celsius” in some short syntax is not easy when you are not an oceanographer!).


And this experiment never fails to deliver:

  • you can be 100% sure that at least in one group, someone will say “oh wait, which was the salt water again?” which hands you on a plate the opportunity to say “see — this is a great experiment to use when talking about why we need to write good documentation already while we are doing the experiment!”
  • you can also be 100% sure that in that group, someone will taste the water to make sure they know which cup contains the salt water. Which lets you say your “see — perfect experiment to talk about lab safety stuff! Never ever put things in your mouth in a lab!”
  • you can also be sure, that people come up with new experiments they want to try. At EMSEA14, people asked what would happen if the ice cubes were at the bottom of the beaker. Today, people asked what the dye would do if there was no ice in the cups, just salt water and fresh water. Perfect opportunity to say “try! Then you’ll know! And btw — isn’t this experiment perfect to inspire the spirit of research (or however you would say that in English – “Forschergeist” is what I mean!). This is what you see in the pictures in this blog post.


So yeah. Still one of my favorite experiments, and I LOVE watching people discover the fascination of a little water, ice, salt and food dye :-)

Photo taken by Ulrike Bulmann
Photo taken by Ulrike Bulmann

Btw, when I gave a workshop on active learning last week and mentioned this experiment, people got really really hooked, too, so I’ll leave you with a drawing that I liked:


One of the most exciting things about work travel?

One of the most exciting things about work travel? Staying in tons of different hotels, which all have different opportunities to play with water.

For example at a recent team event, there was this tap with a really efficient aerator, that made the hydraulic jump look even more exciting than usual:


And then at a conference last week, this happened:


Can you see what happened? Obviously, I turned the water on, and the right side of the armature fogged up because of all the cold water going through! (Even though I can assure you: My shower was nice and warm!)

And I am not even going to apologise for how excited I get by observing these kinds of things. Remember the kind of tap I have at home?

2015-11-18 13.15.31

Still the coolest tap I have ever seen! :-)

The importance of playing in outreach activities.

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 – including a lot of bonus materials that didn’t make the cut over at EGU)

What do you think? What makes for the best outreach activities?

My favorite demonstration of the coolest mixing process: Salt fingering!

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 salt fingering!

Self-portrait with salt fingers

As you guys might have noticed, I’ve been playing around with my site a quite bit. My blog has moved to in order to make room for static pages of my favorite experiments or teaching tips right at the landing site What do you think? Good idea? Did you notice anything that isn’t quite working yet or do you have advice or wishes? Let me know!

Temperature-driven overturning experiment – the easy way

In my last post, I showed you the legendary overturning experiment. And guess what occurred to me? That there is an even easier way to show the same thing. No gel pads! (BUT! And that is a BIG BUT! Melting of ice cubes in lukewarm water is NOT the process that drives the “real” overturning! For a slightly longer version of this post check this out).

So. Tank full of luke warm water. Red dye on one end. Spoiler alert: This is going to be the “warm” end.

overturning-ice-1Now. Ice cubes on the “cold” end. For convenience, they have been dyed blue so that the cold melt water is easily identifiable as cold.

overturning-ice-2A very easy way to get a nice stratification! And as you see in the video below, awesome internal waves on the interface, too.


And because I know you like a “behind the scenes”:

I took this picture sitting on my sofa. The experiment is set up on the tea table. The white background is a “Janosch” calendar from 15 years ago, clipped to the back of a chair. And that is how it is done! :-)

Screen shot 2015-11-02 at 3.41.24 PM

A very simple overturning experiment for outreach and teaching

Overturning experiment. By Mirjam S. Glessmer

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 cold water, red dye on the warm pad as a tracer for warm water.

Thermally-driven overturning circulation: Warm water flowing near the surface from the warm pad on the left towards the right, cold flow from the cool pad at the bottom right to left.

A circulation develops. If you drop dye crystals in the tank, the ribbon that formed gets deformed by the currents for yet another visualization of the flow field.

Thermally-driven overturning circulation. In the middle of the tank you see a ribbon of dye, caused by falling dye crystals, being transformed by the currents in the tank.

Lighting is a problem this time of year. I chose natural light over artificial, and it came out ok, I think.

And here is the video:

Ice cubes melting at the bottom of the beakers


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 at EMSEA14, a couple of people asked very interesting questions. One that I totally had to follow up on was this: What would happen if the ice cubes were forced to the bottom of the beakers? Of course we knew what theory said about this, but who cares? I still had to try.

If you have ever tried holding down ice cubes with straws…

…and we have a movie of this! :-)

…you might know that that is quite difficult. So this is the experimental setup I ended up with:

Ice cubes melting at the bottom of a fresh water and a salt water beaker

Zooming out a little bit, this is my fancy equipment:

Screen shot 2014-10-12 at 8.59.10 AM
The camera gets a white skirt over the tripod because the reflection of the tripod is seriously annoying

Zooming out a little more, this is the whole setup:

Screen shot 2014-10-12 at 8.58.46 AM
Chair on table in my winter garden, holding the white-ish oilcloth that serves as background. I should invest in a proper rod for the upper edge of the oil cloth, the current one has suffered a bit…

I know that some people want to try the experiment for themselves, so I’ll hide the rest of the experiment behind the cut, at least until Kristin tells me that she’s done it :-)

Continue reading Ice cubes melting at the bottom of the beakers

Why folic acid might be good for people, but not so good for tank experiments

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 is that the experiment looked like I was using milk. Not what I had envisioned.

Ice cubes melting in fresh water (left) and in iodized-salt-with-folic-acid water (right)

Since I had often before used just regular table salt – which is usually iodized – I was intrigued by the opaqueness that seemed to be due to the addition of folic acid. Or was it? That I had never noticed the milky-ness of the salt water didn’t necessarily mean that it had not been milky before. So this is what the same experiment looks like if regular iodized table salt is used:

Ice cubes melting in fresh water (left) and in iodized-salt water (right). Turbulence in the freshwater beaker due to me stirring (don’t ask)

In the literature it is always recommended to use kosher salt for experiments. Kosher meaning in this context that the salt should be only NaCl with no other additions. I happened to have some at hand after having bought it for the “teaching oceanography” workshop in San Francisco last year (after the salt that I brought for the workshop didn’t make it to the US. Long story). So this is what that looks like:

Ice cubes melting in fresh water (left) and in kosher salt water (right)

In summary: Folic acid is what makes the salt water look opaque – but iodized salt is completely fine for tank experiments. I think it’s tiny air bubbles that cling to something folic acid-y, but I have no clue what is going on. I noticed that the dusty stuff settled down over night (so the top experiment here is a lot clearer than the experiment I ran with the same batch of water the day before), but even the next day the water wasn’t completely clear.

Anyway, now we know. And I came out of this series with more movies of ice cubes melting in fresh water and salt water!

Links to previous posts on the topic after the cut.

[Edit: Using my mom’s iodized, but not folic acid containing, table salt leads to milky water, too. So there you have it. I have no clue what is going on!]

Continue reading Why folic acid might be good for people, but not so good for tank experiments

Melting ice cubes, again

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 forgot. Oh well, at least there is room for improvement still, right?

I always find it fascinating to see how differently the ice melts in fresh water and salt water. Below you see how convection has completely mixed the fresh water with the melt water, whereas the melt water forms a layer on the salt water. You can even still distinguish horizontal currents in there!

The beakers after ice cubes have melted in fresh water (left) and salt water (right)

For everybody who still enjoys watching the experiment: Here is a movie. Top one as time lapse, bottom one in real time, all 8 minutes of it. Enjoy!

The links to the “melting ice cubes” series after the cut.

Continue reading Melting ice cubes, again

Conducting experiments at EMSEA14

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 #EMSEA14 on Twitter.

Our workshop has been represented quite well there, too, so I’ll just post a couple of my own pictures here.

Final preparations: Kristin is mixing salt water
Watching intently the melting ice. As my former boss would say: It’s like watching paint dry.
Except that it is really fascinating and that there are so many things to discuss!
Kristin and I took turns presenting the workshops, which was great. Plus it was really nice to have two instructors walking around, talking to the groups, instead of just one.
Kristin talking about using our favorite experiment to practice applying the scientific method.

For further reading, here are our slides.

Plus there are a lot of post dealing with the exact same experiment after the cut below. And there are two more posts on this exact experiment coming up that are scheduled already, one tomorrow, the other one in two weeks time. And thanks to a very nice family of participants I already have plenty of ideas of how to modify this experiment in the future!

[edit: There finally is a picture of me in the workshop, too, to show that I actually did contribute and not just leave it all to Kristin:

So I did actually do something, too, and not just take pictures. Plus did you notice how there is a EMSEA sign on the podium? There were signs on the doors, too, both on the inside and outside, so one of them was visible even when the door was wide open. Such good thinking of the organizers! Gothenburg University does have a seriously impressive infrastructure in any case: Tables and chairs on wheels so the whole room could easily be modified to suit our needs. Awesome.]