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?
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 spout. What is going to happen? Watch the movie and find out!
Turns out that now the two water levels in the main body of the jug and in the spout are not the same any more: Since we filled the dense water in through the spout, the spout is filled with dense water, as is the bottom part of the jug. Only the upper part of the jug now contains fresh water.
The difference in height is only maybe a millimetre, but it is there, and it is clearly visible.
Do you see the opportunities for discussions this experiment provides? If we knew the exact volumes of fresh water and salt water, and the exact salinity, we could measure the difference in height of the water levels and try to figure out how much mixing must have taken place when the fresh water was added to the jug. Or we could use the difference in height to try and calculate the density difference between fresh water and salt water and then from that calculate salinity. So many possibilities! :-)
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 mirjamglessmer.com/blog in order to make room for static pages of my favorite experiments or teaching tips right at the landing site mirjamglessmer.com. 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!
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:
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 lower the beam balance towards the water, the large object starts floating! Whereas the other one does not.
And in fact, the small object sinks and the larger one keeps floating.
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 the regular one sinks.
Soft drinks in cans. Who knew you could do science with them?
And then I had those two new tiny cans sitting in my kitchen. My parents came over and we talked about how I am so happy I got those tiny cans, because it is less equipment to lug around when I travel to workshops or courses. And then my mom says that she has never seen the experiment for real. So of course, I have to show her. And what happens? This!
What??
Yes, the regular coke might have sunk a little deeper, but this is really not as impressive as the experiment is supposed to be!
Good thing I moved the cans (which a friend’s friend brought to Norway for me, which I then brought from Norway to Iceland and then back to Norway) with me to Germany… As you see: The large cans still show what I wanted them to show!
Better.
So who knows what is going on here? Too much head space in the tiny cans relative to the amount of soft drink they contain? New formula? Anything else?
And the moral of the story: ALWAYS try your experiments when you are using new equipment before you show them to anyone. Who would have thought that this experiment was not fail safe???
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 to share on here.
We (or I, at least) hardly ever see empty ships. For one, it doesn’t make a whole lot of sense economically to have ships driving around empty, but also the stability of ships is maximal at a certain position of the ship in the water. Therefore people will always try to drive a ship that is neither loaded too full or not enough. But don’t empty ships just look funny?
Ships in the port of Gothenburg
Especially when you see sister ships next to each other where one is full and the other is empty (below).
Ships in the port of Gothenburg
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 that affect the water level? And if so, how?
How much water is displaced by a boat carrying the anchor onboard vs a boat and the anchor in the water? It’s the same amount of water in the jars and the same coins in both pictures…
I like this demonstration because it is so easy and also because so few people get it right when you ask them about it (which is actually a bit shocking).
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:
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:
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 :-)
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!]