Tag Archives: oceanography

Ice cubes melting in salt water and freshwater (post 1/4)

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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, but no explanations yet.

Post 2 will present how I use this experiment in GEOF130, including explanations.

Post 3 will discuss how this experiment can be used in many different setups  and

Post 4 will discuss different purposes this experiment can be used in (seriously – you can use it for anything! almost…).

So, let’s get to the experiment. First, ice cubes are inserted into two cups, one filled with fresh water at room temperature, the other one filled with salt water at room temperature. In this case, the ice cubes are dyed with food coloring and you will quickly see why:

Ice cubes are added to cups filled with water at room temperature: fresh water on the left, salt water on the right.

As the ice cubes start to melt, we can see the dyed melt water behaving very differently in fresh water and salt water. In fresh water, it quickly sinks to the bottom of the cup, whereas in salt water it forms a layer at the surface.

Melt water from the ice cube is sinking towards the bottom in the cup containing fresh water (on the left), but it is staying near the surface in the cup containing salt water (on the right).

After approximately 10 minutes, the ice cube in freshwater has melted completely, whereas in salt water there are still remains of the ice cube.

After 10 minutes, the ice cube in the fresh water cup has melted completely (left), whereas the one in the salt water cup is not gone completely yet (right).

Why should one of the ice cubes melt so much faster than the other one, even though both cups contained water at the same (room) temperature? Many of you will know the answer to this, and others will be able to deduce it from the different colors of the water in the cups, but the rest of you will have to wait for an explanation until the next post on this topic – we will be doing this experiment in class on Tuesday and I can’t spoil the fun for the students by posting the answer today already! But if you want to watch a movie of the whole experiment: Here it is!

(Yes, this really is how I spend my rainy Sunday mornings, and I love it!)

– I first saw this experiment at the 2012 Ocean Sciences meeting when Bob Chen of COSEE introduced it in a workshop “understanding how people learn”. COSEE has several instructions for this experiment online, for example here and here. My take on it in the “on the Cutting Edge – Professional Development for Geoscience Faculty” collection here.

Forskningsdagene are almost upon us

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Preparations for experiments to be shown at the science fair “forskningsdagene” are under preparation.

Forskningsdagene, a cooperation between research institutes and schools, science centers and other educational places, will take place next month in Bergen. This year’s topic is ocean and water, and many interesting activities are being planned.

Today Kjersti, Martin and I met up to test which dyes and liquids are best suited for internal wave experiments. Since the target group on at least one of the days are school kids, conventional substances (like potassium permanganate as dye or white spirit as one of the liquids) might not be the best option. Instead, we went for food coloring and vegetable oils.

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One of our tests – a four layer system with water (green), vegetable oil (turquoise), white spirit and air.

In the end, we came up with many different options and decided that we should probably bring all the bottles so people can play with them, too.  And we should found a company that sells these bottles as nerdy paper weights. I have had one on my desk for a year now and I’m still playing with it, as is pretty much everybody who comes to my office.

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Our selection of different combination of colors and water and oils for internal wave experiments.

But of course the best option wasn’t mentioned until afterwards: Oil and balsamic vinegar! Thanks, Jenny!

Sea surface height and ocean depth

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A hands-on activity in which students use real data to find similarities in the sea surface height and the ocean depth along satellite tracks.

In yesterday’s GEOF130 class, we explored how the sea surface height and the ocean depth are related. All we needed: Sticky notes, scissors and this work sheet (as always – leave a comment if you want more details!).

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When I went and bought the scissors, the lady asked me if I was a kindergarden teacher. I said no, I teach at the university. And that was the end of that conversation…

Heat capacity of air and water

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Hands-on activity to better understand the concept and consequences of heat capacity. Also a great party trick.

Imagine you take a balloon. Any kind of normal balloon. You blow it up. You hold it over a candle flame. What do you think will happen?

Yes – it will burst pretty instantly.

Now imagine you are taking a new balloon. You fill it with water (or, in our case, you fill it about half with water and half with air). You hold it over the flame. What will happen now?

You wait.

And wait.

And wait.

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Balloon, filled with water, being heated above a candle. Note the remnants of the previous balloon (the one that was just filled with air) on the table.

You even take a second candle.

You wait some more.

What happens? Nothing.

And why not? Because water has a much higher heat capacity than air. Meaning you have to put a lot of energy into a small volume of water to warm it up, about 4 times more than you would have to add to a similar volume of air. So the balloon does not get hot quickly, hence the plastic doesn’t get weakened enough for the balloon to burst. In fact, it did not only not get hot quickly, it did not get hot enough at all within the attention span of a typical student or instructor. So, because my students asked nicely, I decided to demonstrate what happens when the balloon is half filled with water, but the flame is directed to an area of the balloon that is not in direct contact with the water. If you can’t imagine what happens, check it out here (if you CAN imagine what happens, I’m sure you will check it out, too…).

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And even more on density

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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 inserted in a jar filled with lukewarm water (movie below). Isn’t this beautiful? And you just wait until we add salt into the equation (and the water) next week!

More on density

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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?

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Soft drinks in cans. Who knew you could do science with them?

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. Thanks to Anna’s friends for importing them for me! As we found out – Red Bull does not work.

How to measure temperature, salinity and density

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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 students can! And it’s also a great opportunity to discuss all kinds of issues with measuring in general, and these properties in particular.

Temperature? Easy! Use the thermal expansion of water! But then wait, does our half liter of water change the temperature of the sample while “measuring” its temperature? Also, how do we know the temperature of the sample if we don’t have a thermometer to begin with?

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A home-made thermometer

Salinity? Really easy! Just evaporate the water and weigh the remaining salt! But what if some of the salt evaporates with the water? What kind of constituents do we have in sea water?

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Sea water is being evaporated in order to investigate the remaining salt.

Density? Since we had our water samples from yesterday’s sea water tasting, all we had to do is find something that floats in sea water without submerging completely, and mark how deep it sinks in the different water samples! But then again, how do we know the density of our samples if we don’t know their temperatures and salinities because the other groups haven’t built those instruments yet? And even if they had, how would we be able to calculate density from it if we didn’t know the equation yet because it had not been established yet?

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Density probe being lifted from a sample.

And what was the most difficult part? To stay focussed on your own experiment while there was cool stuff going on everywhere around you in the lecture theatre. As my office mate predicted: Someone will set the wooden tongs on fire!

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Cool experiments going on everywhere you look!

Tasting sea water

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Hands-on activity on sea water salinity

In the first lecture of the “introduction to oceanography” GEOF130 course 2013, we investigated water samples from four different regions: The Mediterranean, the tropical North Atlantic, the Baltic and Arctic sea ice. Just by tasting their different salinities (40psu, 35psu, 10psu and 5psu, respectively) students figured out which of the samples came from which region. And now what influences salinity in the ocean?