Tag Archives: hands-on activity

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?