Category Archives: hands-on activity (easy)

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.

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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!).

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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.

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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 :-)

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Photo taken by Ulrike Bulmann

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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:

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Making a spinningtop from a metal paper clip

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One of my favourite memories of my physics classes at university is of the day when the professor brought in metal paper clips for everybody — to make spinning tops!

When we were playing with the drawing spinning top recently, my mom brought back the paper clip one that I had made some 15 years ago! How is that for a well-organized collection of experimental materials? :-)

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Paper clip and paper clip spinning top

So here is what you do: You unfold the paper clip and turn it into a spinning top! Easy peasy. And if you are keen on all the physics, you can even calculate the angle between the spokes going out from the central axis! 53° or something close is what I remember (and it is confirmed by a quick google search, too). The trick is that the center of gravity has to lie on the rotating axis in the center of the wire that goes around.

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Spinning top made from paper clip

If you want to do this with your students, be nice and hand out the plastic-coated paper clips, they are usually easier to bend. But even with a very imperfect circle and bends that aren’t very sharp or precise, these spinning tops run surprisingly well!

Spinningtop trajectories

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A new physics toy in my house: A spinning top that has a pen as its tip and leaves trajectories as it spins!

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New drawing spinning top and its trajectory.

The trajectories are really cool. Depending on how you spin the spinning top, they look really different. But they all have a common feature: When the spinning top has slowed down, they end in a long swivel away from all the neat spirals, and in the very end they have the small circle as seen in the top left corner of the picture below.

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Close-up of the trajectory in the photo above

See? The radius of that circle is given by the distance from the tip of the pen to the point on which the spinningtop rests, hence it is the same for all the trajectories. But the rest? The trajectories that are really drawn out were those where the tray on which we were drawing was slowly tilted, so they went away from their point of origin, trying to go downhill.

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Trajectories made by spinningtops.

Now if you don’t have such a spinning top, don’t despair. Use the stub of an old pencil (or of one from your favourite Swedish furniture place), pierce it, tip down, through a circular piece of cardboard, and there you go: Your drawing spinning top is ready!

Watch the movie at the bottom of this post to see this trajectory forming:

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Trajectory made by a spinning top.

How do we make climate predictions? An idea for an outreach activity

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Do you need an idea of how to keep your friends and family edutained this holiday season? Then how about using a “mystery tube” to talk about how climate models work? I wrote it up as an outreach activity for GeoEd, the EGU blog’s column on teaching and learning. Find the full text here.

My very first mystery tube

My very first mystery tube

And with this I’ll leave you to play. I’ll be back with exciting new stuff in January. Until then – happy holidays!

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

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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!

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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!

Why does the sun have to be a lot further from us than the moon? A deduction.

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Remember the hands-on demo of the phase of the moon?

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In both pictures: Model of the moon between my fingers on the left, and moon in the background on the right. See how the lit and dark sides of both spheres are in the same position?

Holding a sphere up in the sunlight in the direction of the moon, the sphere will show the same phase as does the moon. Of course it has to, because the sun is so far away that its rays hitting the moon and the ones hitting the sphere are pretty much parallel.

If the sun wasn’t so far away, what would we see?

Schematic of how the Earth, your little sphere you are holding up in the direction of the moon (marked X) and the Moon would be lit if the Sun was not very far away (left) and very far away from Earth and Moon. See how the phase of the moon differs from that of your little sphere when the sun is “close”?

So the only way we can explain that the lit and dark sides of the sphere and the moon are the same is that the light lighting both of them comes in parallel, which can only be the case of the sun is very very very far away compared to the distance of earth, sphere and moon.

Isn’t that a nice little thought experiment?

Temperature-driven overturning experiment – the easy way

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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.

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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! :-)

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Overturning experiment. By Mirjam S. Glessmer

A very simple overturning experiment for outreach and teaching

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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.

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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.

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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:

Getting a “feeling” for ocean currents using adrift.org.au

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It is very difficult to get a feeling of how fast and how far ocean currents can transport heat, plankton, plastic, or many other properties and things. Even looking at maps that depict the ocean currents it is hard to translate those lines into what that actually means in the real world. Here is an activity you can have your students do to help them get a feeling for the scales – both temporal and special – involved here.

Thanks to Dr. Erik van Sebille for creating such a great tool!

Here is the activity I would suggest:

On the website http://www.adrift.org.au [edit: now https://plasticadrift.org] you can release virtual rubber ducks and watch how they are transported by surface currents around the world oceans for the next 10 years.

Can you predict what the plastic distribution will look like 10 years after you released the plastic in the ocean?

  1. Look at the image below. Plastic is distributed all throughout the South Pacific Ocean. Where would one have to release the plastic for the distribution to look like this 10 years later?Adrift_01_ohne_Ente
  2. In this image, the plastic is spread out throughout the Southern Hemisphere over all three oceans. Where would one have to release the plastic to find such a distribution 10 years later?Adrift_02_ohne_Ente
  3. Now, in the image below, plastic can be found in both subtropical gyres in the North and South Atlantic. Where would you have to dump the plastic trash to reproduce such a distribution?Adrift_03_ohne_Ente

 

P.S.: If you use this in teaching, it’s a good idea to bring the un-edited versions of the plots as a backup (so you still see the ducky where the tracer was initially released). Here they are:

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Stream lines and paper towels

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We’ve been talking about stream lines a lot recently (see for example the flow around a paddle or flow around other stuff). I’ve always heard stories about a neat way of visualizing stream lines that I wanted to show on my blog. So I set out to try it, but it just never worked exactly the way I had imagined it should. Anyway, here you go:

We take paper towels and cut an “obstacle” in it. In this case, it’s a drop-shape. The paper towel is set up such that one end is dunked in water, and that once the water has been sucked up a little, it neatly flows down a slope through the towel. In the picture below you see that the water just came over the edge of the cutting boards.

IMG_2102So once a flow has established (and only then, because I wanted to go for steady state stream lines, not some stuff that happens while things are still adjusting), I started dotting dye in to trace the flow:

IMG_2103As you can see, each dot leaves a streak. In this case, though, the streaks are not nearly clear enough for me, so I decided to “recharge” a little further downstream (making sure I put the dye exactly on one of the stream lines, obviously).

IMG_2104And voila! The flow really goes around the object similarly to what we would have imagined. And this is what the finished drop-shaped obstacle looks like:

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stream lines on paper towel

As you see, next time it’s important to make sure there is more paper towel left downstream of the obstacle. We already get interference from the bottom edge of the paper towel where the flow is interrupted.

It’s also important to figure out what kinds of pens work: The picture below is from a test I did at my parents’ which worked a lot better than the pens I tried above.

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stream lines on paper towel

And finally I am not sure how the embossed pattern in the paper towel influences the flow. So maybe I should try and find something with either a smaller pattern or something more regular. Plenty to do still!

So, all in all: Interesting visualization which I am definitely going to try again at some point, but there are still a couple of kinks I need to find fixes for!