Asymmetric propeller blades

On a recent flight to Copenhagen (actually, to Bergen, but that’s another story) I happened to sit with a great view of one of the plane’s propellers. And it struck me how asymmetrical the dark areas caused by the moving propeller above and below the axis looked!

I guessed the explanation would have to be that the propellers were asymmetric in some way, too. Kept me entertained until I saw this:

What could have happened there? Why would there be a seam between completely different patterns of clouds?

I guess there is no reason there shouldn’t be, especially since the cloud / no cloud border is often quite sharp, too. But still, pretty intriguing!

But then a pretty approach to Cph:

And finally: a good view of the propellers. Ha!

And now that I am writing this I am wondering. What’s the difference between asymmetric and asymmetrical? Googling has to wait, I have a plane to catch…

Playing with a ROV

The KiFo owns a ROV that — until now — has never been fully operational. But since I like a challenge (and have a really skilled research assistant who really deserves all the credit) it’s working again!

We first went to test it in a tiny lake on campus.

This was exciting enough, since it seemed to have been leaking on previous attempts.

But this time round it did not, and the lake wasn’t deep enough to test whether it was actually water proof even at increasing pressure.

So off to the Kiel Fjord we went!

And after some careful preparations…

…and a careful launch…

…it worked! :-)

Well, at least until the laptop battery died. But it’s a start! Thanks again for the great work, Nico!!!

Fictitious forces (2/5): Experiencing frames of reference on a playground

How can you be moving in one frame of reference, yet not moving in another?

We talked about the difficulty of different frames of reference recently, so today I want to show you a quick movie on how the seemingly paradox situation of moving in one frame of reference, yet not moving in another, can be experienced on a playground.

My dad on a playground rotator. Moving relative to the rotating disk, yet staying in the same spot relative to the playground.

This is maybe not what you would do with a bunch of university students, but on the other hand – why not?

Playing with water

Sometimes playing with water is all you need to make you happy.

Like on this gorgeous day last December at Möhne Reservoir, the largest artificial lake in western Germany:


That was my godson, btw.. Throwing something, that is, not falling in…

And this was me:


And because I am so happy that I learned how to do that (thank you, Elsa!) I’ll show you a video, too. Maybe some day I’ll talk about the physics behind it, too, but today playing is enough :-)

Refraction of light in moving water — why stuff seems to be jumping around

I was waking along Kiel fjord one morning and noticed a stone “jump” on the ground as waves went over it (and actually, that observation was the motivation to dive into stuff from the last post, too).

I think the stone only looked so curious because the rest of the ground was uniformly sandy and hence didn’t seem to move.


So seeing that jumping stone made me want to draw the optical path, which I’ve animated for you here:


Funny. I think in physics class in school, I would absolutely have hated it had I gotten the task to draw all those different diagrams, and here I really enjoyed it. Maybe because of that jumping stone? Would the right motivation have helped me as a kid to get interested in this? I think it wasn’t that I was not interested in physics, but it would never have occurred to me to sit down on my own to sketch optical paths or anything like that. Now if I could figure out what changed for me, maybe we could use that to make other people interested in physics, too?

Blog post no 500 or: My book has just been published! #superproud

I wrote “Let’s go wave-watching! Discovering oceanography on every stroll” (available in both german and English!) for my god-daughter Pauline and her parents. Pauline wasn’t even six months old then, but I wanted her parents to learn to see everything I see when I look at water, to get as excited about it as I get, and to get Pauline addicted to wave-watching, too, as she grows up. We’ll see how that works out, but now you have the chance to be fascinated and have your eyes re-opened to all the things you theoretically learned about but forgot again :-)


If you are interested, you can find more information on my book HERE. Weren’t you still looking for a christmas present for your niece, your nerdy friend, anyone who should spend more time looking at water?


And also how exciting is it that this announcement also marks the 500th post on this blog? My baby just had a baby ;-)


P.S.: Buy it here: (english | deutsch) or (english | deutsch). Unfortunately, only sells the e-book version and not the print version, but get in touch if you’d like a print version and can’t buy from!

Happy Birthday, dear blog!

Wow, three years ago on this day I started this blog, and this blog post is post no 477. Can you believe that!

And even though I had planned to take the summer off blogging, you see how that worked out — I just had so many pictures that I wanted to share that I didn’t blog for a total of three weeks or so, and then in one day wrote and scheduled bi-weekly posts from early August way into September. When I’m back from my cruise, it’ll be with more actual content, I promise!

So today, here is a picture of a fountain in Sheffield, where I went to a great engineering education conference in summer.

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I like the “infinity pool” look of it, even though there is no ocean behind it, and I find it really fascinating how the spouts seem to be in completely different places than where the water actually comes out when you look through the glass from the side. Isn’t physics just awesome?

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Summer holidays! :-)

This summer, I went sailing the way I used to when I was still a teenager: At Ratzeburger Segelschule. And because I had such a great time, I have to share pictures today. They are to do with water, so not too far off topic for this blog ;-)


A beautiful summer and lots of kids learning how to sail. In recent years, there have been a couple of cool ideas implemented that were not around ages ago when I practically lived there all summer: For example, in order to learn to paddle and steer a sailing boat (before actually learning how to sail it), kids get to collect some 50 plastic duckies out of the lake:


And then, they get to sail. Seeing this particular sail always makes me super happy: It used to belong to my family’s boat! Lots of happy memories connected with this yellow sail.


Therefore, most pictures I took this year involve this sail. Also, the color contrast is nicest.


When there is more wind, things get a little more stressful for the sailing instructors.


But sometimes, when there are not so many kids around and it isn’t too windy, I get to sail in an optimist, too.


But usually there are so many kids sailing at the same time that it’s better to be on a dinghy and shout at them, because most of the time they aren’t all nicely sailing together, but are shooting away in different directions.


Another recent invention is the crowning of “Dödelkönig” – the king of Dödel. A Dödel is someone who is clumsily doing stupid things that he or she should really know better. We now keep a running list of Dödel-points, and at the end of the week, the person who has collected the most points (plus who we think can handle it, not everybody would like to become the center of attention that way) gets crowned, and then “abandoned” on one of the pillars of the old pier. All the other kids then throw in the rubber duckies and the Dödelkönig has to collect them all with a net while swimming from one to the other.

The particular week I was there, we had two Dödelkönige.


And then afterwards, we do the baptism. Since the kids have now learned how to sail, they get welcomed into the community of sailors by having whipped cream put on their head and being thrown into the lake.


A very satisfying feeling for all the sailing instructors to throw in those kids! How far they fly is usually a good proxy for how much they got on our nerves during the week…


And this is what it looks like after all the kids have gone home, when everybody starts to relax and wind down again.



So if you are looking to learn how to sail (or just go sailing in the nicest place there is): Check out Ratzeburger Segelschule!

One glance — do you know which of the bottles is empty?

The other day I was sitting in my conservatory with a friend when I had to take the photo below:

Can you see how one bottle refracts light and the other one does not? What does this tell us about whether there is water in either of those bottles? I met most “normal” people wouldn’t even notice a difference.

I know, I’m a nerd, but I have so much fun “discovering” small stuff like that! :-)

Help me name my book!


If you like my blog, you will LOVE my book. It’s an alternative travel guide: Instead of talking about sights you can see when you visit a city, I am talking about wave and current phenomena that you can spot on puddles, streams, lakes, or the ocean — anywhere, really.

For that, I am showing tons of photos of waves, about half of them annotated to point out the specific things that can be seen on those photos (like I sometimes do on my blog, for example here). While you have seen some of the photos that I show in my book on this blog before, all the annotations are new, and the photos are now put together and into a larger context.

I wrote this book first in german for my niece, but now I am translating it to make it available to a wider readership, and it will be published as print and e-book just in time for summer vacations! How exciting!!! All I still need to do is find a good title. And since you and your friends are my intended audience, who better than you to tell me what kind of title you think fits a book like mine?

I am looking for a title that conveys excitement and discovery related to water, that anyone can experience any time, anywhere. On walks in the city or on the beach, when looking at puddles, rivers, lakes, the ocean. In german (and I am not completely set on this, either), it’s called “Komm, wir gucken Wasser! Beim Spaziergang Wellen und Strömungen entdecken” — which roughly translates to “Come, let’s go water-watching! Discovering waves and currents on your walks”. Which is neither a good translation nor a good title.

Please help me name my book! Leave a comment with your suggestion, I’m super grateful for your input! (And I will consider “Wavy McWaveface’s guide to water-watching” ;-))

P.S.: if you would like to get an email when the book becomes available (it will be available as e-book and in print in german, and as e-book in english), you can let me know HERE and I will let you know!