When our daughter was born, a colleague said that she was going to teach us a lot about fluid mechanics. It certainly has been true on many occasions. Nowadays, I find entertainment in finding funny analogies between her bathtub games and my research projects.

Yesterday, my daughter took her camera to the bathtub to document her newest toy – a robotic swimming turtle. The turtle has a rotating propeller (an intelligent design, I suppose). We noticed that it was noisier, when filmed from underwater. I could not help but chuckle, because our research group’s current project is related to propeller noise of ships. Who said the bathtub experiments are useless?!

Seriously, though, there is something to be said about learning by playing and experimentation. For example, if I had to explain to a six-year-old why a propeller is noisier in the water than in the air, I wouldn’t know where to begin. Somehow, the fact that the speed of sound is 4.3 times larger, doesn’t strike a six-year-old as a good conversation starter. But a pink swimming turtle does.