Have you ever heard a race car driving past you? It makes a sound like “eeeeeeeeoowwwwww”. That changing sound you hear when a fast car moves past you happens because of a phenomenon called The Doppler Effect.

Now imagine the race car moving in a circle (don't have to imagine that, they do), you hear a sound like “eeeeooowww-eeeoowww-eeeooww” as it moves around. Easy to imagine. Now, what if the race car was moving in a circle on the tilted roof of the Oslo Opera House.(oh)  How does the tilt (or the angle of the tilt) change the sound that you hear? Aha! Not as obvious. This situation is actually really similar to when a star moves around in a tilted orbit where we observe a change in the light produced by the star (instead of sound from a race car).

My research paper tries to determine the effect of the angle of the plane of rotation on the observed frequency shift of a wave source in circular motion.

I conducted an experiment by sticking a small speaker onto the blade of a fan. I played sounds of a constant frequency (“eeeeeeeee”) (I think I've gone blind again) while the fan was turned on so the blades rotated in circular motion. I changed the angle of the fan and recorded the change in sound each time. I found that that sound changes the most when the angle is 0 degrees, and not at all when the angle of the fan was 90 degrees. The frequency at any angle in between depends on several other factors that I discussed in my research paper.