Rayleigh-Plateau Instability: Revisiting my A-Level Physics


To those of you unfamiliar with the UK education system (pre-1998! I think a little different now), A-levels were what you did between the ages of 16-18 at school. I did Physics, Maths and Chemistry.

The Physics A-Level research project was a pretty big deal. You had to think up something you wanted to study, do some experiments and write them up.

Our teacher was Mr Taylor. He was great. We did not seem to follow any sort of syllabus. We just did Physics for two years and came out top bananas. Lots of radioactive stuff. A few explosions. High current electricity. Sparks.

A good friend at school, by far one of the two most talented maths people I have ever known, looked at the traces of pendulums in 3 dimensions. He works at Apple now.

Another guy was looking at drag on various car body shapes. He built a wind tunnel with the models on an electronic balance. He is now important at Jaguar.

Rayleigh-Plateau instability

I looked at Rayleigh-Plateau instability. I did not know that it had a name at the time. This would have been in 1998. Google appeared that same year. I think the only real options were the library and the CD-ROM encyclopedia. I never came across Rayleigh Stability in either of these. Beyond getting some cool high-speed camera shots and procrastinating about the free surface energy of a sphere vs a cylinder, I never really answered my own question, and I have regularly (daily ablutions) wondered about the answer ever since.

Enough nostalgia.

Rayleigh-Plateau instability explains the tendency for a falling continuous fluid stream to break up into droplets at some threshold. Half of the world’s population witnesses this phenomenon daily (standing at toilet/ urinal) and some may have wondered why it happens, as I did as an 18-year old. No doubt Joseph Plateau in 1873 and Lord Rayleigh, shortly after, did too. I feel both of these characters really warrant a moment of your time: Plateau essentially laid the carpet for the development of TV and Rayleigh explained why the sky was blue, amongst (a lot of) other things.

This post is really intended to be a placeholder. Some day I am going to sit down and do the maths and finish that A-Level project!

Not today though.