CBE 30355 - Lecture Notes - Aug. 29, 2024

Announcements

Class notes

• The Continuum Hypothesis

Goals:

• Know where the continuum hypothesis breaks down.

Reading

• The class notes.
• BS&L, chapter 1

Additional Readings:

In class we talked about the speed of sound. While we won't be doing much acoustics in this class, it's a fun topic. While we usually think of sound propagating through air, in fact it is just as important how sound propagates through water - particularly if you are on a submarine! For just about everything you ever wanted to know about sound in the sea, visit the website here. The history of underwater acoustics near the bottom of this page is particularly fascinating.

Demonstration:

In class today we demonstrated how to tell a raw egg from a cooked one by spinning it. In addition to this effect, cooked eggs also have the interesting property that they tend to "pop up" on their ends when spinning. The mechanics of this phenomenon are actually quite complex, and only recently was solved by Keith Moffatt of the University of Cambridge. More information on this effect can be found here.


A somewhat less whimsical application of egg spinning has recently appeared in Physics of Fluids on concussion research. By looking at what happens to the inside of a raw egg when you spin it vs. impact, the authors conclude that the most likely cause of concussion is shear, not translation. It's when your skull rotates but your brain doesn't... The article is given here.