Our focus is on financial data, but the field of time series grew up with one foot firmly planted in the physical sciences. We can't examine many of the old toe prints, but some connections are so rich that they deserve at least a word or two.
The speed of sound depends on altitude. If an airplanes flies at sea level, it might run into something, but it could go 761 mph without crossing the "sound barrier." On the other hand, at the normal altitude of flight, you would hit MACH 1 at about 550 mph. This is one reason why commercial airplanes typically fly with an air speed of just under 550 mph.
In class I mentioned the notion of musical beats, and I made a connection to the range of human hearing versus dog hearing. Here is a nice list of hearing ranges for a great variety of animals. Some examples? A human can hear about 64-24,000 cycles/sec, and a dog almost doubles that to 67--47,000 cycles/sec. Chickens are much more limited, just 125---2000 cycles/sec, but mice can hear up to 91,000 cycles/sec. Perhaps this account for their alleged squeaking. Oddly, there are other small animals who can't hear squeaks. The chinchilla, for example, has a top range of 22,800 cycles/sec, about like us.
Many people know that the piano tuner's fork gives a tone of 440 cycles/second, and this corresponds to "A" on the piano. Actually, there are several layers to this onion. First, 440 is the American standard "A" (or more precisely A4 , the 4th octave A), and its ideal 440 contrasts with the older international pitch standard 435.
Later I will make a note about the best depth for a root cellar. It depends on --- yup --- the cycle of cooling and warming of the shallow Earth. Time series and the heat equation make unexpected contact, and (as one finds in 955) the heat equation loops back to our old friend the Black-Scholes equation.
"Washington is the only place where sound travels faster than light." --- C. V. R. Thompson