The Golden Ratio and Hydrodynamics

T here are useful and useless golden ratios. We begin with the former. The best way to convert miles to kilometers is to take the next Fibonacci number. Indeed, 5 mi is 8 km, or 55 mi/h (the most important speed limit in the USA until 1995) is 89 km/h. Conversely, take the previous Fibonacci number: 34 km is 21 mi, or 130 km/h (the speed limit in France) corresponds to 80 mi/h (one can always squeeze in extra zeros to the Fibonacci pair 13 and 8); see Figure 1. A justification for this simple rule is that in the Fibonacci sequence