Non-dimensional numbers may sound like a scary, incomprehensible term reserved for scientists in a laboratory, but you have more experience with them than you know. The Mach number measures the speed of an object relative to the speed of sound, so whether measuring in kilometers per second or miles per hour, Mach 2 is always twice the speed of sound. With the COVID-19 pandemic still raging worldwide, R0 is an important number constantly in the news that measures how many people a person will infect over the course of an illness, whether that time period is days, weeks or months.
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Source: Phys.org