# Mach number facts for kids

A **mach number** is a number that describes speed. It is a measure of the speed of an object compared to the speed of sound. Mach number is given as a percentage compared to the local speed of sound. For example, half the speed of sound = Mach 0.5.

Where **v** is the speed of the object, and **a** is the speed of sound.

It is named after the Austrian physicist Ernst Mach. When writing a speed as a Mach number, the number comes after "Mach."

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Mach number Facts for Kids. *Kiddle Encyclopedia.*