The Mach number is a dimensionless quantity that compares the speed of an object to the speed of sound in the surrounding medium (usually air). It is named after Austrian physicist Ernst Mach, who studied the behavior of projectiles and shock waves.
Mathematically, Mach number (M) is defined as:
Mach number (M) = Object’s speed / Speed of sound in the medium
- If M < 1, the object is moving at subsonic speeds.
- If M = 1, it is moving at sonic speed (equal to the speed of sound).
- If M > 1, it is moving at supersonic speeds.
- M ≥ 5 is referred to as hypersonic.
The speed of sound varies depending on the medium and its conditions, such as temperature and pressure. For example, in air at sea level and room temperature, the speed of sound is approximately 343 m/s (1235 km/h).
Mach numbers are commonly used in aerospace engineering to describe the performance of aircraft, spacecraft, and projectiles. Understanding the Mach number is essential for predicting shock waves, aerodynamic drag, and thermal effects at high speeds.