The Mach number is defined as the ratio of an object's speed to the speed of sound in the surrounding medium.

The Mach number is defined as the ratio of an object's speed to the speed of sound in the surrounding medium.

• A. True
• B. False
• C. It is the ratio of the object's speed to the speed of light
• D. It is the ratio of the medium's density to the speed of sound

Answer: (A)

Mach number is the ratio of how fast an object moves to the speed of sound in the surrounding medium. It’s defined as M = v / a, with v being the object's speed relative to the medium and a the local speed of sound in that medium. This makes the quantity dimensionless and dependent on the medium's properties, such as temperature and composition, since those factors set the speed of sound. That’s why the same physical speed can be subsonic in one medium and supersonic in another. For example, air at room temperature has a speed of sound around 343 m/s, so a plane traveling at 200 m/s has M ≈ 0.58, while the same plane in a medium where sound travels faster would have a different Mach number. The statement isn’t about the speed of light or any density ratio; those don’t define Mach.

Mach number is the ratio of how fast an object moves to the speed of sound in the surrounding medium. It’s defined as M = v / a, with v being the object's speed relative to the medium and a the local speed of sound in that medium. This makes the quantity dimensionless and dependent on the medium's properties, such as temperature and composition, since those factors set the speed of sound. That’s why the same physical speed can be subsonic in one medium and supersonic in another. For example, air at room temperature has a speed of sound around 343 m/s, so a plane traveling at 200 m/s has M ≈ 0.58, while the same plane in a medium where sound travels faster would have a different Mach number. The statement isn’t about the speed of light or any density ratio; those don’t define Mach.