• Shalmali

Shock Waves and Sonic Boom!

Updated: Apr 23

What is the Mach Number?


Table of Contents:

  1. Introduction

  2. Velocity of Sound

  3. Mach Number

  4. Shock waves

  5. Sonic Boom

  6. Summary

  7. Short Video

Lazy Morning
Lazy Morning
It's a lazy Sunday. You are lying on your bed and chatting with your best friend.

But suddenly, out of nowhere, your mom appears in front of you! When did she come in? What a shock!!! This is something that happens with the sound waves too! Let's understand what and how shock waves are created. Before actually getting into Shock waves we need to understand a few basic terminologies, let's get into it first!


Shock Waves:


Velocity of Sound:


When we speak, we produce longitudinal waves, which create regions of compression and rarefaction alternatively. This is how sound travels, in compression and rarefaction alternate waves. The speed of sound is 340.29 m/s.


Mach Number:


Mach number is the ratio of inertial force to elastic force, when it is further deduced, it can be written as the ratio of object speed to speed of sound. The Mach Number is important because it tells us how the object will be affected by the presence of fluid in the surroundings.



Case 1: Subsonic (Mach No. < 1.0)


When Mach Number is less than 1, or when the speed of the object moving is less than the speed of sound, it is called a Subsonic condition.

Let's consider the same example that we were discussing before. Imagine you are sitting in your room and chilling out. You hear your mom's footsteps approaching your room. Mom opens the door, you wave her hi!

In this case, you were prepared that someone is approaching you as you heard the footsteps. On similar lines, you can imagine, when the sound waves travel slower than the moving object, the sound waves are prepared for the approaching object. The sound waves are expecting some object to pass through and the object arrives.


Case 2: Sonic (Mach No. = 1.0)


When Mach Number is equal to 1, or when the speed of the object moving is equal to the speed of sound, it is called as Sonic condition.

Again imagine the same example. You are sitting in your room and chilling out. But this time you could not hear your mom approaching you. Suddenly out of nowhere, you heard someone opening your room's door. Obviously, you were in a shock for few seconds, because you were not prepared for it.

Similarly, you can imagine, when the speed of the object is equal to the speed of sound, the sound waves are not ready for the object approaching. The sound waves had no idea that the object was entering its zone. Hence, the shock waves are created and these shock waves impact the object.


Case 3: Supersonic (Mach No. > 1.0)


When Mach Number is greater than 1, or when the speed of the object moving is greater than the speed of sound, it is called a Supersonic condition.

This time, you are sitting in your room and suddenly, someone is standing in from of you. That is a real terror, isn't it!

Similarly, if the object speed is greater than the speed of sound, greater shock waves and impact is created.


Case 4: Hypersonic (Mach No. > 5.0)


When Mach Number is greater than 5, or when the speed of the object moving is 5 times greater than the speed of sound, it is called a Hypersonic condition.


When the speed of object is greater than the speed of sound, impact force acts on the object, this is called as shock waves

The object can get damaged due to the high impact force. The greater the speed of the object, the greater is the impact on the object. The more the surface area of the object that enters the sound waves, the greater impact force acts on the object. Hence you might have seen the fighter planes have a very little surface (needle-like structure or very pointed nose) at the nose.


Sonic Boom:

Sonic boom is the sound that is produced during shock waves.

Sometimes, the sonic boom can be loud enough to cause minor damage to some structures. This sound travels as the object travels.


Conclusion:

  1. Mach number is the ratio of an object's speed to the speed of sound.

  2. There exist 3 cases: Subsonic, Sonic, and Hypersonic conditions, which depend on Mach Number.

  3. When the speed of an object is greater than the speed of sound, impact force acts on the object. These impact forces damage the objects.

  4. To reduce the impact force, the surface area should be reduced.

  5. A sonic boom is a sound that is produced during shock waves.

  • Mach Number < 1 ➡ Subsonic

  • Mach Number = 1 ➡ Sonic

  • Mach Number > 1 ➡ Supersonic / Hypersonic



How does this affect the fighter planes and what factors are considered in Hypersonic conditions? Want to know more about the topic in detail? Follow me for similar topics!


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