Why is there a sonic boom at Mach 1.5?

  • Context: Undergrad 
  • Thread starter Thread starter Dead Rabit
  • Start date Start date
  • Tags Tags
    Mach
Click For Summary

Discussion Overview

The discussion centers around the phenomenon of sonic booms, particularly in relation to aircraft traveling at speeds greater than Mach 1.5. Participants explore the mechanics of sound wave generation, the nature of shock waves, and the implications of traveling at supersonic speeds.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant suggests that a sonic boom is an extreme form of the Doppler effect, questioning why sound generated at Mach 1.5 does not cancel itself out.
  • Another participant explains that at Mach 1, sound waves are no longer generated in the traditional sense, as the aircraft moves faster than the waves can form, creating a cone of high-pressure air instead.
  • A participant expresses interest in further reading on sonic booms, indicating a desire for deeper understanding of the topic.
  • One response mentions that shock waves form in various locations on the aircraft and that there are nested shock waves in the jet engine exhaust.
  • Another participant suggests searching for information on shock wave formation and NASA's supersonic aircraft for additional insights.
  • A later reply discusses how, at a distance from the aircraft, the air slows below sonic speed after the object passes, leading to a long-duration pulse rather than a sharp crack, and notes the occurrence of multiple booms from initial shock waves.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the nature of sonic booms and the mechanics behind them, with multiple competing views and explanations presented throughout the discussion.

Contextual Notes

Some claims about the nature of sound wave generation and shock waves remain unresolved, with participants expressing differing interpretations and assumptions about the physics involved.

Who May Find This Useful

This discussion may be of interest to those studying aerodynamics, sound wave physics, or anyone curious about the mechanics of supersonic flight and sonic booms.

Dead Rabit
It's my understanding that a sonic boom is the doppler effect taken to the extreme, with a sound emitting object traveling at the speed of sound, your building the ultimate constructive wave.

I want to know, if you were traveling at Mach 1.5, why doesn't the sound you're generating cancel itself out? (in layman's terms)

More precisely, if you understood how the frequency of the sound generated by your aircraft varied at different speeds as it's travelling, why can't you:
a) choose to travel at a speed that would destroy the sound wave produced?
b) deliberately place the elements of your design that cause drag (and hence, noise) offset by half the wavelength?

Or at least I assume you can't because it still takes 8 hours to fly to America from the UK, 50 years after Concorde was invented =P.

Cheers,
J
 
Physics news on Phys.org
Once you hit Mach 1, you're no longer generating sound waves in the traditional sense. Further increases in velocity do not create sound waves with different frequencies. What's happening is that you're pushing the air out of the way faster than it can form a wave in the first place. This creates a cone-shaped region of high-pressure air which expands outwards after the plane passes, which is where the sound comes from. Increasing the plane's velocity just elongates this cone.
 
  • Like
Likes   Reactions: phinds, CWatters and FactChecker
Interesting, are there any topics you can recommend I read up on to improve my understanding of this phenomenon?
"sonic boom" only seems to bring up high level synopsis.
 
Other than wikipedia, I'm afraid I can't. :cry:
 
The sonic boom is simply a moving shock wave. Shock waves form in many places on the wing and in the jet exhaust. In fact, in the jet engine exhaust, there is a nested set of shock waves, one inside the other. There is a great deal of information in books on aerodynamics. You can go to Amazon and find many books by searching "aerodynamics shock wave". I have never studied it, so I can not recommend any particular book.
 
Search on ' formation of shock waves on aircraft ' and ' NASA supersonic aircraft '
 
At a distance from the high speed object, the air will have slowed to below sonic speed. (i.e. When the object has passed) the impulse will have spread out and the particle speeds will no longer be sonic. What you hear is not a 'shock wave' but the remnants of it, spread out in time on the journey to the ground into a single pulse of long duration. Boom not crack.
You get more than one boom when there are multiple initial shock waves.
 
  • Like
Likes   Reactions: FactChecker

Similar threads

High School Why doesn't the Earth at the equator experience a sonic boom?
  • · Replies 53 ·
2
Replies
53
Views
9K
About Sonic Booms and Quiet Aircraft
  • · Replies 4 ·
Replies
4
Views
2K
Undergrad Interval between double sonic booms
  • · Replies 41 ·
2
Replies
41
Views
18K
Graduate Curiosity - Relative speeds in relation to the sound barrier?
  • · Replies 8 ·
Replies
8
Views
2K
Can we hear a supersonic plane?
  • · Replies 136 ·
5
Replies
136
Views
19K
Undergrad Is there such a thing as a photonic boom?
  • · Replies 1 ·
Replies
1
Views
3K
Undergrad Sonic Boom, Red Bull Stratos (possible?)
  • · Replies 42 ·
2
Replies
42
Views
8K
Calculating Altitude from Sonic Boom and Angle of Sight
  • · Replies 9 ·
Replies
9
Views
5K
Calculating Sonic Boom Time: Jet Aircraft at Mach 1.5 and Altitude of 5029m
  • · Replies 10 ·
Replies
10
Views
3K
Undergrad Why is there no sonic boom when shooting an air rifle at 1400 feet per second?
  • · Replies 30 ·
2
Replies
30
Views
33K