Skip to content
Know.itKnow.it
Create an animated lesson
On request

This article is free to read. Creating a lesson uses your daily or stored credits; review the language and settings before starting.

How does a sonic boom happen?

ScienceLesson on requestFree to readयह पेज हिंदी में पढ़ें

Quick answer

A sonic boom occurs when an object moves through air faster than sound, compressing pressure waves into a shock front. This shock front forms a cone that sweeps across the ground, and when it passes a listener, the sudden pressure change is heard as a loud boom.

A sonic boom happens when an object travels through air faster than the speed of sound, creating a shock wave that reaches listeners as a loud crack. The boom is continuous while the object is supersonic, heard only when the shock wave sweeps past an observer.

Step by step

  1. An object moves through air, pushing air molecules aside and creating pressure waves that travel outward at the speed of sound.
  2. As the object approaches the speed of sound, the waves ahead bunch together, forming a dense wall of compressed air.
  3. When the object exceeds the speed of sound, it outruns the waves, and they combine into a single shock front.
  4. This shock front spreads out in a cone shape, with the object at the tip, known as the Mach cone.
  5. The cone's edge sweeps across the ground like a wake; when it reaches a listener, the sharp pressure jump is heard as a sonic boom.

Key things to understand

  1. Sound travels through air as pressure waves at about 343 metres per second (1,235 km/h) in air at 20 °C.
  2. An object moving faster than sound outruns the pressure waves it creates, piling them into a sharp shock front.
  3. This shock front is a cone-shaped wave that trails behind the object, called a Mach cone.
  4. When the cone's edge sweeps over a listener, the sudden pressure jump is heard as a sonic boom.
  5. The boom is not a one-time event; it follows the object and is heard wherever the cone passes.

Labelled diagram

  1. Subsonic

    Object moves slower than sound; pressure waves spread out ahead and behind.

  2. Transonic

    Object nears the speed of sound; waves pile up ahead, creating a barrier.

  3. Supersonic

    Object outruns waves; they merge into a single shock front.

  4. Mach cone

    Shock front forms a cone trailing the object, with the object at its tip.

  5. Boom heard

    Cone's edge sweeps over listener; sudden pressure change is heard as a boom.

How a sonic boom forms

Real-world examples

  • A military jet flying at supersonic speed over a desert produces a boom heard for kilometres along its path.
  • The Concorde, a retired supersonic airliner, created booms that led to bans on overland supersonic flights.
  • A bullwhip's crack is a small sonic boom caused by the tip briefly exceeding the speed of sound.
  • Spacecraft returning to Earth create sonic booms as they decelerate through the atmosphere.

Common mistake

✗ Myth: A sonic boom is a one-time explosion created only when an object breaks the sound barrier.

✓ Fact: The boom is continuous while the object flies supersonic, and it is heard only when the shock wave passes an observer. The 'barrier' is not a physical wall but a sharp rise in drag as waves pile up.

People also ask

What causes a sonic boom?
A sonic boom is caused by an object moving faster than the speed of sound. The object outruns its own pressure waves, which merge into a shock front. When this shock front sweeps past a listener, the sudden pressure change is heard as a boom.
Why is a sonic boom so loud?
A sonic boom is loud because the shock front is a very sharp pressure jump, much steeper than ordinary sound waves. This sudden change in pressure delivers a large amount of energy to the ear in a short time, making it sound like an explosion.
Can a sonic boom be heard from the ground?
Yes, a sonic boom can be heard on the ground if the shock cone intersects the surface. The boom is heard along a path called the boom carpet, which can be tens of kilometres wide, depending on the object's altitude and speed.
Can a sonic boom break windows?
Yes, a strong sonic boom can shatter windows and cause minor structural damage. The sharp pressure change rattles buildings, and repeated booms can weaken materials over time.
Why don't we hear sonic booms from passenger planes?
Most passenger planes cruise below the speed of sound, partly because supersonic flight burns far more fuel and partly because many countries ban civil supersonic flight over land to prevent noise and damage.
Is a sonic boom louder when the object is closer?
Generally yes, but loudness also depends on the object's size, shape, and speed, not just distance. A larger object creates a stronger shock wave, and lower altitude makes the boom louder on the ground.
Do sonic booms happen only in air?
No, they can occur in any medium where an object exceeds the local speed of sound. In water that threshold is about 1,500 metres per second, so such shock waves from moving objects are rare.

Part of the guide: Everyday Science: Light, Heat & Matter →