Tyler Wynn
Shockwaves are not conventional sound waves. They are created when an object travels faster than the speed of sound, causing a sudden and violent change in pressure, temperature, and density. This can be achieved by supersonic aircraft, explosions, or other phenomena. Shockwaves can also occur in water or solid substances, and they are of interest in medicine, where they are used in treatments such as low-intensity Extracorporeal Shockwave Therapy (Li-ESWT). This raises the question: are shockwaves only created by sound, or are there other factors at play?
| Characteristics | Values |
|---|---|
| Definition | A shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a given medium (such as air, water or a solid substance). |
| Difference from sound waves | Unlike sound waves, shock waves are characterised by an abrupt, nearly discontinuous change in pressure, temperature and density of the medium. |
| Formation | Shock waves are formed when an object moves at a speed equal to or faster than the speed of sound, causing a sudden rise and fall of air pressure. |
| Visibility | Shock waves are visible due to the sudden decrease in air pressure, which causes water molecules in the air to condense. |
| Examples | Shock waves can be created by supersonic aircraft, explosions, lightning or other phenomena that create violent changes in pressure. |
| Medical Applications | Radial pressure wave devices that generate ballistic radial pressure waves are used for the treatment of erectile dysfunction. |
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What You'll Learn
Shockwaves are not conventional sound waves
In physics, a shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a given medium (such as air or water). Shock waves are not conventional sound waves. While sound waves can be thought of as the propagation of compression followed by relaxation of particles of a medium, shock waves are characterized by an abrupt, nearly discontinuous change in pressure, temperature, and density of the medium. This abrupt change in pressure is what distinguishes shock waves from sound waves, as the latter does not exhibit such sudden changes.
Shock waves are often created by supersonic aircraft, explosions, or other phenomena that generate violent changes in pressure. For example, when an aircraft travels faster than the speed of sound, it creates a shock wave just ahead of its wing's leading edge. This shock wave then moves to the trailing edge of the wing, with the higher pressure behind it and lower pressure ahead, resulting in a force that lifts and pushes the wing up and back. The formation of shock waves around aircraft is what led to the concept of a ""sound barrier," which was first broken in 1947 by the Bell X-1 aircraft.
The presence of a shock wave can be heard as a loud "crack" or "snap" noise. Over longer distances, a shock wave can degenerate into a conventional sound wave as it loses energy and heats the air around it. This results in the familiar "thud" or "thump" of a sonic boom, commonly associated with supersonic aircraft. However, it is important to distinguish between the shock wave and the sonic boom, as they are different phenomena.
While shock waves are not conventional sound waves, there is a theory that describes shock waves as a superposition of regular sound waves. According to this theory, when an object, such as an aircraft, travels faster than sound, the wavefronts can interfere constructively to form a shock wave. This is different from ordinary sound waves, which do not exhibit such constructive interference. Additionally, the intensity of a shock wave decreases faster than that of a sound wave due to the energy expenditure required to heat the medium through which it travels.
In medicine, the term "shockwave" is used to describe certain types of treatment modalities, such as Low-intensity Extracorporeal Shockwave Therapy (Li-ESWT), which is used for treating erectile dysfunction. However, these "shockwaves" are more similar to ordinary sound waves in terms of their lower peak pressure, slower rise time, and propagation without a focal point.
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Shockwaves are created by explosions
In physics, a shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a given medium (such as air or water). Shock waves are not conventional sound waves; they take the form of a very sharp change in the gas properties of the medium. While shock waves can be created by supersonic aircraft, explosions, lightning, or other phenomena that create violent changes in pressure, this article will focus on shock waves created by explosions.
Explosions, such as those caused by high explosives like TNT or nuclear bombs, can generate shock waves that travel at supersonic velocity from their point of origin. These shock waves are curved and form a small distance in front of the body of the explosion. Directly in front of the explosion, they stand at 90 degrees to the oncoming flow and then curve around it. The rules governing the shock wave's distance ahead of the explosion are complicated and depend on the shape of the explosive device.
The amplitude of a strong shock wave created by an explosion decreases almost as the inverse square of the distance until it becomes so weak that it obeys the laws of acoustic waves. Shock waves can alter the mechanical, electrical, and thermal properties of solids, making them useful in studying the equation of state (the relation between pressure, temperature, and volume) of any material.
Blast waves, which are a type of shock wave, are characterized by an increased pressure and flow resulting from the deposition of a large amount of energy in a small, localized volume. They have a leading shock front of compressed gases, followed by a blast wind of negative gauge pressure that pulls items back towards the center of the explosion. The original explosion sends out fragments that travel very fast, and the blast wind can cause more injuries by sweeping up debris and even people.
In conclusion, shock waves are not solely created by sound but can also be generated by explosions, among other phenomena. Explosions can create powerful shock waves that travel at supersonic speeds and have various effects, including damaging surrounding areas and injuring people through blast winds, debris, and fires.
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Shockwaves are formed by aircraft
In physics, a shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a given medium, such as air or water. Shock waves are not conventional sound waves; they are characterised by an abrupt, nearly discontinuous change in pressure, temperature, and density of the medium. They differ from sound waves in that the wavefront, where compression occurs, is a region of sudden and violent change in stress, density, and temperature.
Shock waves can be created by supersonic aircraft, explosions, lightning, or other phenomena that cause violent changes in pressure. When an aircraft travels at high subsonic speed, regions of air around it may be moving at the speed of sound, causing the sound waves leaving the aircraft to pile up on one another. As the aircraft approaches the speed of sound, it catches up to its own pressure waves, and the air ahead of it has no warning of the plane's approach. The aircraft then plows through the air, creating a shock wave. The airflow behind the shock wave becomes turbulent, increasing drag.
The formation and strength of shock waves can be influenced by the design of the aircraft. Thin wings help delay the formation and reduce the strength of shock waves, while sweeping the wings back makes them seem thinner to the airstream. High-speed wings perform well at low speeds, but some aircraft compensate for their lack of lift at low speeds by using flaps and other devices.
Shock waves in air are heard as a loud "crack" or "snap" noise. Over longer distances, a shock wave can degenerate into a conventional sound wave as it loses energy, creating the familiar "thud" or "thump" of a sonic boom. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference.
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Shockwaves are caused by lightning
A shock wave is a type of propagating disturbance that moves faster than the local speed of sound in a given medium, such as air, water, or a solid substance. It is characterised by an abrupt change in pressure, temperature, and density of the medium. While shock waves are often created by supersonic aircraft, explosions, or other phenomena, they can also be caused by lightning.
Lightning is a natural electrical discharge that occurs between clouds or between a cloud and the ground. When lightning occurs, it creates a channel of superheated plasma, which rapidly expands and collides with the surrounding cooler air. This collision results in a sudden and violent change in pressure, temperature, and density, leading to the formation of a shock wave.
The shock wave produced by lightning is commonly referred to as thunder. It is accompanied by a loud cracking or snapping sound, followed by continuous rumbling. The sound pressure level of thunder can reach up to 165 to 180 dB, and in some cases, even exceed 200 dB. This is due to the intense energy released during the generation of thunder.
The shock wave generated by lightning can have significant impacts. It is capable of causing property damage and injuries, such as internal contusions, chest and lung damage, bone fractures, and rupture of internal organs. The risk of injury depends on various factors, including the distance from the lightning strike and the presence of protective gear.
In summary, shockwaves are not solely created by sound. They can also be a result of lightning strikes, which lead to abrupt changes in pressure, temperature, and density, thus forming shock waves that propagate through the medium at supersonic speeds. Understanding the nature of shock waves caused by lightning is crucial for assessing and mitigating the potential risks associated with this natural phenomenon.
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Shockwaves can be used in medicine
Shockwaves have many applications in medicine. They were originally used to break up kidney stones, but now they are used in orthopaedic pain therapy, to treat patients with Alzheimer's disease, and in erectile dysfunction treatments, among other things.
To understand the range of applications, it is worth considering the physical properties of shock waves. Shock waves are not conventional sound waves; they are created by a sharp change in gas properties and travel faster than the speed of sound. When a shock wave meets a borderline between two tissues, it may be transmitted, dissipated, or reflected. In the human body, the kinetic energy carried by the wave is absorbed according to the structure of the tissues exposed. Shockwaves can pass through many types of tissue without causing damage, and their ability to fraction and disintegrate calcified stones and nodules is one of the basic clinical applications of shockwave therapy (SWT).
The different types of shockwave therapy include intra- and extracorporeal treatments. The most common are focused shockwave therapy (f SWT), radial shockwave therapy (r SWT), and planar shock wave therapy (p SWT). Radial pressure waves are generated by a controlled explosion, leading to an acceleration of a projectile into a probe, creating a wave. These are more like "ordinary" sound waves as they achieve a lower peak pressure and slower rise time.
Shockwaves are also used in ultrasonography, where the reflected ultrasound waves are recorded by transducers and translated into an image.
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Frequently asked questions
A shockwave is a strong pressure wave in any elastic medium such as air, water, or a solid substance. It is produced by supersonic aircraft, explosions, lightning, or other phenomena that create violent changes in pressure.
Shockwaves are formed when an object moves at the speed of sound or faster, creating a sudden rise and fall in air pressure.
Shockwaves differ from sound waves in that they travel faster than the speed of sound and their speed increases as the amplitude is raised. They also alter the mechanical, electrical, and thermal properties of solids.
Yes, shockwaves can be created without sound. For example, shockwaves can be created by high explosives such as TNT, lightning, or supersonic aircraft.
