Shock wave

A shock wave (English shockwave ), also pop wave in fluid dynamics a strong pressure wave that is generated by explosions and other phenomena that cause extreme pressure differences. The pressure wave travels here as wavefront through the medium.

Origin and basic properties of shock waves

In compressible, ie compressible media such as gases, spread disturbances caused about by moving through solids pressure changes, through the medium as pressure waves that travel at the speed of sound of the medium. The interferer moves slowly compared to the speed of sound, it allows the pressure wave to the medium to spread new, to compensate for the disturbance. The medium behaves like an incompressible medium.

The interferer moving but faster than the speed of sound in the undisturbed medium, a thin shock front, within which almost abruptly change the state variables of the medium, including the speed is. The front moves slowly through the medium as the interferer, so tapered shapes. Since the energy density behind the front is higher than before the front, shock waves sound gradually decreases to normal pressure waves, their speed is reduced to the speed of sound.

There are two basic types of shock waves that are equivalent but physically and differ only by the choice of the reference system:

Examples

Progressive shock waves

• Detonations, such as bombs, are able to leave with their shockwaves objects flying through the air and destroy. For such detonation waves exist exact empirical and theoretical calculation models. A pyrotechnic composition does not form a shock wave from, he also does not detonate, therefore, we speak of ( fast ) burn or deflagration.
• Aircraft flying at supersonic speeds, causing a conical shock wave, the Mach cone. Also in the atmosphere penetrating meteoroids cause shock waves, which are responsible for the light appearance of the meteors.
• The around the lightning channel strongly heated air caused by the plasma from him ( a few meters ) outgoing shock wave the Thunderclap during thunderstorms. So it is a kind of explosion along the lightning channel. Due to the irregular, often highly branched form of the lightning channel, the different distance of the lightning channel sections to the observer, as well as atmospheric temperature fluctuations and strong winds, which influence the course of the waves, not a single blow but mostly a whole series sounds more or less severe blows that form the typical growl or rumble of thunder - at a greater distance - where the shock waves have subsided to acoustic waves.
• In the interstellar medium shock waves ( eg, a dwarf galaxy ) are caused in a gas-rich galaxy like the Milky Way and through the compression of gas and dust clouds of star formation by supernovae or by ingress of gas and dust clouds. Undetectable they are also the basis of the broadcast from shock heated medium X-rays.
• The bow wave of ships sailing faster than its hull speed, a shock wave.
• According produce electrically charged particles moving in optical media faster than the speed of light in force there ( phase velocity ) move ( it is, for example, in water only 230,000 km / s), an electromagnetic bow wave, the Cherenkov radiation.

Standing shock waves

• The boundary of the magnetosphere of the Earth is characterized by a shock wave at the front, the particles of the solar wind is decelerated abruptly. Since the average velocity of the particles in the undisturbed flow to the ground is relatively larger than the speed of sound within the moving medium, it comes to the shock wave formation.
• In about 50-100 AU, the solar wind is decelerated by the interstellar medium. At the border, the termination shock, a shock wave can occur.
• In rocket engines, shock waves can occur which can lead to the destruction of the rocket faulty configuration. Since shock waves are to be avoided, the maximum ejection velocity and thereby the thrust is limited.

Application in medicine and physiotherapy

These shock waves are generated outside the body, so they are called extracorporeal. They can be hydraulic, electromagnetic, piezoelectric or pneumatic- ballistic generated. A distinction is made according to the shape of their propagation between radial and focused shock waves of different energies.

In medicine, high-energy focused shock waves in the ESWL ( Extracorporeal shock wave lithotripsy ) are used for fragmentation of urinary, biliary, kidney and salivary stones.

High-energy shock waves (ESWT ) one uses in orthopedics for the treatment of non-healing bone fractures ( non-unions ) and the erosion of calcifications of tendons and deposits in joints.

Low-energy shock waves enable effective treatment of pain in tendons such as tennis elbow, golfer's elbow and painful heel spurs and pain in osteoarthritis ( wear and tear disease) and chronic pain near the bone soft tissue.

Increasingly, sets the shock wave as pain free traveling of the so-called trigger point therapy of muscle tightness through. The trigger points ( = myogeloses ) of the muscle to be treated with neck pain and lower back pain, for example. The devices not only the treatment can be carried out, but they also allow a specific diagnosis of the hardened and condensed, usually often very painful muscle areas. These muscle areas are provided, depending on the disease with local or remote triggers that must be observed in the course of further treatment.

Due to its relative ease of use ( no imaging procedures necessary little risk, little pain for the patient ) is in particular the low-energy radial shock wave therapy in recent times more and more use in physiotherapy.