Artist: Yasutoki Kariya
日本设计师Yasutoki Kariya带来的灯泡版牛顿摇篮（Asobi），让我们感受一下思维火花的传递：
基本原理和牛顿摇篮类似，只不过以透明的灯泡取代了更常见的小球，它仍然能够演示出力的传递，让两边的灯泡在物理定律的作用交替弹起。不同的是，整个过程中，我们将看到灯泡的点亮与熄灭，它们将在弹开的瞬间完全点亮，闪烁出漂亮的光芒。或在传递过程中一闪即逝，清晰地标识出力的传递路线
http://player.youku.com/embed/XNDM3MDg5MTQ0
(I can’t embed the video on this post, so would have to click on the above URL link to access the YouKu video!)
Decided to pop by 8Q@SAM to visit and seek inspirations! It’s themed along the lines of “after image” as well, and have prove to be inspiring in its exhibitions.
http://www.singaporeartmuseum.sg/exhibitions/current.html
Fail to find out who the designer is
MUSIC
Harsh noise
(http://en.wikipedia.org/wiki/Noise_music)
Category of music that is characterised by the expressive use of noise within a musical context.
Challenge the distinction that is made in conventional musical practices between musical and non-musical sound.
It may incorporate live machine sounds, non-musical vocal techniques, physically manipulated audio media, processed sound recordings, field recording, computer generated noise, stochastic process and other randomly produced electronic signals such as distortion, feedback, static, hiss and hum. There may also be emphasis on high volume levels and lengthy, continuous pieces. More generally noise music may contain aspects such as improvisation, extended technique, cacophony and indeterminacy, and in many instances conventional use of melody, harmony, rhythm and pulse is often dispensed with.
ART
Art: Futurism
(http://en.wikipedia.org/wiki/Futurism)
Giacomo Balla, Abstract Speed + Sound, 1913–1914
Concept
Emphasized and glorified themes associated with contemporary concepts of the future, including speed, technology, youth and violence, and objects such as the car, the aeroplane and the industrial city.
Art: Dada
(http://en.wikipedia.org/wiki/Dada)
Hannah Höch, Cut with the Dada Kitchen Knife through the Last Weimar Beer-Belly Cultural Epoch in Germany, 1919, collage of pasted papers
Concept through words of Dona Budd’s The Language of Art Knowledge:
Dada was born out of negative reaction to the horrors of World War I. This international movement was begun by a group of artists and poets associated with the Cabaret Voltaire in Zurich. Dada rejected reason and logic, prizing nonsense, irrationality and intuition.
Art Technique: Marbling*
1. Ebru
Ebru is a traditional Islamic and Turkish painting art, and can be defined as painting on water and transferring this painting onto paper. This style is also called marbling.
A gum called tragacanth is added to the water to yield a thickened liquid, and horse hair brushes are used to apply paints which are insoluble in water.
2. Spray can marbling
Making use of the insolubility of spray can paint and water to crate patterns.
3. Paper marbling
French Curl paper by the late 20th-century French marbling master Michel Duval.
Method of aqueous surface design, which can produce patterns similar to smooth marble or other stone. The patterns are the result of color floated on either plain water or a viscous solution known as size, and then carefully transferred to an absorbent surface, such as paper or fabric.
Procedure – A shallow tray is filled with water, and various kinds of ink or paint colors are carefully applied to the surface with an ink brush. Various additives or surfactant chemicals are used to help float the colors. A drop of “negative” color made of plain water with the addition of surfactant is used to drive the drop of color into a ring. The process is repeated until the surface of the water is covered with concentric rings.
4. Japanese Marbling – Suminagashi
Suminagashi (墨 流 し) or “floating ink” is the process of marbling plain paper with water and ink to transform it into something vibrant and colorful. It originated in Japan as early as the 12th century.
The floating colors are then carefully manipulated either by blowing on them directly or through a straw, fanning the colors, or carefully using a human hair to stir the colors. In the 19th century, the Kyoto master Tokutaro Yagi developed a method for using a split piece of bamboo to gently stir the colors, resulting in concentric spiral designs. Finally, a sheet of washi paper is carefully laid onto the water surface to capture the floating design. The paper, which is often made of kozo (Paper Mulberry or Broussonetia papyrifera), must be unsized, and strong enough to withstand being immersed in water without tearing.
Various claims have been made regarding the origins of suminagashi. Some think that it may have originally come from China (Wolfe 6). Others have proposed that it may have derived from an early form of ink divination. Another theory is that the process may have derived from a form of popular entertainment at the time, in which a freshly painted sumi painting was immersed into water, and the ink slowly dispersed from the paper and rose to the surface, forming curious designs.
**On a side note, this is beautiful:
QUIET LUNCH MAGAZINE presents Holton x Dior ‘Pour Paintings’.
Art Technique: Wax
1. Batik
Technique of manual wax-resist dyeing applied to whole cloth, or cloth made using this technique. Batik is made either by drawing dots and lines of the resist with a spouted tool called a canting
**too much symbolism or cultural meaning to consider?
2. Encaustic painting (hot wax painting)
Involves using heated beeswax to which colored pigments are added. The liquid or paste is then applied to a surface—usually prepared wood, though canvas and other materials are often used. The simplest encaustic mixture can be made from adding pigments to beeswax, but there are several other recipes that can be used—some containing other types of waxes, damar resin, linseed oil, or other ingredients. Pure, powdered pigments can be used, though some mixtures use oil paints or other forms of pigment.
**too distant a culture? (Greek, etc.)
Solubility*
Property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent to form a homogeneous solution of the solute in the solvent. The solubility of a substance fundamentally depends on the physical and chemical properties of the solute and solvent as well as on temperature, pressure and the pH of the solution.
The extent of the solubility of a substance in a specific solvent is measured as the saturation concentration, where adding more solute does not increase the concentration of the solution and begin to precipitate the excess amount of solute.
Rayleigh-Taylor instability
http://en.wikipedia.org/wiki/Rayleigh–Taylor_instability
instability of an interface between two fluids of different densities which occurs when the lighter fluid is pushing the heavier fluid.
To model the last example, consider two completely plane-parallel layers of immiscible fluid, the more dense on top of the less dense one and both subject to the Earth’s gravity. The equilibrium here is unstable to any perturbations or disturbances of the interface: if a parcel of heavier fluid is displaced downward with an equal volume of lighter fluid displaced upwards, the potential energy of the configuration is lower than the initial state.
Hydrodynamics simulation of a single “finger” of the Rayleigh–Taylor instability. Note the formation of Kelvin–Helmholtz instabilities, in the second and later snapshots shown (starting initially around the level y = 0), as well as the formation of a “mushroom cap” at a later stage in the third and fourth frame in the sequence.
Kelvin-Helmholtz Instability
Occur when there is velocity shear in a single continuous fluid, or where there is a velocity difference across the interface between two fluids. An example is wind blowing over water: The instability manifests in waves on the water surface.
The theory predicts the onset of instability and transition to turbulent flow in fluids of different densities moving at various speeds. Helmholtz studied the dynamics of two fluids of different densities when a small disturbance, such as a wave, was introduced at the boundary connecting the fluids.
Richtmyer-Meshkov instability
http://en.wikipedia.org/wiki/Richtmyer–Meshkov_instability
When two fluids of different density are accelerated. Normally this is by the passage of a shock wave. The development of the instability begins with small amplitude perturbations which initially grow linearly with time. This is followed by a nonlinear regime with bubbles appearing in the case of a light fluid penetrating a heavy fluid, and with spikes appearing in the case of a heavy fluid penetrating a light fluid. A chaotic regime eventually is reached and the two fluids mix.
A three stage transition from a shock-accelerated layer with deterministic vortex-dominated growth, followed by a regime featuring both deterministic and stochastic growth of small-scale features, and ending with turbulent mixing of the layer with surrounding air.
Fluid thread breakup
Process by which a single mass of fluid breaks into several smaller fluid masses. The process is characterized by the elongation of the fluid mass forming thin, thread-like regions between larger nodules of fluid. The thread-like regions continue to thin until they break, forming individual droplets of fluid.
Thread breakup occurs where two fluids or a fluid in a vacuum form a free surface with surface energy. If more surface area is present than the minimum required to contain the volume of fluid, the system has an excess of surface energy. A system not at the minimum energy state will attempt to rearrange so as to move toward the lower energy state, leading to the breakup of the fluid into smaller masses to minimize the system surface energy by reducing the surface area. The exact outcome of the thread breakup process is dependent on the surface tension, viscosity, density, and diameter of the thread undergoing breakup.
The process undergone by a fluid thread or jet undergoing breakup from a larger mass to a smaller mass.
Radii of curvature in a thread undergoing the breakup process. Blue represents the first radius of curvature and red the second radius of curvature at the thinned and thickened locations.
Satellite drop formation
Drops produced during the thread breakup process in addition to the large main droplet. The drops result when the filament by which the main droplet in hanging from the larger fluid mass itself breaks off from the fluid mass.
Water flows from a faucet, producing both a single large droplet and several satellite droplets.
Water Repellent
Waterproofing is making an object virtually impervious to water. Waterproofing techniques have been implemented in several types of objects, going from different clothing products to paper packaging, cosmetics, and more recently, consumer electronics.
Hydrophobic
A droplet of water forms a spherical shape, minimizing contact with the hydrophobic leaf.
The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules, and they fall, specifically under the title rubric when a particular temperature dependence of the affinity of the apolar small molecule or moiety for the aqueous phase obtains. The part of the name, hydrophobic, literally meaning “water-fearing,” and it describes the segregation and apparent repulsion between water and nonpolar substances.
The origin of the hydrophobic effect is not fully understood. Some argue that the hydrophobic interaction is mostly an entropic effect originating from the disruption of highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute.
Superhydrophobic
Highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet exceeds 150° and the roll-off angle/contact angle hysteresis is less than 10°. This is also referred to as the Lotus effect, after the superhydrophobic leaves of the lotus plant.
Lotus
Lotus effect: Self-cleaning properties that are a result of very high water repellence (superhydrophobicity), as exhibited by the leaves of the lotus flower (Nelumbo)
Other plants: Tropaeolum (nasturtium), Opuntia (prickly pear), Alchemilla, cane, and also on the wings of certain insects
Due to their high surface tension, water droplets tend to minimize their surface by trying to achieve a spherical shape. On contact with a surface, adhesion forces result in wetting of the surface. Either complete or incomplete wetting may occur depending on the structure of the surface and the fluid tension of the droplet.
Wax
Class of chemical compounds that are plastic (malleable) near ambient temperatures. They are also a type of lipid.
Characteristically, they melt above 45 °C (113 °F) to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents. All waxes are organic compounds, both synthetic and naturally occurring.
All waxes are organic compounds, both synthetic and naturally occurring.
Uses:
Lava lamp
Decorative novelty item, invented by British accountant Edward Craven Walker in 1963, the founder of Mathmos. The lamp contains blobs of coloured wax inside a glass vessel filled with clear or translucent liquid; the wax rises and falls as its density changes due to heating from an incandescent light bulb underneath the vessel. The appearance of the wax is suggestive of pāhoehoe lava, hence the name. The lamps are designed in a variety of styles and colours.
Magic sand
Made from sand coated with a hydrophobic compound. The presence of this hydrophobic compound causes the grains of sand to adhere to one another and form cylinders (to minimize surface area) when exposed to water. When the sand is removed from water, it is completely dry and free flowing.
These properties are achieved with ordinary beach sand, which contains tiny particles of pure silica, and exposing it to vapors of trimethylsilanol (CH3)3SiOH, an organosilicon compound. Upon exposure, the trimethylsilane compound bonds to the silica particles while forming water. The exteriors of the sand grains are thus coated with hydrophobic groups.
CHEMISTRY
Chromatography
(/ˌkroʊməˈtɒɡrəfi/; from Greek χρῶμα chroma “color” and γράφειν graphein “to write”) is the collective term for a set of laboratory techniques for the separation of mixtures. The mixture is dissolved in a fluid called the mobile phase, which carries it through a structure holding another material called the stationary phase.
Chromatography may be preparative or analytical.
Types of Column Chromatography
Column chromatography is a separation technique in which the stationary bed is within a tube.
a. Traditional column chromatography
Column chromatography proceeds by a series of steps.
Method used to purify individual chemical compounds from mixtures of compounds. It is often used for preparative applications on scales from micrograms up to kilograms. The main advantage of column chromatography is the relatively low cost and disposability of the stationary phase used in the process. The latter prevents cross-contamination and stationary phase degradation due to recycling.
b. Flash column chromatography
Technique is very similar to the traditional column chromatography, except for that the solvent is driven through the column by applying positive pressure. This allowed most separations to be performed in less than 20 minutes, with improved separations compared to the old method
Types of Planar Chromatography
Separation technique in which the stationary phase is present as or on a plane. The plane can be a paper, serving as such or impregnated by a substance as the stationary bed (paper chromatography) or a layer of solid particles spread on a support such as a glass plate (thin layer chromatography).
Paper chromatography
Video of experiment:
Explaining theory:
Technique that involves placing a small dot or line of sample solution onto a strip of chromatography paper. The paper is placed in a container with a shallow layer of solvent and sealed. As the solvent rises through the paper, it meets the sample mixture, which starts to travel up the paper with the solvent. This paper is made of cellulose, a polar substance, and the compounds within the mixture travel farther if they are non-polar. More polar substances bond with the cellulose paper more quickly, and therefore do not travel as far.
Filter Paper
Filter paper is a semi-permeable paper barrier placed perpendicular to a liquid or air flow. It is used to separate fine solids from liquids or air.
Filter paper comes in various porosities and grades depending on the applications it is meant for. The important parameters are wet strength, porosity, particle retention, flow rate, compatibility, efficiency and capacity.
There are two mechanisms of filtration with paper; volume and surface. By volume filtration the particles are caught in the bulk of the filter paper. By surface filtration the particles are caught on the paper surface. Filter paper is mostly used because even a small piece of filter paper will absorb a significant volume of liquid
Others
i. Gas chromatography
Separation technique in which the mobile phase is a gas. Gas chromatographic separation is always carried out in a column, which is typically “packed” or “capillary”. Packed columns are the routine work horses of gas chromatography, being cheaper and easier to use and often giving adequate performance. Capillary columns generally give far superior resolution and although more expensive are becoming widely used, especially for complex mixtures. Both types of column are made from non-adsorbent and chemically inert materials. Stainless steel and glass are the usual materials for packed columns and quartz or fused silica for capillary columns.
ii. High performance liquid chromatography
Separation technique in which the mobile phase is a liquid. It can be carried out either in a column or a plane. Present day liquid chromatography that generally utilizes very small packing particles and a relatively high pressure is referred to as high performance liquid chromatography (HPLC).
iii. Chromatography in blood processing
Chromatographic techniques have been used in blood processing and purification since the 1980s. It has emerged as an effective method of purifying blood components for therapeutic use.
Blood plasma is the liquid component of blood, which contains dissolved proteins, nutrients, ions, and other soluble components. In whole blood, red blood cells, leukocytes, and platelets are suspended within the plasma. The goal of plasma purification and processing is to extract specific materials that are present in blood, and use them for restoration and repair. There are several components that make up blood plasma, one of which is the protein albumin. Albumin is a highly water-soluble protein with considerable structural stability. It serves as a transportation device for materials such as hormones, enzymes, fatty acids, metal ions, and medicinal products. It is also used for therapeutic purposes, being essential in restoration and maintenance of circulating blood volume in imperative situations such as severe trauma or surgery. With little room for error, extremely pure samples that are lacking impurities needs to be at hand in good amount.
Centrifugal force
(from Latin centrum, meaning “center“, and fugere, meaning “to flee”[1][2]) is the apparent force that draws a rotating body away from the center of rotation. It is caused by the inertia of the body. In Newtonian mechanics, the term centrifugal force is used to refer to one of two distinct concepts: an inertial force (also called a “fictitious” force) observed in a non-inertial reference frame, and also the equal and opposite reaction to a centripetal force.
Demonstration:
Difference between centrifugal and centripetal
Centrifugal force is most commonly introduced as an outward force apparent in a rotating frame of reference. It is apparent (fictitious) in the sense that it is not part of an interaction but is a result of rotation — with no reaction-force counterpart. This type of force is associated with describing motion in a non-inertial reference frame, and referred to as a fictitious or inertial force (a description that must be understood as a technical usage of these words that means only that the force is not present in a stationary or inertial frame)
State of matter
Evaporation is a type of vaporization of a liquid that occurs from the surface of a liquid into a gaseous phase that is not saturated with the evaporating substance. The other type of vaporization is boiling, which is characterized by bubbles of saturated vapor forming in the liquid phase. Steam produced in a boiler is another example of evaporation occurring in a saturated vapor phase. Evaporation that occurs directly from the solid phase below the melting point, as commonly observed with ice at or below freezing or moth crystals (napthalene or paradichlorobenzine), is called sublimation.
For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces. With sufficient temperature, the liquid would turn into vapor quickly (see boiling point). When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with enough energy to ‘escape’.
Kinetic Theory
Describes a gas as a large number of small particles (atoms or molecules), all of which are in constant, random motion. The rapidly moving particles constantly collide with each other and with the walls of the container. Kinetic theory explains macroscopic properties of gases, such as pressure, temperature, viscosity, thermal conductivity, and volume, by considering their molecular composition and motion. The theory posits that gas pressure is due to the impacts, on the walls of a container, of molecules or atoms moving at different velocities. Except during collisions, the interactions among molecules are negligible. (That is, they exert no forces on one another.
Brownian motion
(http://en.wikipedia.org/wiki/Brownian_motion)
Random motion of particles suspended in a fluid (a liquid or a gas) resulting from their collision with the quick atoms or molecules in the gas or liquid. The term “Brownian motion” can also refer to the mathematical model used to describe such random movements, which is often called a particle theory.
This is a simulation of the Brownian motion of a big particle (dust particle) that collides with a large set of smaller particles (molecules of a gas) which move with different velocities in different random directions.
Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors.
Occurs both in liquid and gaseous state
Collision theory
(http://www.chemguide.co.uk/physical/basicrates/introduction.html)
Explains how chemical reactions occur and why reaction rates differ for different reactions. The collision theory states that when suitable particles of the reactant hit each other, only a certain percentage of the collisions cause any noticeable or significant chemical change; these successful changes are called successful collisions. The successful collisions have enough energy, also known as activation energy, at the moment of impact to break the preexisting bonds and form all new bonds. This results in the products of the reaction. Increasing the concentration of the reactant particles or raising the temperature, thus bringing about more collisions and therefore many more successful collisions, increases the rate of reaction.
Reaction rate tends to increase with concentration phenomenon explained by collision theory.
The orientation of collision
Consider a simple reaction involving a collision between two molecules – ethene, CH2=CH2, and hydrogen chloride, HCl, for example. These react to give chloroethane.
As a result of the collision between the two molecules, the double bond between the two carbons is converted into a single bond. A hydrogen atom gets attached to one of the carbons and a chlorine atom to the other.
The reaction can only happen if the hydrogen end of the H-Cl bond approaches the carbon-carbon double bond. Any other collision between the two molecules doesn’t work. The two simply bounce off each other.
The double bond has a high concentration of negative charge around it due to the electrons in the bonds. The approaching chlorine atom is also slightly negative because it is more electronegative than hydrogen. The repulsion simply causes the molecules to bounce off each other.
PHYSICS
Inertia
Resistance of any physical object to any change in its state of motion, including changes to its speed and direction. It is the tendency of objects to keep moving in a straight line at constant velocity.
Inertia is one of the primary manifestations of mass, which is a quantitative property of physical systems. Isaac Newton defined inertia as his first law in his Philosophiæ Naturalis Principia Mathematica, which states:
The vis insita, or innate force of matter, is a power of resisting by which every body, as much as in it lies, endeavours to preserve its present state, whether it be of rest or of moving uniformly forward in a straight line.
Magnetic Levitation
Magnetic levitation, maglev, or magnetic suspension is a method by which an object is suspended with no support other than magnetic fields. Magnetic force is used to counteract the effects of the gravitational and any other accelerations.
The two primary issues involved in magnetic levitation are lifting force: providing an upward force sufficient to counteract gravity, and stability: insuring that the system does not spontaneously slide or flip into a configuration where the lift is neutralized.
Making own levitating top:
** Unstable stability, easily affected by humidity, temperature and external environment
Lift
Magnetic materials and systems are able to attract or press each other apart or together with a force dependent on the magnetic field and the area of the magnets, For example, the simplest example of lift would be a simple dipole magnet positioned in the magnetic field of another dipole magnet, oriented with like poles facing each other, so that the force between magnets repels the two magnets.
Stability
Earnshaw’s theorem proves that using only paramagnetic materials (such as ferromagnetic iron) it is impossible for a static system to stably levitate against gravity.
For example, the simplest example of lift with two simple dipole magnets repelling is highly unstable, since the top magnet can slide sideways, or flip over, and it turns out that no configuration produced adding more magnets can produce stability.
However, servomechanisms, the use of diamagnetic materials, superconduction, or systems involving eddy currents allow stability to be achieved.
In some cases the lifting force is provided by magnetic levitation, but stability is provided by a mechanical support bearing little load. This is termed pseudo-levitation.
Superconductivity
Transition from ordinary conductivity (left) to superconductivity (right). At the transition, the superconductor expels the magnetic field and then acts as a perfect diamagnet.
Phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.
The interior of a bulk superconductor cannot be penetrated by a weak magnetic field, a phenomenon known as the Meissner effect. When the applied magnetic field becomes too large, superconductivity breaks down.
Type-I superconductors
Superconductivity is abruptly destroyed via a first order phase transition when the strength of the applied field rises above a critical value Hc. This type of superconductivity is normally exhibited by pure metals, e.g. aluminium, lead, and mercury. Depending on the demagnetization factor, one may obtain an intermediate state. This state, first described by Lev Landau, is a phase separation into macroscopic non-superconducting and superconducting domains.
Type-II superconductor
Characterized by the formation of magnetic vortices in an applied magnetic field. This occurs above a certain critical field strength Hc1. The vortex density increases with increasing field strength. At a higher critical field Hc2, superconductivity is completely destroyed.
Meissner effect
When a superconductor is placed in a weak external magnetic field H, and cooled below its transition temperature, the magnetic field is ejected. The Meissner effect does not cause the field to be completely ejected but instead the field penetrates the superconductor but only to a very small distance, characterized by a parameter λ, called the London penetration depth, decaying exponentially to zero within the bulk of the material. The Meissner effect is a defining characteristic of superconductivity. For most superconductors, the London penetration depth is on the order of 100 nm.
Diamagnetism
Diamagnetism appears in all materials, and is the tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field. However, in a material with paramagnetic properties (that is, with a tendency to enhance an external magnetic field), the paramagnetic behavior dominates. Diamagnetic materials create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are repelled by the applied magnetic field.
Unlike a ferromagnet, a diamagnet is not a permanent magnet. Its magnetic permeability is less than μ0 (the permeability of free space). In most materials diamagnetism is a weak effect, but a superconductor repels the magnetic field entirely, apart from a thin layer at the surface.
Acoustic levitation
Method for suspending matter in a medium by using acoustic radiation pressure from intense sound waves in the medium.
Electrostatic Leviation
Process of using an electric field to levitate a charged object and counteract the effects of gravity. It was used, for instance, in Robert Millikan‘s oil drop experiment and is used to suspend the gyroscopes in Gravity Probe B during launch.
Due to Earnshaw’s theorem no static arrangement of classical electrostatic fields can be used to stably levitate a point charge. There is an equilibrium point where the two fields cancel, but it is an unstable equilibrium.
Shockwave
Type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or in some cases in the absence of a material medium, through a field such as an electromagnetic field. Shock waves are characterized by an abrupt, nearly discontinuous change in the characteristics of the medium.
Shock waves are not conventional sound waves; a shock wave takes the form of a very sharp change in the gas properties on the order of a few mean free paths (roughly micrometers at atmospheric conditions) in thickness. Shock waves in air are heard as a loud “crack” or “snap” noise. Over longer distances a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy. The sound wave is heard as the familiar “thud” or “thump” of a sonic boom, commonly created by the supersonic flight of aircraft.
Pei Yun's Process Journal 