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Acoustics

Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics technology may be called an acoustical engineer. The application of acoustics is present in almost all aspects of modern society with the most obvious being the audio and noise control industries.

Hearing is one of the most crucial means of survival in the animal world and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as a key element of mating rituals or for marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay's "Wheel of Acoustics" is a well accepted overview of the various fields in acoustics.

Etymology
The word "acoustic" is derived from the Greek word ἀκουστικός (akoustikos), meaning "of or for hearing, ready to hear" and that from ἀκουστός (akoustos), "heard, audible", which in turn derives from the verb ἀκούω(akouo), "I hear".

The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics and later a branch of acoustics. Frequencies above and below the audible range are called "ultrasonic" and "infrasonic", respectively.

Early research in acoustics

In the 6th century BC, the ancient Greek philosopher Pythagoras wanted to know why some combinations of musical sounds seemed more beautiful than others, and he found answers in terms of numerical ratios representing the harmonic overtone series on a string. He is reputed to have observed that when the lengths of vibrating strings are expressible as ratios of integers (e.g. 2 to 3, 3 to 4), the tones produced will be harmonious, and the smaller the integers the more harmonious the sounds. For example, a string of a certain length would sound particularly harmonious with a string of twice the length (other factors being equal). In modern parlance, if a string sounds the note C when plucked, a string twice as long will sound a C an octave lower. In one system of musical tuning, the tones in between are then given by 16:9 for D, 8:5 for E, 3:2 for F, 4:3 for G, 6:5 for A, and 16:15 for B, in ascending order.

Aristotle (384–322 BC) understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air which is next to it...", a very good expression of the nature of wave motion. On Things Heard, generally ascribed to Strato of Lampsacus, states that the pitch is related to the frequency of vibrations of the air and to the speed of sound.

In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters including discussion of interference, echoes, and reverberation—the beginnings of architectural acoustics. In Book V of his De architectura (The Ten Books of Architecture) Vitruvius describes sound as a wave comparable to a water wave extended to three dimensions, which, when interrupted by obstructions, would flow back and break up following waves. He described the ascending seats in ancient theaters as designed to prevent this deterioration of sound and also recommended bronze vessels of appropriate sizes be placed in theaters to resonate with the fourth, fifth and so on, up to the double octave, in order to resonate with the more desirable, harmonious notes.

During the Islamic golden age, Abū Rayhān al-Bīrūnī (973-1048) is believed to have postulated that the speed of sound was much slower than the speed of light.

The physical understanding of acoustical processes advanced rapidly during and after the Scientific Revolution. Mainly Galileo Galilei (1564–1642) but also Marin Mersenne (1588–1648), independently, discovered the complete laws of vibrating strings (completing what Pythagoras and Pythagoreans had started 2000 years earlier). Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread through the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of the speed of sound in air were carried out successfully between 1630 and 1680 by a number of investigators, prominently Mersenne. Meanwhile, Newton (1642–1727) derived the relationship for wave velocity in solids, a cornerstone of physical acoustics (Principia, 1687).

Age of Enlightenment and onward
Substantial progress in acoustics, resting on firmer mathematical and physical concepts, was made during the eighteenth century by Euler (1707–1783), Lagrange (1736–1813), and d'Alembert (1717–1783). During this era, continuum physics, or field theory, began to receive a definite mathematical structure. The wave equation emerged in a number of contexts, including the propagation of sound in air.

In the nineteenth century the major figures of mathematical acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, and Lord Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work The Theory of Sound (1877). Also in the 19th century, Wheatstone, Ohm, and Henry developed the analogy between electricity and acoustics.

The twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge that was by then in place. The first such application was Sabine's groundbreaking work in architectural acoustics, and many others followed. Underwater acoustics was used for detecting submarines in the first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing. The ultrasonic frequency range enabled wholly new kinds of application in medicine and industry. New kinds of transducers (generators and receivers of acoustic energy) were invented and put to use.

Definition
Acoustics is defined by ANSI/ASA S1.1-2013 as "(a) Science of sound, including its production, transmission, and effects, including biological and psychological effects. (b) Those qualities of a room that, together, determine its character with respect to auditory effects."

The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations.

 * Cause-effect diagram for acoustics.svg

The steps shown in the above diagram can be found in any acoustical event or process. There are many kinds of cause, both natural and volitional. There are many kinds of transduction process that convert energy from some other form into sonic energy, producing a sound wave. There is one fundamental equation that describes sound wave propagation, the acoustic wave equation, but the phenomena that emerge from it are varied and often complex. The wave carries energy throughout the propagating medium. Eventually this energy is transduced again into other forms, in ways that again may be natural and/or volitionally contrived. The final effect may be purely physical or it may reach far into the biological or volitional domains. The five basic steps are found equally well whether we are talking about an earthquake, a submarine using sonar to locate its foe, or a band playing in a rock concert.

The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids, sound propagates primarily as a pressure wave. In solids, mechanical waves can take many forms including longitudinal waves, transverse waves and surface waves.

Acoustics looks first at the pressure levels and frequencies in the sound wave and how the wave interacts with the environment. This interaction can be described as either a diffraction, interference or a reflection or a mix of the three. If several media are present, a refraction can also occur. Transduction processes are also of special importance to acoustics.

Wave propagation: pressure levels
In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. While this disturbance is usually small, it is still noticeable to the human ear. The smallest sound that a person can hear, known as the threshold of hearing, is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is related to the sound pressure level (SPL) which is measured on a logarithmic scale in decibels.

Wave propagation: frequency
Physicists and acoustic engineers tend to discuss sound pressure levels in terms of frequencies, partly because this is how our ears interpret sound. What we experience as "higher pitched" or "lower pitched" sounds are pressure vibrations having a higher or lower number of cycles per second. In a common technique of acoustic measurement, acoustic signals are sampled in time, and then presented in more meaningful forms such as octave bands or time frequency plots. Both of these popular methods are used to analyze sound and better understand the acoustic phenomenon.

The entire spectrum can be divided into three sections: audio, ultrasonic, and infrasonic. The audio range falls between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has a number of applications, including speech communication and music. The ultrasonic range refers to the very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths which allow better resolution in imaging technologies. Medical applications such as ultrasonography and elastography rely on the ultrasonic frequency range. On the other end of the spectrum, the lowest frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomena such as earthquakes.

Analytic instruments such as the spectrum analyzer facilitate visualization and measurement of acoustic signals and their properties. The spectrogram produced by such an instrument is a graphical display of the time varying pressure level and frequency profiles which give a specific acoustic signal its defining character.

Transduction in acoustics
A transducer is a device for converting one form of energy into another. In an electroacoustic context, this means converting sound energy into electrical energy (or vice versa). Electroacoustic transducers include loudspeakers, microphones, particle velocity sensors, hydrophones and sonar projectors. These devices convert a sound wave to or from an electric signal. The most widely used transduction principles are electromagnetism, electrostatics and piezoelectricity.

The transducers in most common loudspeakers (e.g. woofers and tweeters), are electromagnetic devices that generate waves using a suspended diaphragm driven by an electromagnetic voice coil, sending off pressure waves. Electret microphones and condenser microphones employ electrostatics—as the sound wave strikes the microphone's diaphragm, it moves and induces a voltage change. The ultrasonic systems used in medical ultrasonography employ piezoelectric transducers. These are made from special ceramics in which mechanical vibrations and electrical fields are interlinked through a property of the material itself.

Acoustician
An acoustician is an expert in the science of sound.

Education
There are many types of acoustician, but they usually have a Bachelor's degree or higher qualification. Some possess a degree in acoustics, while others enter the discipline via studies in fields such as physics or engineering. Much work in acoustics requires a good grounding in Mathematics and science. Many acoustic scientists work in research and development. Some conduct basic research to advance our knowledge of the perception (e.g. hearing, psychoacoustics or neurophysiology) of speech, music and noise. Other acoustic scientists advance understanding of how sound is affected as it moves through environments, e.g. underwater acoustics, architectural acoustics or structural acoustics. Other areas of work are listed under subdisciplines below. Acoustic scientists work in government, university and private industry laboratories. Many go on to work in Acoustical Engineering. Some positions, such as Faculty (academic staff) require a Doctor of Philosophy.

Archaeoacoustics
Archaeoacoustics, also known as the archaeology of sound, is one of the only ways to experience the past with senses other than our eyes. Archaeoacoustics is studied by testing the acoustic properties of prehistoric sites, including caves. Iegor Rezkinoff, a sound archaeologist, studies the acoustic properties of caves through natural sounds like humming and whistling. Archaeological theories of acoustics are focused around ritualistic purposes as well as a way of echolocation in the caves. In archaeology, acoustic sounds and rituals directly correlate as specific sounds were meant to bring ritual participants closer to a spiritual awakening. Parallels can also be drawn between cave wall paintings and the acoustic properties of the cave; they are both dynamic. Because archaeoacoustics is a fairly new archaeological subject, acoustic sound is still being tested in these prehistoric sites today.

Aeroacoustics
Aeroacoustics is the study of noise generated by air movement, for instance via turbulence, and the movement of sound through the fluid air. This knowledge is applied in acoustical engineering to study how to quieten aircraft. Aeroacoustics is important for understanding how wind musical instruments work.

Acoustic signal processing
Acoustic signal processing is the electronic manipulation of acoustic signals. Applications include: active noise control; design for hearing aids or cochlear implants; echo cancellation; music information retrieval, and perceptual coding (e.g. MP3 or Opus).

Architectural acoustics

Architectural acoustics (also known as building acoustics) involves the scientific understanding of how to achieve good sound within a building. It typically involves the study of speech intelligibility, speech privacy, music quality, and vibration reduction in the built environment. Commonly studied environments are hospitals, classrooms, dwellings, performance venues, recording and broadcasting studios. Focus considerations include room acoustics, airborne and impact transmission in building structures, airborne and structure-borne noise control, noise control of building systems and electroacoustic systems.

Bioacoustics
Bioacoustics is the scientific study of the hearing and calls of animal calls, as well as how animals are affected by the acoustic and sounds of their habitat.

Electroacoustics
This subdiscipline is concerned with the recording, manipulation and reproduction of audio using electronics. This might include products such as mobile phones, large scale public address systems or virtual reality systems in research laboratories.

Environmental noise and soundscapes
Environmental acoustics is concerned with noise and vibration caused by railways, road traffic, aircraft, industrial equipment and recreational activities. The main aim of these studies is to reduce levels of environmental noise and vibration. Research work now also has a focus on the positive use of sound in urban environments: soundscapes and tranquility.

Musical acoustics
Musical acoustics is the study of the physics of acoustic instruments; the audio signal processing used in electronic music; the computer analysis of music and composition, and the perception and cognitive neuroscience of music.

Noise
The goal this acoustics sub-discipline is to reduce the impact of unwanted sound. Scope of noise studies includes the generation, propagation, and impact on structures, objects, and people. Noise research investigates the impact of noise on humans and animals to include work in definitions, abatement, transportation noise, hearing protection, Jet and rocket noise, building system noise and vibration, atmospheric sound propagation, soundscapes, and low-frequency sound.
 * Innovative model development
 * Measurement techniques
 * Mitigation strategies
 * Input to the establishment of standards and regulations

Psychoacoustics
Many studies have been conducted to identify the relationship between acoustics and cognition, or more commonly known as psychoacoustics, in which what one hears is a combination of perception and biological aspects. The information intercepted by the passage of sound waves through the ear is understood and interpreted through the brain, emphasizing the connection between the mind and acoustics. Psychological changes have been seen as brain waves slow down or speed up as a result of varying auditory stimulus which can in turn affect the way one thinks, feels, or even behaves. This correlation can be viewed in normal, everyday situations in which listening to an upbeat or uptempo song can cause one's foot to start tapping or a slower song can leave one feeling calm and serene. In a deeper biological look at the phenomenon of psychoacoustics, it was discovered that the central nervous system is activated by basic acoustical characteristics of music. By observing how the central nervous system, which includes the brain and spine, is influenced by acoustics, the pathway in which acoustic affects the mind, and essentially the body, is evident.

Speech
Acousticians study the production, processing and perception of speech. Speech recognition and Speech synthesis are two important areas of speech processing using computers. The subject also overlaps with the disciplines of physics, physiology, psychology, and linguistics.

Structural Vibration and Dynamics
Structural acoustics is the study of motions and interactions of mechanical systems with their environments and the methods of their measurement, analysis, and control. There are several sub-disciplines found within this regime:
 * Modal Analysis
 * Material characterization
 * Structural health monitoring
 * Acoustic Metamaterials
 * Friction Acoustics

Applications might include: ground vibrations from railways; vibration isolation to reduce vibration in operating theatres; studying how vibration can damage health (vibration white finger); vibration control to protect a building from earthquakes, or measuring how structure-borne sound moves through buildings.

Ultrasonics

Ultrasonics deals with sounds at frequencies too high to be heard by humans. Specialisms include medical ultrasonics (including medical ultrasonography), sonochemistry, ultrasonic testing, material characterisation and underwater acoustics (sonar).

Underwater acoustics
Underwater acoustics is the scientific study of natural and man-made sounds underwater. Applications include sonar to locate submarines, underwater communication by whales, climate change monitoring by measuring sea temperatures acoustically, sonic weapons, and marine bioacoustics.

Acoustic Conferences

 * InterNoise
 * NoiseCon
 * Forum Acousticum
 * SAE Noise and Vibration Conference and Exhibition

Professional societies

 * The Acoustical Society of America (ASA)
 * Australian Acoustical Society (AAS)
 * The European Acoustics Association (EAA)
 * Institute of Electrical and Electronics Engineers (IEEE)
 * Institute of Acoustics (IoA UK)
 * The Audio Engineering Society (AES)
 * American Society of Mechanical Engineers, Noise Control and Acoustics Division (ASME-NCAD)
 * International Commission for Acoustics (ICA)
 * American Institute of Aeronautics and Astronautics, Aeroacoustics (AIAA)
 * International Computer Music Association (ICMA)

Academic journals

 * Acoustics | An Open Access Journal from MDPI
 * Acoustics Today
 * Acta Acustica united with Acustica
 * Advances in Acoustics and Vibration
 * Applied Acoustics
 * Building Acoustics
 * IEEE Transacions on Ultrasonics, Ferroelectrics, and Frequency Control
 * Journal of the Acoustical Society of America (JASA)
 * Journal of the Acoustical Society of America, Express Letters (JASA-EL)
 * Journal of the Audio Engineering Society
 * Journal of Sound and Vibration (JSV)
 * Journal of Vibration and Acoustics American Society of Mechanical Engineers
 * MDPI Acoustics
 * Noise Control Engineering Journal
 * SAE International Journal of Vehicle Dynamics, Stability and NVH
 * Ultrasonics (journal)
 * Ultrasonics Sonochemistry
 * Wave Motion

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Atomic physics

Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned with the way in which electrons are arranged around the nucleus and the processes by which these arrangements change. This comprises ions, neutral atoms and, unless otherwise stated, it can be assumed that the term atom includes ions.

The term atomic physics can be associated with nuclear power and nuclear weapons, due to the synonymous use of atomic and nuclear in standard English. Physicists distinguish between atomic physics—which deals with the atom as a system consisting of a nucleus and electrons—and nuclear physics, which studies nuclear reactions and special properties of atomic nuclei.

As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of atomic, molecular, and optical physics. Physics research groups are usually so classified.

Isolated atoms
Atomic physics primarily considers atoms in isolation. Atomic models will consist of a single nucleus that may be surrounded by one or more bound electrons. It is not concerned with the formation of molecules (although much of the physics is identical), nor does it examine atoms in a solid state as condensed matter. It is concerned with processes such as ionization and excitation by photons or collisions with atomic particles.

While modelling atoms in isolation may not seem realistic, if one considers atoms in a gas or plasma then the time-scales for atom-atom interactions are huge in comparison to the atomic processes that are generally considered. This means that the individual atoms can be treated as if each were in isolation, as the vast majority of the time they are. By this consideration, atomic physics provides the underlying theory in plasma physics and atmospheric physics, even though both deal with very large numbers of atoms.

Electronic configuration
Electrons form notional shells around the nucleus. These are normally in a ground state but can be excited by the absorption of energy from light (photons), magnetic fields, or interaction with a colliding particle (typically ions or other electrons).

Electrons that populate a shell are said to be in a bound state. The energy necessary to remove an electron from its shell (taking it to infinity) is called the binding energy. Any quantity of energy absorbed by the electron in excess of this amount is converted to kinetic energy according to the conservation of energy. The atom is said to have undergone the process of ionization.

If the electron absorbs a quantity of energy less than the binding energy, it will be transferred to an excited state. After a certain time, the electron in an excited state will "jump" (undergo a transition) to a lower state. In a neutral atom, the system will emit a photon of the difference in energy, since energy is conserved.

If an inner electron has absorbed more than the binding energy (so that the atom ionizes), then a more outer electron may undergo a transition to fill the inner orbital. In this case, a visible photon or a characteristic X-ray is emitted, or a phenomenon known as the Auger effect may take place, where the released energy is transferred to another bound electron, causing it to go into the continuum. The Auger effect allows one to multiply ionize an atom with a single photon.

There are rather strict selection rules as to the electronic configurations that can be reached by excitation by light — however, there are no such rules for excitation by collision processes.

History and developments
One of the earliest steps towards atomic physics was the recognition that matter was composed of atoms. It forms a part of the texts written in 6th century BC to 2nd century BC, such as those of Democritus or Vaiśeṣika Sūtra written by Kaṇāda. This theory was later developed in the modern sense of the basic unit of a chemical element by the British chemist and physicist John Dalton in the 18th century. At this stage, it wasn't clear what atoms were, although they could be described and classified by their properties (in bulk). The invention of the periodic system of elements by Dmitri Mendeleev was another great step forward.

The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics. In seeking to explain atomic spectra, an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this yield a better overall description, i.e. the atomic orbital model, but it also provided a new theoretical basis for chemistry (quantum chemistry) and spectroscopy.

Since the Second World War, both theoretical and experimental fields have advanced at a rapid pace. This can be attributed to progress in computing technology, which has allowed larger and more sophisticated models of atomic structure and associated collision processes. Similar technological advances in accelerators, detectors, magnetic field generation and lasers have greatly assisted experimental work.

Significant atomic physicists
• ; Pre quantum mechanics

• John Dalton

• Joseph von Fraunhofer

• Johannes Rydberg

• J. J. Thomson

• Ernest Rutherford

• Democritus

• Vaiśeṣika Sūtra

• ; Post quantum mechanics

• Alexander Dalgarno

• David Bates

• Niels Bohr

• Max Born

• Clinton Joseph Davisson

• Paul A. M. Dirac

• Enrico Fermi

• Charlotte Froese Fischer

• Vladimir Fock

• Douglas Hartree

• Ernest M. Henley

• Ratko Janev

• Daniel Kleppner

• Harrie S. Massey

• Nevill Mott

• I. I. Rabi

• Norman Ramsey

• Mike Seaton

• John C. Slater

• George Paget Thomson

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Atomic physics


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American Sign Language

American Sign Language (ASL) is a natural language that serves as the predominant sign language of deaf communities in the United States and most of Anglophone Canada. ASL is a complete and organized visual language that is expressed by employing both manual and nonmanual features. Besides North America, dialects of ASL and ASL-based creoles are used in many countries around the world, including much of West Africa and parts of Southeast Asia. ASL is also widely learned as a second language, serving as a lingua franca. ASL is most closely related to French Sign Language (LSF). It has been proposed that ASL is a creole language of LSF, although ASL shows features atypical of creole languages, such as agglutinative morphology.

ASL originated in the early 19th century in the American School for the Deaf (ASD) in Hartford, Connecticut, from a situation of language contact. Since then, ASL use has been propagated widely by schools for the deaf and Deaf community organizations. Despite its wide use, no accurate count of ASL users has been taken. Reliable estimates for American ASL users range from 250,000 to 500,000 persons, including a number of children of deaf adults and other hearing individuals.

ASL signs have a number of phonemic components, such as movement of the face, the torso, and the hands. ASL is not a form of pantomime although iconicity plays a larger role in ASL than in spoken languages. English loan words are often borrowed through fingerspelling, although ASL grammar is unrelated to that of English. ASL has verbal agreement and aspectual marking and has a productive system of forming agglutinative classifiers. Many linguists believe ASL to be a subject–verb–object language. However, there are several alternative proposals to account for ASL word order.

Classification

ASL emerged as a language in the American School for the Deaf (ASD), founded by Thomas Gallaudet in 1817, which brought together Old French Sign Language, various village sign languages, and home sign systems. ASL was created in that situation by language contact. ASL was influenced by its forerunners but distinct from all of them.

The influence of French Sign Language (LSF) on ASL is readily apparent; for example, it has been found that about 58% of signs in modern ASL are cognate to Old French Sign Language signs. However, that is far less than the standard 80% measure used to determine whether related languages are actually dialects. That suggests that nascent ASL was highly affected by the other signing systems brought by the ASD students although the school's original director, Laurent Clerc, taught in LSF. In fact, Clerc reported that he often learned the students' signs rather than conveying LSF: "I see, however, and I say it with regret, that any efforts that we have made or may still be making, to do better than, we have inadvertently fallen somewhat back of Abbé de l'Épée. Some of us have learned and still learn signs from uneducated pupils, instead of learning them from well instructed and experienced teachers."

It has been proposed that ASL is a creole in which LSF is the superstrate language and the native village sign languages are substrate languages. However, more recent research has shown that modern ASL does not share many of the structural features that characterize creole languages. ASL may have begun as a creole and then undergone structural change over time, but it is also possible that it was never a creole-type language. There are modality-specific reasons that sign languages tend towards agglutination, such as the ability to simultaneously convey information via the face, head, torso, and other body parts. That might override creole characteristics such as the tendency towards isolating morphology. Additionally, Clerc and Thomas Hopkins Gallaudet may have used an artificially constructed form of manually coded language in instruction rather than true LSF.

Although the United States, the United Kingdom, and Australia share English as a common oral and written language, ASL is not mutually intelligible with either British Sign Language (BSL) or Auslan. All three languages show degrees of borrowing from English, but that alone is not sufficient for cross-language comprehension. It has been found that a relatively high percentage (37–44%) of ASL signs have similar translations in Auslan, which for oral languages would suggest that they belong to the same language family. However, that does not seem justified historically for ASL and Auslan, and it is likely that the resemblance is caused by the higher degree of iconicity in sign languages in general as well as contact with English.

American Sign Language is growing in popularity in many states. Many high school and university students desire to take it as a foreign language, but until recently, it was usually not considered a creditable foreign language elective. ASL users, however, have a very distinct culture, and they interact very differently when they talk. Their facial expressions and hand movements reflect what they are communicating. They also have their own sentence structure, which sets the language apart.

American Sign Language is now being accepted by many colleges as a language eligible for foreign language course credit; many states are making it mandatory to accept it as such. In some states however, this is only true with regard to high school coursework.

History
Prior to the birth of ASL, sign language had been used by various communities in the United States. In the United States, as elsewhere in the world, hearing families with deaf children have historically employed ad hoc home sign, which often reaches much higher levels of sophistication than gestures used by hearing people in spoken conversation. As early as 1541 at first contact by Francisco Vásquez de Coronado, there were reports that the Indigenous peoples of the Great Plains widely spoke a sign language to communicate across vast national and linguistic lines.

In the 19th century, a "triangle" of village sign languages developed in New England: one in Martha's Vineyard, Massachusetts; one in Henniker, New Hampshire, and one in Sandy River Valley, Maine. Martha's Vineyard Sign Language (MVSL), which was particularly important for the history of ASL, was used mainly in Chilmark, Massachusetts. Due to intermarriage in the original community of English settlers of the 1690s, and the recessive nature of genetic deafness, Chilmark had a high 4% rate of genetic deafness. MVSL was used even by hearing residents whenever a deaf person was present, and also in some situations where spoken language would be ineffective or inappropriate, such as during church sermons or between boats at sea.

ASL is thought to have originated in the American School for the Deaf (ASD), founded in Hartford, Connecticut, in 1817. Originally known as The American Asylum, At Hartford, For The Education And Instruction Of The Deaf And Dumb, the school was founded by the Yale graduate and divinity student Thomas Hopkins Gallaudet. Gallaudet, inspired by his success in demonstrating the learning abilities of a young deaf girl Alice Cogswell, traveled to Europe in order to learn deaf pedagogy from European institutions. Ultimately, Gallaudet chose to adopt the methods of the French Institut National de Jeunes Sourds de Paris, and convinced Laurent Clerc, an assistant to the school's founder Charles-Michel de l'Épée, to accompany him back to the United States. Upon his return, Gallaudet founded the ASD on April 15, 1817.

The largest group of students during the first seven decades of the school were from Martha's Vineyard, and they brought MVSL with them. There were also 44 students from around Henniker, New Hampshire, and 27 from the Sandy River valley in Maine, each of which had their own village sign language. Other students brought knowledge of their own home signs. Laurent Clerc, the first teacher at ASD, taught using French Sign Language (LSF), which itself had developed in the Parisian school for the deaf established in 1755. From that situation of language contact, a new language emerged, now known as ASL.

More schools for the deaf were founded after ASD, and knowledge of ASL spread to those schools. In addition, the rise of Deaf community organizations bolstered the continued use of ASL. Societies such as the National Association of the Deaf and the National Fraternal Society of the Deaf held national conventions that attracted signers from across the country. All of that contributed to ASL's wide use over a large geographical area, atypical of a sign language.

While oralism, an approach to educating deaf students focusing on oral language, had previously been used in American schools, the Milan Congress made it dominant and effectively banned the use of sign languages at schools in the United States and Europe. However, the efforts of Deaf advocates and educators, more lenient enforcement of the Congress's mandate, and the use of ASL in religious education and proselytism ensured greater use and documentation compared to European sign languages, albeit more influenced by fingerspelled loanwords and borrowed idioms from English as students were societally pressured to achieve fluency in spoken language. Nevertheless, oralism remained the predominant method of deaf education up to the 1950s. Linguists did not consider sign language to be true "language" but as something inferior. Recognition of the legitimacy of ASL was achieved by William Stokoe, a linguist who arrived at Gallaudet University in 1955 when that was still the dominant assumption. Aided by the Civil Rights Movement of the 1960s, Stokoe argued for manualism, the use of sign language in deaf education. Stokoe noted that sign language shares the important features that oral languages have as a means of communication, and even devised a transcription system for ASL. In doing so, Stokoe revolutionized both deaf education and linguistics. In the 1960s, ASL was sometimes referred to as "Ameslan", but that term is now considered obsolete.

Population
Counting the number of ASL signers is difficult because ASL users have never been counted by the American census. The ultimate source for current estimates of the number of ASL users in the United States is a report for the National Census of the Deaf Population (NCDP) by Schein and Delk (1974). Based on a 1972 survey of the NCDP, Schein and Delk provided estimates consistent with a signing population between 250,000 and 500,000. The survey did not distinguish between ASL and other forms of signing; in fact, the name "ASL" was not yet in widespread use.

Incorrect figures are sometimes cited for the population of ASL users in the United States based on misunderstandings of known statistics. Demographics of the deaf population have been confused with those of ASL use since adults who become deaf late in life rarely use ASL in the home. That accounts for currently-cited estimations that are greater than 500,000; such mistaken estimations can reach as high as 15,000,000. A 100,000-person lower bound has been cited for ASL users; the source of that figure is unclear, but it may be an estimate of prelingual deafness, which is correlated with but not equivalent to signing.

ASL is sometimes incorrectly cited as the third- or fourth-most-spoken language in the United States. Those figures misquote Schein and Delk (1974), who actually concluded that ASL speakers constituted the third-largest population "requiring an interpreter in court". Although that would make ASL the third-most used language among monolinguals other than English, it does not imply that it is the fourth-most-spoken language in the United States since speakers of other languages may also speak English.

Geographic distribution
ASL is used throughout Anglo-America. That contrasts with Europe, where a variety of sign languages are used within the same continent. The unique situation of ASL seems to have been caused by the proliferation of ASL through schools influenced by the American School for the Deaf, wherein ASL originated, and the rise of community organizations for the Deaf.

Throughout West Africa, ASL-based sign languages are signed by educated Deaf adults. Such languages, imported by boarding schools, are often considered by associations to be the official sign languages of their countries and are named accordingly, such as Nigerian Sign Language, Ghanaian Sign Language. Such signing systems are found in Benin, Burkina Faso, Ivory Coast, Ghana, Liberia, Mauritania, Mali, Nigeria, and Togo. Due to lack of data, it is still an open question how similar those sign languages are to the variety of ASL used in America.

In addition to the aforementioned West African countries, ASL is reported to be used as a first language in Barbados, Bolivia, Cambodia (alongside Cambodian Sign Language), the Central African Republic, Chad, China (Hong Kong), the Democratic Republic of the Congo, Gabon, Jamaica, Kenya, Madagascar, the Philippines, Singapore, and Zimbabwe. ASL is also used as a lingua franca throughout the deaf world, widely learned as a second language.

Sign production
Sign production can often vary according to location. Signers from the South tend to sign with more flow and ease. Native signers from New York have been reported as signing comparatively quicker and sharper. Sign production of native Californian signers has also been reported as being fast. Research on that phenomenon often concludes that the fast-paced production for signers from the coasts could be due to the fast-paced nature of living in large metropolitan areas. That conclusion also supports how the ease with which Southerners sign could be caused by the easygoing environment of the South in comparison to that of the coasts.

Sign production can also vary depending on age and native language. For example, sign production of letters may vary in older signers. Slight differences in finger spelling production can be a signal of age. Additionally, signers who learned American Sign Language as a second language vary in production. For Deaf signers who learned a different sign language before learning American Sign Language, qualities of their native language may show in their ASL production. Some examples of that varied production include fingerspelling towards the body, instead of away from it, and signing certain movement from bottom to top, instead of top to bottom. Hearing people who learn American Sign Language also have noticeable differences in signing production. The most notable production difference of hearing people learning American Sign Language is their rhythm and arm posture.

Sign variants
Most popularly, there are variants of the signs for English words such as "birthday", "pizza", "Halloween", "early", and "soon", just a sample of the most commonly recognized signs with variants based on regional change. The sign for "school" is commonly varied between black and white signers; the variants used by black signers are sometimes called Black American Sign Language. Social variation is also found between citation forms and forms used by Deaf gay men for words such as "pain" and "protest".

History and implications
The prevalence of residential Deaf schools can account for much of the regional variance of signs and sign productions across the United States. Deaf schools often serve students of the state in which the school resides. That limited access to signers from other regions, combined with the residential quality of Deaf Schools promoted specific use of certain sign variants. Native signers did not have much access to signers from other regions during the beginning years of their education. It is hypothesized that because of that seclusion, certain variants of a sign prevailed over others due to the choice of variant used by the student of the school/signers in the community.

However, American Sign Language does not appear to be vastly varied in comparison to other signed languages. That is because when Deaf education was beginning in the United States, many educators flocked to the American School for the Deaf in Hartford, Connecticut, whose central location for the first generation of educators in Deaf education to learn American Sign Language allows ASL to be more standardized than its variant.

Varieties
Varieties of ASL are found throughout the world. There is little difficulty in comprehension among the varieties of the United States and Canada.

"Just as there are accents in speech, there are regional accents in sign. People from the South sign slower than people in the North—even people from northern and southern Indiana have different styles."

Mutual intelligibility among those ASL varieties is high, and the variation is primarily lexical. For example, there are three different words for English about in Canadian ASL; the standard way, and two regional variations (Atlantic and Ontario). Variation may also be phonological, meaning that the same sign may be signed in a different way depending on the region. For example, an extremely common type of variation is between the handshapes /1/, /L/, and /5/ in signs with one handshape.

There is also a distinct variety of ASL used by the Black Deaf community. Black ASL evolved as a result of racially segregated schools in some states, which included the residential schools for the deaf. Black ASL differs from standard ASL in vocabulary, phonology, and some grammatical structure. While African American English (AAE) is generally viewed as more innovating than standard English, Black ASL is more conservative than standard ASL, preserving older forms of many signs. Black sign language speakers use more two-handed signs than in mainstream ASL, are less likely to show assimilatory lowering of signs produced on the forehead (e.g. KNOW) and use a wider signing space. Modern Black ASL borrows a number of idioms from AAE; for instance, the AAE idiom "I feel you" is calqued into Black ASL.

ASL is used internationally as a lingua franca, and a number of closely related sign languages derived from ASL are used in many different countries. Even so, there have been varying degrees of divergence from standard ASL in those imported ASL varieties. Bolivian Sign Language is reported to be a dialect of ASL, no more divergent than other acknowledged dialects. On the other hand, it is also known that some imported ASL varieties have diverged to the extent of being separate languages. For example, Malaysian Sign Language, which has ASL origins, is no longer mutually comprehensible with ASL and must be considered its own language. For some imported ASL varieties, such as those used in West Africa, it is still an open question how similar they are to American ASL.

When communicating with hearing English speakers, ASL-speakers often use what is commonly called Pidgin Signed English (PSE) or 'contact signing', a blend of English structure with ASL vocabulary. Various types of PSE exist, ranging from highly English-influenced PSE (practically relexified English) to PSE which is quite close to ASL lexically and grammatically, but may alter some subtle features of ASL grammar. Fingerspelling may be used more often in PSE than it is normally used in ASL. There have been some constructed sign languages, known as Manually Coded English (MCE), which match English grammar exactly and simply replace spoken words with signs; those systems are not considered to be varieties of ASL.

Tactile ASL (TASL) is a variety of ASL used throughout the United States by and with the deaf-blind. It is particularly common among those with Usher's syndrome. It results in deafness from birth followed by loss of vision later in life; consequently, those with Usher's syndrome often grow up in the Deaf community using ASL, and later transition to TASL. TASL differs from ASL in that signs are produced by touching the palms, and there are some grammatical differences from standard ASL in order to compensate for the lack of nonmanual signing.

ASL changes over time and from generation to generation. The sign for telephone has changed as the shape of phones and the manner of holding them have changed. The development of telephones with screens has also changed ASL, encouraging the use of signs that can be seen on small screens.

Stigma
In 2013, the White House published a response to a petition that gained over 37,000 signatures to officially recognize American Sign Language as a community language and a language of instruction in schools. The response is titled "there shouldn't be any stigma about American Sign Language" and addressed that ASL is a vital language for the Deaf and hard of hearing. Stigmas associated with sign languages and the use of sign for educating children often lead to the absence of sign during periods in children's lives when they can access languages most effectively. Scholars such as Beth S. Benedict advocate not only for bilingualism (using ASL and English training) but also for early childhood intervention for children who are deaf. York University psychologist Ellen Bialystok has also campaigned for bilingualism, arguing that those who are bilingual acquire cognitive skills that may help to prevent dementia later in life.

Most children born to deaf parents are hearing. Known as CODAs ("Children Of Deaf Adults"), they are often more culturally Deaf than deaf children, most of whom are born to hearing parents. Unlike many deaf children, CODAs acquire ASL as well as Deaf cultural values and behaviors from birth. Such bilingual hearing children may be mistakenly labeled as being "slow learners" or as having "language difficulties" because of preferential attitudes towards spoken language.

Writing systems
Although there is no well-established writing system for ASL, written sign language dates back almost two centuries. The first systematic writing system for a sign language seems to be that of Roch-Ambroise Auguste Bébian, developed in 1825. However, written sign language remained marginal among the public. In the 1960s, linguist William Stokoe created Stokoe notation specifically for ASL. It is alphabetic, with a letter or diacritic for every phonemic (distinctive) hand shape, orientation, motion, and position, though it lacks any representation of facial expression, and is better suited for individual words than for extended passages of text. Stokoe used that system for his 1965 A Dictionary of American Sign Language on Linguistic Principles.

SignWriting, proposed in 1974 by Valerie Sutton, is the first writing system to gain use among the public and the first writing system for sign languages to be included in the Unicode Standard. SignWriting consists of more than 5000 distinct iconic graphs/glyphs. Currently, it is in use in many schools for the Deaf, particularly in Brazil, and has been used in International Sign forums with speakers and researchers in more than 40 countries, including Brazil, Ethiopia, France, Germany, Italy, Portugal, Saudi Arabia, Slovenia, Tunisia, and the United States. Sutton SignWriting has both a printed and an electronically produced form so that persons can use the system anywhere that oral languages are written (personal letters, newspapers, and media, academic research). The systematic examination of the International Sign Writing Alphabet (ISWA) as an equivalent usage structure to the International Phonetic Alphabet for spoken languages has been proposed. According to some researchers, SignWriting is not a phonemic orthography and does not have a one-to-one map from phonological forms to written forms. That assertion has been disputed, and the process for each country to look at the ISWA and create a phonemic/morphemic assignment of features of each sign language was proposed by researchers Msc. Roberto Cesar Reis da Costa and Madson Barreto in a thesis forum on June 23, 2014. The SignWriting community has an open project on Wikimedia Labs to support the various Wikimedia projects on Wikimedia Incubator and elsewhere involving SignWriting. The ASL Wikipedia request was marked as eligible in 2008 and the test ASL Wikipedia has 50 articles written in ASL using SignWriting.

The most widely used transcription system among academics is HamNoSys, developed at the University of Hamburg. Based on Stokoe Notation, HamNoSys was expanded to about 200 graphs in order to allow transcription of any sign language. Phonological features are usually indicated with single symbols, though the group of features that make up a handshape is indicated collectively with a symbol.

Several additional candidates for written ASL have appeared over the years, including SignFont, ASL-phabet, and Si5s.

For English-speaking audiences, ASL is often glossed using English words. Such glosses are typically all-capitalized and are arranged in ASL order. For example, the ASL sentence DOG NOW CHASE>IX=3 CAT, meaning "the dog is chasing the cat", uses NOW to mark ASL progressive aspect and shows ASL verbal inflection for the third person (>IX=3). However, glossing is not used to write the language for speakers of ASL.

Phonology
Each sign in ASL is composed of a number of distinctive components, generally referred to as parameters. A sign may use one hand or both. All signs can be described using the five parameters involved in signed languages, which are handshape, movement, palm orientation, location and nonmanual markers. Just as phonemes of sound distinguish meaning in spoken languages, those parameters are the phonemes that distinguish meaning in signed languages like ASL. Changing any one of them may change the meaning of a sign, as illustrated by the ASL signs THINK and DISAPPOINTED:

There are also meaningful nonmanual signals in ASL, which may include movement of the eyebrows, the cheeks, the nose, the head, the torso, and the eyes.

William Stokoe proposed that such components are analogous to the phonemes of spoken languages. There has also been a proposal that they are analogous to classes like place and manner of articulation. As in spoken languages, those phonological units can be split into distinctive features. For instance, the handshapes /2/ and /3/ are distinguished by the presence or absence of the feature [± closed thumb], as illustrated to the right. ASL has processes of allophony and phonotactic restrictions. There is ongoing research into whether ASL has an analog of syllables in spoken language.

Morphology
ASL has a rich system of verbal inflection, which involves both grammatical aspect: how the action of verbs flows in time—and agreement marking. Aspect can be marked by changing the manner of movement of the verb; for example, continuous aspect is marked by incorporating rhythmic, circular movement, while punctual aspect is achieved by modifying the sign so that it has a stationary hand position. Verbs may agree with both the subject and the object, and are marked for number and reciprocity. Reciprocity is indicated by using two one-handed signs; for example, the sign SHOOT, made with an L-shaped handshape with inward movement of the thumb, inflects to SHOOT[reciprocal], articulated by having two L-shaped hands "shooting" at each other.

ASL has a productive system of classifiers, which are used to classify objects and their movement in space. For example, a rabbit running downhill would use a classifier consisting of a bent V classifier handshape with a downhill-directed path; if the rabbit is hopping, the path is executed with a bouncy manner. In general, classifiers are composed of a "classifier handshape" bound to a "movement root". The classifier handshape represents the object as a whole, incorporating such attributes as surface, depth, and shape, and is usually very iconic. The movement root consists of a path, a direction and a manner.

In linguistics, there are two primary ways of changing the form of a word: derivation and inflection. Derivation involves creating new words by adding something to an existing word, while inflection involves changing the form of a word to convey grammatical information without altering its fundamental meaning or category.

For example, adding the suffix "-ship" to the noun "friend" creates the new word "friendship", which has a different meaning than the original word. Inflection, on the other hand, involves modifying a word's form to indicate grammatical features such as tense, number, gender, person, case, and degree of comparison.

In American Sign Language (ASL), inflection is conveyed through facial expressions, body movements, and other non-manual markers. For instance, to indicate past tense in ASL, one might sign the present tense of a verb (such as "walk"), and then add a facial expression and head tilt to signify that the action occurred in the past (i.e., "walked").

While inflection does not change the basic meaning or category of a word, it does provide additional information that helps us better understand how the word is being used in a sentence. This is similar to how subtitles in a movie provide additional information without altering the content of the film itself.

According to the book Linguistics of American Sign Language, ASL signs have two main components: hold segments and movement segments. Hold segments consist of hand-shape, location, orientation, and non-manual features, while movement segments possess similar features.

Morphology is the study of how languages form words by using smaller units to construct larger units. The smallest meaningful unit in a language is known as a "morpheme", with some morphemes able to stand alone as independent units (free morphemes), while others must occur with other morphemes (bound morphemes).

For example, the plural "-s" and third person "-s" in English are bound morphemes. In ASL, the 3 handshape in signs like THREE-WEEKS and THREE-MONTHS are also bound morphemes.

Affixes, which are morphemes added to words to create new words or modify their meanings, are part of the derivational process. For example, in English, prefixes like "re-" and suffixes like "-able" are affixes. In ASL, affixation can be used to modify the sign for CHAIR to indicate different types of chairs. The inflectional process, on the other hand, adds grammatical information to existing units.

By studying morphemes and how they can be combined or modified, linguists gain insight into the underlying structure of language and the creative ways in which it can be used to express meaning. Understanding morphology is essential to understanding how languages are built and how new signs or words can be formed.

Furthermore, understanding morphology has practical applications in language learning and teaching. For example, teaching students the basic morphological structures of a language can help them to better understand the language's grammar and syntax, and can also aid in their acquisition of new vocabulary.

In summary, morphology is an essential component of language and provides valuable insights into the structure and function of languages. By understanding the morphological processes involved in language formation, we can gain a deeper understanding of how languages work and how they can be effectively taught and learned.

Fingerspelling
American Sign Language possesses a set of 26 signs known as the American manual alphabet, which can be used to spell out words from the English language. It is rather a representation of the English alphabet, and not a unique alphabet of ASL, although commonly labeled as the "ASL alphabet". It is borrowed from French Sign Language (LSF), as much of ASL is derived from LSF. Such signs make use of the 19 handshapes of ASL. For example, the signs for 'p' and 'k' use the same handshape but different orientations. A common misconception is that ASL consists only of fingerspelling; although such a method (Rochester Method) has been used, it is not ASL.

Fingerspelling is a form of borrowing, a linguistic process wherein words from one language are incorporated into another. In ASL, fingerspelling is used for proper nouns and for technical terms with no native ASL equivalent. There are also some other loan words which are fingerspelled, either very short English words or abbreviations of longer English words, e.g. O-N from English 'on', and A-P-T from English 'apartment'. Fingerspelling may also be used to emphasize a word that would normally be signed otherwise.

Syntax
ASL is a subject–verb–object (SVO) language, but various phenomena affect that basic word order. Basic SVO sentences are signed without any pauses:

FATHER LOVE CHILD

"The father loves the child."

However, other word orders may also occur since ASL allows the topic of a sentence to be moved to sentence-initial position, a phenomenon known as topicalization. In object–subject–verb (OSV) sentences, the object is topicalized, marked by a forward head-tilt and a pause:

CHILDtopic, FATHER LOVE

"The father loves the child."

Besides, word orders can be obtained through the phenomenon of subject copy in which the subject is repeated at the end of the sentence, accompanied by head nodding for clarification or emphasis:

FATHER LOVE CHILD FATHERcopy

"The father loves the child."

ASL also allows null subject sentences whose subject is implied, rather than stated explicitly. Subjects can be copied even in a null subject sentence, and the subject is then omitted from its original position, yielding a verb–object–subject (VOS) construction:

LOVE CHILD FATHERcopy

"The father loves the child."

Topicalization, accompanied with a null subject and a subject copy, can produce yet another word order, object–verb–subject (OVS).

CHILDtopic, LOVE FATHERcopy

"The father loves the child."

Those properties of ASL allow it a variety of word orders, leading many to question which is the true, underlying, "basic" order. There are several other proposals that attempt to account for the flexibility of word order in ASL. One proposal is that languages like ASL are best described with a topic–comment structure whose words are ordered by their importance in the sentence, rather than by their syntactic properties. Another hypothesis is that ASL exhibits free word order, in which syntax is not encoded in word order but can be encoded by other means such as head nods, eyebrow movement, and body position.

Iconicity
Common misconceptions are that signs are iconically self-explanatory, that they are a transparent imitation of what they mean, or even that they are pantomime. In fact, many signs bear no resemblance to their referent because they were originally arbitrary symbols, or their iconicity has been obscured over time. Even so, in ASL iconicity plays a significant role; a high percentage of signs resemble their referents in some way. That may be because the medium of sign, three-dimensional space, naturally allows more iconicity than oral language.

In the era of the influential linguist Ferdinand de Saussure, it was assumed that the mapping between form and meaning in language must be completely arbitrary. Although onomatopoeia is a clear exception, since words like "choo-choo" bear clear resemblance to the sounds that they mimic, the Saussurean approach was to treat them as marginal exceptions. ASL, with its significant inventory of iconic signs, directly challenges that theory.

Research on acquisition of pronouns in ASL has shown that children do not always take advantage of the iconic properties of signs when they interpret their meaning. It has been found that when children acquire the pronoun "you", the iconicity of the point (at the child) is often confused, being treated more like a name. That is a similar finding to research in oral languages on pronoun acquisition. It has also been found that iconicity of signs does not affect immediate memory and recall; less iconic signs are remembered just as well as highly-iconic signs.

title: American Sign Language


text:
Applet

In computing, an applet is any small application that performs one specific task that runs within the scope of a dedicated widget engine or a larger program, often as a plug-in. The term is frequently used to refer to a Java applet, a program written in the Java programming language that is designed to be placed on a web page. Applets are typical examples of transient and auxiliary applications that do not monopolize the user's attention. Applets are not full-featured application programs, and are intended to be easily accessible.

History
The word applet was first used in 1990 in PC Magazine. However, the concept of an applet, or more broadly a small interpreted program downloaded and executed by the user, dates at least to RFC 5 (1969) by Jeff Rulifson, which described the Decode-Encode Language, which was designed to allow remote use of the oN-Line System over ARPANET, by downloading small programs to enhance the interaction. This has been specifically credited as a forerunner of Java's downloadable programs in RFC 2555.

Applet as an extension of other software
In some cases, an applet does not run independently. These applets must run either in a container provided by a host program, through a plugin, or a variety of other applications including mobile devices that support the applet programming model.

Web-based applets
Applets were used to provide interactive features to web applications that historically could not be provided by HTML alone. They could capture mouse input and also had controls like buttons or check boxes. In response to the user action, an applet could change the provided graphic content. This made applets well suited for demonstration, visualization, and teaching. There were online applet collections for studying various subjects, from physics to heart physiology. Applets were also used to create online game collections that allowed players to compete against live opponents in real-time.

An applet could also be a text area only, providing, for instance, a cross-platform command-line interface to some remote system. If needed, an applet could leave the dedicated area and run as a separate window. However, applets had very little control over web page content outside the applet dedicated area, so they were less useful for improving the site appearance in general (while applets like news tickers or WYSIWYG editors are also known). Applets could also play media in formats that are not natively supported by the browser.

HTML pages could embed parameters that were passed to the applet. Hence, the same applet could appear differently depending on the parameters that were passed.

Examples of Web-based applets include:

 * QuickTime movies
 * Flash movies
 * Windows Media Player applets, used to display embedded video files in Internet Explorer (and other browsers that supported the plugin)
 * 3D modeling display applets, used to rotate and zoom a model
 * Browser games that were applet-based, though some developed into fully functional applications that required installation.

Applet Vs. Subroutine
A larger application distinguishes its applets through several features:

 * Applets execute only on the "client" platform environment of a system, as contrasted from "Servlet". As such, an applet provides functionality or performance beyond the default capabilities of its container (the browser).
 * The container restricts applets' capabilities.
 * Applets are written in a language different from the scripting or HTML language that invokes it. The applet is written in a compiled language, whereas the scripting language of the container is an interpreted language, hence the greater performance or functionality of the applet. Unlike a subroutine, a complete web component can be implemented as an applet.

Java applets
A Java applet is a Java program that is launched from HTML and run in a web browser. It takes code from server and run in a web browser. It can provide web applications with interactive features that cannot be provided by HTML. Since Java's bytecode is platform-independent, Java applets can be executed by browsers running under many platforms, including Windows, Unix, macOS, and Linux. When a Java technology-enabled web browser processes a page that contains an applet, the applet's code is transferred to the client's system and executed by the browser's Java virtual machine. An HTML page references an applet either via the deprecated tag or via its replacement, the  tag.

Security
Recent developments in the coding of applications, including mobile and embedded systems, have led to the awareness of the security of applets.

Open platform applets
Applets in an open platform environment should provide secure interactions between different applications. A compositional approach can be used to provide security for open platform applets. Advanced compositional verification methods have been developed for secure applet interactions.

Java applets
A Java applet contains different security models: unsigned Java applet security, signed Java applet security, and self-signed Java applet security.

Web-based applets
In an applet-enabled web browser, many methods can be used to provide applet security for malicious applets. A malicious applet can infect a computer system in many ways, including denial of service, invasion of privacy, and annoyance. A typical solution for malicious applets is to make the web browser to monitor applets' activities. This will result in a web browser that will enable the manual or automatic stopping of malicious applets.

title: Applet