Glass is a non-crystalline transparent amorphous solid, that has widespread practical and decorative use in, for example, window panes and optics. Glass is most formed by rapid cooling of the molten form, some glasses such as volcanic glass are occurring; the most familiar, the oldest, types of manufactured glass are "silicate glasses" based on the chemical compound silica, the primary constituent of sand. Soda-lime glass, containing around 70% silica, account for around 90% of manufactured glass; the term glass, in popular usage, is used to refer only to this type of material, although silica-free glasses have desirable properties for applications in modern communications technology. Some objects, such as drinking glasses and eyeglasses, are so made of silicate-based glass that they are called by the name of the material. Although brittle, silicate glass is durable, many examples of glass fragments exist from early glass-making cultures. Archaeological evidence suggests glass-making dates back to at least 3,600 BCE in Mesopotamia, Egypt, or Syria.
The earliest known glass objects were beads created accidentally during metal-working or the production of faience. Due to its ease of formability into any shape, glass has been traditionally used for vessels: bowls, bottles and drinking glasses. In its most solid forms, it has been used for paperweights, marbles. Glass can be coloured by adding metal salts or painted and printed with vitreous enamels, leading to its use in stained glass windows and other glass art objects; the refractive and transmission properties of glass make glass suitable for manufacturing optical lenses and optoelectronics materials. Extruded glass fibres have application as optical fibres in communications networks, thermal insulating material when matted as glass wool so as to trap air, or in glass-fibre reinforced plastic; the standard definition of a glass is a solid formed by rapid melt quenching. However, the term "glass" is defined in a broader sense, to describe any non-crystalline solid that exhibits a glass transition when heated towards the liquid state.
Glass is an amorphous solid. Although the atomic-scale structure of glass shares characteristics of the structure of a supercooled liquid, glass exhibits all the mechanical properties of a solid; as in other amorphous solids, the atomic structure of a glass lacks the long-range periodicity observed in crystalline solids. Due to chemical bonding constraints, glasses do possess a high degree of short-range order with respect to local atomic polyhedra; the notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis. Laboratory measurements of room temperature glass flow do show a motion consistent with a material viscosity on the order of 1017–1018 Pa s. For melt quenching, if the cooling is sufficiently rapid crystallization is prevented and instead the disordered atomic configuration of the supercooled liquid is frozen into the solid state at Tg; the tendency for a material to form a glass while quenched is called glass-forming ability.
This ability can be predicted by the rigidity theory. A glass exists in a structurally metastable state with respect to its crystalline form, although in certain circumstances, for example in atactic polymers, there is no crystalline analogue of the amorphous phase. Glass is sometimes considered to be a liquid due to its lack of a first-order phase transition where certain thermodynamic variables such as volume and enthalpy are discontinuous through the glass transition range; the glass transition may be described as analogous to a second-order phase transition where the intensive thermodynamic variables such as the thermal expansivity and heat capacity are discontinuous. Nonetheless, the equilibrium theory of phase transformations does not hold for glass, hence the glass transition cannot be classed as one of the classical equilibrium phase transformations in solids. Glass can form from volcanic magma. Obsidian is a common volcanic glass with high silica content formed when felsic lava extruded from a volcano cools rapidly.
Impactite is a form of glass formed by the impact of a meteorite, where Moldavite, Libyan desert glass are notable examples. Vitrification of quartz can occur when lightning strikes sand, forming hollow, branching rootlike structures called fulgurites. Trinitite is a glassy residue formed from the desert floor sand at the Trinity nuclear bomb test site. Edeowie glass, found in South Australia, is proposed to originate from Pleistocene grassland fires, lightning strikes, or hypervelocity impact by one or several asteroids or comets. Occurring obsidian glass was used by Stone Age societies as it fractures along sharp edges, making it ideal for cutting tools and weapons. Archaeological evidence suggests that the first true synthetic glass was made in Lebanon and the coastal north Syria, Mesopotamia or ancient Egypt; the earliest known glass objects, of the mid third millennium BCE, were beads initially created as accidental by-products of metal-working or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.
InLiving is an educational game focusing on independent living. Aimed at young people aged 13–25, the game has been developed by Creative North Studios and Kirklees Neighbourhood Housing for use by housing organisations as a tool to deliver key information to prospective and current tenants; the game helps players understand the challenges they may face when moving into a property for the first time. The game was launched on 5 June 2008; the game was developed for mobile phones and supports over 500 different devices. A web-based version of the game is in development due for release late 2009; the game has had positive reception since its launch in June 2008 and was soon featured in Inside Housing in the'What Works' section. The InLiving project is supported as part of the Innovation Exchange programme. Several other games have been developed based on the InLiving Platform. Two such games are HouseM8 and StreetM8. InLiving Official Website
Abu'l-Barakāt Hibat Allah ibn Malkā al-Baghdādī was an Islamic philosopher and physicist of Jewish descent from Baghdad, Iraq. Abu'l-Barakāt, an older contemporary of Maimonides, was known by his Hebrew birth name Baruch ben Malka and was given the name of Nathanel by his pupil Isaac ben Ezra before his conversion from Judaism to Islam in his life, his writings include the anti-Aristotelian philosophical work Kitāb al-Muʿtabar. Abu'l-Barakāt was an Aristotelian philosopher who in many respects followed Ibn Sina, but developed his own ideas, he proposed an explanation of the acceleration of falling bodies by the accumulation of successive increments of power with successive increments of velocity. His thought influenced the Illuminationist school of classical Islamic philosophy, the medieval Jewish philosopher Ibn Kammuna, the medieval Christian philosophers Jean Buridan and Albert of Saxony. Abu'l-Barakāt, famed as Awḥad al-Zamān, was born in Balad, a town on the Tigris above Mosul in modern-day Iraq.
As a renowned physician, he served at the courts of the caliphs of the Seljuk sultans. He converted to Islam in his life. Abu'l Barakat does not refer to his conversion in his writings, the historical sources give contradictory episodes of his conversion. According to the various reports, he converted either out of "wounded pride", fear of the personal consequences of the death of Sultan Mahmud's wife while under his care as a physician or fear of execution when he was taken prisoner in a battle between the armies of the caliph and that of the sultan. Ayala Eliyahu argues that the conversion was "probably motivated by convenience reasons". Isaac, the son of the Abraham Ibn Ezra and the son-in-law of Judah Halevi, was one of his pupils, to whom Abu'l-Barakāt, Jewish at the time, dictated a long philosophical commentary on Ecclesiastes, written in Arabic using Hebrew aleph bet. Isaac wrote a poem in his honour as introduction to this work. Al-Baghdadi described an early scientific method emphasizing repeated experimentation, influenced by Ibn Sina, as follows: "Because of the frequency of the experience, these judgements may be regarded as certain without our knowing the reason.
For there is certain knowledge. It must accordingly be supposed that it is due to some modality thereof, thus the cause qua cause, though not its mode of operation, is known. For experimental science is constituted by a knowledge of the cause and by an induction based on all the data of sensation, but in the cases in which an experiment has not been completed, because of its not having been repeated in such a way that the persons, the time and the circumstances varied in everything that did not cause the determining cause, whereas this cause, the experiment does not prove certain knowledge, but only opinion." Al-Baghdadi was a follower of the philosophical teachings of Ibn Sina. According to Alistair Cameron Crombie, al-Baghdadi proposed an explanation of the acceleration of falling bodies by the accumulation of successive increments of power with successive increments of velocity. According to Shlomo Pines, al-Baghdadi's theory of motion was thus the oldest negation of Aristotle's fundamental dynamic law, anticipation in a vague fashion of the fundamental law of classical mechanics.
Al-Baghdadi's theory of motion distinguished between velocity and acceleration and showed that force is proportional to acceleration rather than velocity. The 14th-century philosophers Jean Buridan and Albert of Saxony refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus. Abu'l-Barakat modified Ibn Sina's theory of projectile motion, stated that the mover imparts a violent inclination on the moved and that this diminishes as the moving object distances itself from the mover. Al-Baghdadi suggested that motion is relative, writing that "there is motion only if the relative positions of the bodies in question change." He stated that "each type of body has a characteristic velocity that reaches its maximum when its motion encounters no resistance." Al-Baghdadi criticized Aristotle's concept of time as "the measure of motion" and instead redefines the concept with his own definition of time as "the measure of being", thus distinguishing between space and time, reclassifying time as a metaphysical concept rather than a physical one.
The scholar Y. Tzvi Langermann writes: Dissatisfied with the regnant approach, which treated time as an accident of the cosmos, al-Baghdadi drew the conclusion that time is an entity whose conception is a priori and as general as that of being, encompassing the sensible and the non-sensible, that which moves and that, at rest. Our idea of time results not from abstraction, stripping accidents from perceived objects, but from a mental representation based on an innate idea. Al-Baghdadi stops short of offering a precise definition of time, stating only that'were it to be said that time is the measure of being, that would be better than saying that it is the measure of motion', his reclassification of time as a subject for metaphysics rather than for physics represents