A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, conducts electricity and heat well. Metals are malleable or ductile. A metal may be an alloy such as stainless steel. In physics, a metal is regarded as any substance capable of conducting electricity at a temperature of absolute zero. Many elements and compounds that are not classified as metals become metallic under high pressures. For example, the nonmetal iodine becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure; some materials regarded as metals can become nonmetals. Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure. In chemistry, two elements that would otherwise qualify as brittle metals—arsenic and antimony—are instead recognised as metalloids, on account of their predominately non-metallic chemistry. Around 95 of the 118 elements in the periodic table are metals; the number is inexact as the boundaries between metals and metalloids fluctuate due to a lack of universally accepted definitions of the categories involved.
In astrophysics the term "metal" is cast more to refer to all chemical elements in a star that are heavier than the lightest two and helium, not just traditional metals. A star fuses lighter atoms hydrogen and helium, into heavier atoms over its lifetime. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements. Metals are present in many aspects of modern life; the strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools and railroad tracks. Precious metals were used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements; the history of metals is thought to begin with the use of copper about 11,000 years ago. Gold, iron and brass were in use before the first known appearance of bronze in the 5th millennium BCE. Subsequent developments include the production of early forms of steel.
Metals are lustrous, at least when freshly prepared, polished, or fractured. Sheets of metal thicker than a few micrometres appear opaque; the solid or liquid state of metals originates in the capacity of the metal atoms involved to lose their outer shell electrons. Broadly, the forces holding an individual atom’s outer shell electrons in place are weaker than the attractive forces on the same electrons arising from interactions between the atoms in the solid or liquid metal; the electrons involved become delocalised and the atomic structure of a metal can be visualised as a collection of atoms embedded in a cloud of mobile electrons. This type of interaction is called a metallic bond; the strength of metallic bonds for different elemental metals reaches a maximum around the center of the transition metal series, as these elements have large numbers of delocalized electrons. Although most elemental metals have higher densities than most nonmetals, there is a wide variation in their densities, lithium being the least dense and osmium the most dense.
Magnesium and titanium are light metals of significant commercial importance. Their respective densities of 1.7, 2.7 and 4.5 g/cm3 can be compared to those of the older structural metals, like iron at 7.9 and copper at 8.9 g/cm3. An iron ball would thus weigh about as much as three aluminium balls. Metals are malleable and ductile, deforming under stress without cleaving; the nondirectional nature of metallic bonding is thought to contribute to the ductility of most metallic solids. In contrast, in an ionic compound like table salt, when the planes of an ionic bond slide past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal; such a shift is not observed in a covalently bonded crystal, such as a diamond, where fracture and crystal fragmentation occurs. Reversible elastic deformation in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain. Heat or forces larger than a metal's elastic limit may cause a permanent deformation, known as plastic deformation or plasticity.
An applied force may be a compressive force, or a shear, bending or torsion force. A temperature change may affect the movement or displacement of structural defects in the metal such as grain boundaries, point vacancies and screw dislocations, stacking faults and twins in both crystalline and non-crystalline metals. Internal slip and metal fatigue may ensue; the atoms of metallic substances are arranged in one of three common crystal structures, namely body-centered cubic, face-centered cubic, hexagonal close-packed. In bcc, each atom is positioned at the center of a cube of eight others. In fcc and hcp, each atom is surrounded by twelve others; some metals adopt different structures depending on the temperature. The
Aqua regia is a mixture of nitric acid and hydrochloric acid, optimally in a molar ratio of 1:3. Aqua regia is a yellow-orange fuming liquid, so named by alchemists because it can dissolve the noble metals gold and platinum, though not all metals. Aqua regia is used to produce chloroauric acid, the electrolyte in the Wohlwill process for refining the highest quality gold. Aqua regia is used in etching and in specific analytic procedures, it is used in some laboratories to clean glassware of organic compounds and metal particles. This method is preferred over the more traditional chromic acid bath for cleaning NMR tubes, because no traces of paramagnetic chromium can remain to spoil spectra. While chromic acid baths are discouraged because of the high toxicity of chromium and the potential for explosions, aqua regia is itself corrosive and has been implicated in several explosions due to mishandling. Due to the reaction between its components resulting in its decomposition, aqua regia loses its effectiveness, so its components are only mixed before use.
While local regulations may vary, aqua regia may be disposed of by careful neutralization, before being poured down the sink. If there is contamination by dissolved metals, the neutralized solution should be collected for disposal. Aqua regia dissolves gold, though neither constituent acid will do so alone, because, in combination, each acid performs a different task. Nitric acid is a powerful oxidizer, which will dissolve a undetectable amount of gold, forming gold ions; the hydrochloric acid provides a ready supply of chloride ions, which react with the gold ions to produce tetrachloroaurate anions in solution. The reaction with hydrochloric acid is an equilibrium reaction that favors formation of chloroaurate anions; this results in a removal of gold ions from solution and allows further oxidation of gold to take place. The gold dissolves to become chloroauric acid. In addition, gold may be dissolved by the chlorine present in aqua regia. Appropriate equations are: Au + 3 HNO3 + 4 HCl ↽ − ⇀ − + 3 + + + 2 H2OorAu + HNO3 + 4 HCl ↽ − ⇀ − + + + + H2OIf the aqua regia solution only contains gold, solid tetrachloroauric acid may be prepared by boiling off excess aqua regia, removing residual nitric acid by heating with hydrochloric acid.
That step reduces nitric acid. If elemental gold is desired, it may be selectively reduced with sulfur dioxide, oxalic acid, etc; the equation for the reduction of gold by sulfur dioxide is: 2 AuCl−4 + 3 SO2 + 6 H2O → 2 Au + 12 H+ + 3 SO2−4 + 8 Cl−. Similar equations can be written for platinum; as with gold, the oxidation reaction can be written with either nitric oxide or nitrogen dioxide as the nitrogen oxide product. Pt + 4 NO−3 + 8 H+ → Pt4+ + 4 NO2 + 4 H2O 3Pt + 4 NO−3 + 16 H+ → 3Pt4+ + 4 NO + 8 H2O The oxidized platinum ion reacts with chloride ions resulting in the chloroplatinate ion. Pt4+ + 6 Cl− → PtCl2−6 Experimental evidence reveals that the reaction of platinum with aqua regia is more complex; the initial reactions produce a mixture of nitrosoplatinic chloride. The nitrosoplatinic chloride is a solid product. If full dissolution of the platinum is desired, repeated extractions of the residual solids with concentrated hydrochloric acid must be performed. 2Pt + 2HNO3 + 8 HCl → 2PtCl4 + H2PtCl4 + 4 H2O 2PtCl4 + 2 HCl ⇌ H2PtCl4 + 2 NOCl The chloroplatinous acid can be oxidized to chloroplatinic acid by saturating the solution with chlorine while heating.
H2PtCl4 + Cl2 → H2PtCl6 Dissolving platinum solids in aqua regia was the mode of discovery for the most dense metals and osmium, both of which are found in platinum ore and will not be dissolved by the acid, instead collecting on the base of the vessel. As a practical matter, when platinum group metals are purified through dissolution in aqua regia, gold is precipitated by treatment with iron chloride. Platinum in the filtrate, as hexachloroplatinate, is converted to ammonium hexachloroplatinate by the addition of ammonium chloride; this ammonium salt is insoluble, it can be filtered off. Ignition converts it to platinum metal: 3 2PtCl6 → 3 Pt + 2 N2 + 2 NH4Cl + 16 HClUnprecipitated hexachloroplatinate is reduced with elemental zinc, a similar method is suitable for small scale recovery of platinum from laboratory residues. Aqua regia reacts with tin to form tin chloride, containing tin in its highest oxidation state: 4 HCl + 2 HNO3 + Sn → SnCl4 + NO2 + NO + 3 H2O Upon mixing of concentrated hydrochloric acid and concentrated nitric acid, chemical reactions occur.
These reactions result in the volatile products nitrosyl chloride and chlorine as evidenced by the fuming nature and characteristic yellow color of aqua regia. As the volatile products escape from solution, the aqua regia loses its potency. HNO3 + 3 HCl → NOCl + Cl2 + 2 H2O Nitrosyl chloride can further decompose into nitric oxide and chlorine; this dissociation is equilibrium-limited. Therefore, in addition to nitrosyl chloride and chlorine, the fumes over aqua regia contain nitric oxide. 2 NOCl → 2 NO + Cl2 Because nitric oxide reacts wi
Carbon is a chemical element with symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds, it belongs to group 14 of the periodic table. Three isotopes occur 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in the Earth's crust, the fourth most abundant element in the universe by mass after hydrogen and oxygen. Carbon's abundance, its unique diversity of organic compounds, its unusual ability to form polymers at the temperatures encountered on Earth enables this element to serve as a common element of all known life, it is the second most abundant element in the human body by mass after oxygen. The atoms of carbon can bond together in different ways, termed allotropes of carbon; the best known are graphite and amorphous carbon. The physical properties of carbon vary with the allotropic form.
For example, graphite is opaque and black while diamond is transparent. Graphite is soft enough to form a streak on paper, while diamond is the hardest occurring material known. Graphite is a good electrical conductor. Under normal conditions, carbon nanotubes, graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure, they are chemically resistant and require high temperature to react with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes; the largest sources of inorganic carbon are limestones and carbon dioxide, but significant quantities occur in organic deposits of coal, peat and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with ten million compounds described to date, yet that number is but a fraction of the number of theoretically possible compounds under standard conditions.
For this reason, carbon has been referred to as the "king of the elements". The allotropes of carbon include graphite, one of the softest known substances, diamond, the hardest occurring substance, it bonds with other small atoms, including other carbon atoms, is capable of forming multiple stable covalent bonds with suitable multivalent atoms. Carbon is known to form ten million different compounds, a large majority of all chemical compounds. Carbon has the highest sublimation point of all elements. At atmospheric pressure it has no melting point, as its triple point is at 10.8±0.2 MPa and 4,600 ± 300 K, so it sublimes at about 3,900 K. Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised pi system is much more vulnerable to attack. For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C66, which preserves the hexagonal units of graphite while breaking up the larger structure.
Carbon sublimes in a carbon arc, which has a temperature of about 5800 K. Thus, irrespective of its allotropic form, carbon remains solid at higher temperatures than the highest-melting-point metals such as tungsten or rhenium. Although thermodynamically prone to oxidation, carbon resists oxidation more than elements such as iron and copper, which are weaker reducing agents at room temperature. Carbon is the sixth element, with a ground-state electron configuration of 1s22s22p2, of which the four outer electrons are valence electrons, its first four ionisation energies, 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, are much higher than those of the heavier group-14 elements. The electronegativity of carbon is 2.5 higher than the heavier group-14 elements, but close to most of the nearby nonmetals, as well as some of the second- and third-row transition metals. Carbon's covalent radii are taken as 77.2 pm, 66.7 pm and 60.3 pm, although these may vary depending on coordination number and what the carbon is bonded to.
In general, covalent radius decreases with higher bond order. Carbon compounds form the basis of all known life on Earth, the carbon–nitrogen cycle provides some of the energy produced by the Sun and other stars. Although it forms an extraordinary variety of compounds, most forms of carbon are comparatively unreactive under normal conditions. At standard temperature and pressure, it resists all but the strongest oxidizers, it does not react with hydrochloric acid, chlorine or any alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon oxides and will rob oxygen from metal oxides to leave the elemental metal; this exothermic reaction is used in the iron and steel industry to smelt iron and to control the carbon content of steel: Fe3O4 + 4 C → 3 Fe + 4 COCarbon monoxide can be recycled to smelt more iron: Fe3O4 + 4 CO → 3 Fe + 4 CO2with sulfur to form carbon disulfide and with steam in the coal-gas reaction: C + H2O → CO + H2. Carbon combines with some metals at high temperatures to form metallic carbides, such as the iron carbide cementite in steel and tungsten carbide used as an abrasive and for making hard tips for cutting tools.
The system of carbon allotropes spans a range of extremes: Atomic carbon is a ver
University of Cambridge
The University of Cambridge is a collegiate public research university in Cambridge, United Kingdom. Founded in 1209 and granted a Royal Charter by King Henry III in 1231, Cambridge is the second-oldest university in the English-speaking world and the world's fourth-oldest surviving university; the university grew out of an association of scholars who left the University of Oxford after a dispute with the townspeople. The two'ancient universities' share many common features and are referred to jointly as'Oxbridge'; the history and influence of the University of Cambridge has made it one of the most prestigious universities in the world. Cambridge is formed from a variety of institutions which include 31 constituent Colleges and over 100 academic departments organised into six schools. Cambridge University Press, a department of the university, is the world's oldest publishing house and the second-largest university press in the world; the university operates eight cultural and scientific museums, including the Fitzwilliam Museum, as well as a botanic garden.
Cambridge's libraries hold a total of around 15 million books, eight million of which are in Cambridge University Library, a legal deposit library. In the fiscal year ending 31 July 2018, the university had a total income of £1.965 billion, of which £515.5 million was from research grants and contracts. In the financial year ending 2017, the central university and colleges had combined net assets of around £11.8 billion, the largest of any university in the country. However, the true extent of Cambridge's wealth is much higher as many colleges hold their historic main sites, which date as far back as the 13th century, at depreceated valuations. Furthermore, many of the wealthiest colleges do not account for “heritage assets” such as works of art, libraries or artefacts, whose value many college accounts describe as “immaterial”; the university is linked with the development of the high-tech business cluster known as'Silicon Fen'. It is a member of numerous associations and forms part of the'golden triangle' of English universities and Cambridge University Health Partners, an academic health science centre.
As of 2018, Cambridge is the top-ranked university in the United Kingdom according to all major league tables. As of September 2017, Cambridge is ranked the world's second best university by the Times Higher Education World University Rankings, is ranked 3rd worldwide by Academic Ranking of World Universities, 6th by QS, 7th by US News. According to the Times Higher Education ranking, no other institution in the world ranks in the top 10 for as many subjects; the university has educated many notable alumni, including eminent mathematicians, politicians, philosophers, writers and foreign Heads of State. As of March 2019, 118 Nobel Laureates, 11 Fields Medalists, 7 Turing Award winners and 15 British Prime Ministers have been affiliated with Cambridge as students, faculty or research staff. By the late 12th century, the Cambridge area had a scholarly and ecclesiastical reputation, due to monks from the nearby bishopric church of Ely. However, it was an incident at Oxford, most to have led to the establishment of the university: two Oxford scholars were hanged by the town authorities for the death of a woman, without consulting the ecclesiastical authorities, who would take precedence in such a case, but were at that time in conflict with King John.
The University of Oxford went into suspension in protest, most scholars moved to cities such as Paris and Cambridge. After the University of Oxford reformed several years enough scholars remained in Cambridge to form the nucleus of the new university. In order to claim precedence, it is common for Cambridge to trace its founding to the 1231 charter from King Henry III granting it the right to discipline its own members and an exemption from some taxes. A bull in 1233 from Pope Gregory IX gave graduates from Cambridge the right to teach "everywhere in Christendom". After Cambridge was described as a studium generale in a letter from Pope Nicholas IV in 1290, confirmed as such in a bull by Pope John XXII in 1318, it became common for researchers from other European medieval universities to visit Cambridge to study or to give lecture courses; the colleges at the University of Cambridge were an incidental feature of the system. No college is as old as the university itself; the colleges were endowed fellowships of scholars.
There were institutions without endowments, called hostels. The hostels were absorbed by the colleges over the centuries, but they have left some traces, such as the name of Garret Hostel Lane. Hugh Balsham, Bishop of Ely, founded Peterhouse, Cambridge's first college, in 1284. Many colleges were founded during the 14th and 15th centuries, but colleges continued to be established until modern times, although there was a gap of 204 years between the founding of Sidney Sussex in 1596 and that of Downing in 1800; the most established college is Robinson, built in the late 1970s. However, Homerton College only achieved full university college status in March 2010, making it the newest full college. In medieval times, many colleges were founded so that their members would pray for the souls of the founders, were associated with chapels or abbeys; the colleges' focus changed in 1536 with the Dissolution of the Monasteries. King Henry VIII ordered the university to disband its Faculty of Canon Law and to stop teaching "scholastic philosophy".
In response, colleges changed
Silicon is a chemical element with symbol Si and atomic number 14. It is a brittle crystalline solid with a blue-grey metallic lustre, it is a member of group 14 in the periodic table: carbon is above it. It is unreactive; because of its high chemical affinity for oxygen, it was not until 1823 that Jöns Jakob Berzelius was first able to prepare it and characterize it in pure form. Its melting and boiling points of 1414 °C and 3265 °C are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but rarely occurs as the pure element in the Earth's crust, it is most distributed in dusts, sands and planets as various forms of silicon dioxide or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust after oxygen. Most silicon is used commercially without being separated, with little processing of the natural minerals.
Such use includes industrial construction with clays, silica sand, stone. Silicates are used in Portland cement for mortar and stucco, mixed with silica sand and gravel to make concrete for walkways and roads, they are used in whiteware ceramics such as porcelain, in traditional quartz-based soda-lime glass and many other specialty glasses. Silicon compounds such as silicon carbide are used as abrasives and components of high-strength ceramics. Silicon is the basis of the used synthetic polymers called silicones. Elemental silicon has a large impact on the modern world economy. Most free silicon is used in the steel refining, aluminium-casting, fine chemical industries. More visibly, the small portion of highly purified elemental silicon used in semiconductor electronics is essential to integrated circuits – most computers, cell phones, modern technology depend on it. Silicon is an essential element in biology. However, various sea sponges and microorganisms, such as diatoms and radiolaria, secrete skeletal structures made of silica.
Silica is deposited in many plant tissues. In 1787 Antoine Lavoisier suspected that silica might be an oxide of a fundamental chemical element, but the chemical affinity of silicon for oxygen is high enough that he had no means to reduce the oxide and isolate the element. After an attempt to isolate silicon in 1808, Sir Humphry Davy proposed the name "silicium" for silicon, from the Latin silex, silicis for flint, adding the "-ium" ending because he believed it to be a metal. Most other languages use transliterated forms of Davy's name, sometimes adapted to local phonology. A few others use instead a calque of the Latin root. Gay-Lussac and Thénard are thought to have prepared impure amorphous silicon in 1811, through the heating of isolated potassium metal with silicon tetrafluoride, but they did not purify and characterize the product, nor identify it as a new element. Silicon was given its present name in 1817 by Scottish chemist Thomas Thomson, he retained part of Davy's name but added "-on" because he believed that silicon was a nonmetal similar to boron and carbon.
In 1823, Jöns Jacob Berzelius prepared amorphous silicon using the same method as Gay-Lussac, but purifying the product to a brown powder by washing it. As a result, he is given credit for the element's discovery; the same year, Berzelius became the first to prepare silicon tetrachloride. Silicon in its more common crystalline form was not prepared until 31 years by Deville. By electrolyzing a mixture of sodium chloride and aluminium chloride containing 10% silicon, he was able to obtain a impure allotrope of silicon in 1854. More cost-effective methods have been developed to isolate several allotrope forms, the most recent being silicene in 2010. Meanwhile, research on the chemistry of silicon continued; the first organosilicon compound, was synthesised by Charles Friedel and James Crafts in 1863, but detailed characterisation of organosilicon chemistry was only done in the early 20th century by Frederic Kipping. Starting in the 1920s, the work of William Lawrence Bragg on X-ray crystallography elucidated the compositions of the silicates, known from analytical chemistry but had not yet been understood, together with Linus Pauling's development of crystal chemistry and Victor Goldschmidt's development of geochemistry.
The middle of the 20th century saw the development of the chemistry and industrial use of siloxanes and the growing use of silicone polymers and resins. In the late 20th century, the complexity of the crystal chemistry of silicides was mapped, along with the solid-state chemistry of doped semiconductors; because silicon is an important element in high-technology semiconductor devi
YouTube is an American video-sharing website headquartered in San Bruno, California. Three former PayPal employees—Chad Hurley, Steve Chen, Jawed Karim—created the service in February 2005. Google bought the site in November 2006 for US$1.65 billion. YouTube allows users to upload, rate, add to playlists, comment on videos, subscribe to other users, it offers a wide variety of corporate media videos. Available content includes video clips, TV show clips, music videos and documentary films, audio recordings, movie trailers, live streams, other content such as video blogging, short original videos, educational videos. Most of the content on YouTube is uploaded by individuals, but media corporations including CBS, the BBC, Hulu offer some of their material via YouTube as part of the YouTube partnership program. Unregistered users can only watch videos on the site, while registered users are permitted to upload an unlimited number of videos and add comments to videos. Videos deemed inappropriate are available only to registered users affirming themselves to be at least 18 years old.
YouTube and its creators earn advertising revenue from Google AdSense, a program which targets ads according to site content and audience. The vast majority of its videos are free to view, but there are exceptions, including subscription-based premium channels, film rentals, as well as YouTube Music and YouTube Premium, subscription services offering premium and ad-free music streaming, ad-free access to all content, including exclusive content commissioned from notable personalities; as of February 2017, there were more than 400 hours of content uploaded to YouTube each minute, one billion hours of content being watched on YouTube every day. As of August 2018, the website is ranked as the second-most popular site in the world, according to Alexa Internet. YouTube has faced criticism over aspects of its operations, including its handling of copyrighted content contained within uploaded videos, its recommendation algorithms perpetuating videos that promote conspiracy theories and falsehoods, hosting videos ostensibly targeting children but containing violent and/or sexually suggestive content involving popular characters, videos of minors attracting pedophilic activities in their comment sections, fluctuating policies on the types of content, eligible to be monetized with advertising.
YouTube was founded by Chad Hurley, Steve Chen, Jawed Karim, who were all early employees of PayPal. Hurley had studied design at Indiana University of Pennsylvania, Chen and Karim studied computer science together at the University of Illinois at Urbana–Champaign. According to a story, repeated in the media and Chen developed the idea for YouTube during the early months of 2005, after they had experienced difficulty sharing videos, shot at a dinner party at Chen's apartment in San Francisco. Karim did not attend the party and denied that it had occurred, but Chen commented that the idea that YouTube was founded after a dinner party "was very strengthened by marketing ideas around creating a story, digestible". Karim said the inspiration for YouTube first came from Janet Jackson's role in the 2004 Super Bowl incident, when her breast was exposed during her performance, from the 2004 Indian Ocean tsunami. Karim could not find video clips of either event online, which led to the idea of a video sharing site.
Hurley and Chen said that the original idea for YouTube was a video version of an online dating service, had been influenced by the website Hot or Not. Difficulty in finding enough dating videos led to a change of plans, with the site's founders deciding to accept uploads of any type of video. YouTube began as a venture capital-funded technology startup from an $11.5 million investment by Sequoia Capital and an $8 million investment from Artis Capital Management between November 2005 and April 2006. YouTube's early headquarters were situated above a pizzeria and Japanese restaurant in San Mateo, California; the domain name www.youtube.com was activated on February 14, 2005, the website was developed over the subsequent months. The first YouTube video, titled Me at the zoo, shows co-founder Jawed Karim at the San Diego Zoo; the video was uploaded on April 23, 2005, can still be viewed on the site. YouTube offered the public a beta test of the site in May 2005; the first video to reach one million views was a Nike advertisement featuring Ronaldinho in November 2005.
Following a $3.5 million investment from Sequoia Capital in November, the site launched on December 15, 2005, by which time the site was receiving 8 million views a day. The site grew and, in July 2006, the company announced that more than 65,000 new videos were being uploaded every day, that the site was receiving 100 million video views per day. According to data published by market research company comScore, YouTube is the dominant provider of online video in the United States, with a market share of around 43% and more than 14 billion views of videos in May 2010. In May 2011, 48 hours of new videos were uploaded to the site every minute, which increased to 60 hours every minute in January 2012, 100 hours every minute in May 2013, 300 hours every minute in November 2014, 400 hours every minute in February 2017; as of January 2012, the site had 800 million unique users a month. It is estimated that in 2007 YouTube consumed as much bandwidth as the entire Internet in 2000. According to third-party web analytics providers and SimilarWeb, YouTube is the second-most visited website in the world, as of December 2016.
Thermodynamics is the branch of physics that deals with heat and temperature, their relation to energy, work and properties of bodies of matter. The behavior of these quantities is governed by the four laws of thermodynamics, irrespective of the specific composition of the material or system in question; the laws of thermodynamics are explained in terms of microscopic constituents by statistical mechanics. Thermodynamics applies to a wide variety of topics in science and engineering physical chemistry, chemical engineering and mechanical engineering. Thermodynamics developed out of a desire to increase the efficiency of early steam engines through the work of French physicist Nicolas Léonard Sadi Carnot who believed that engine efficiency was the key that could help France win the Napoleonic Wars. Scots-Irish physicist Lord Kelvin was the first to formulate a concise definition of thermodynamics in 1854 which stated, "Thermo-dynamics is the subject of the relation of heat to forces acting between contiguous parts of bodies, the relation of heat to electrical agency."
The initial application of thermodynamics to mechanical heat engines was extended early on to the study of chemical compounds and chemical reactions. Chemical thermodynamics studies the nature of the role of entropy in the process of chemical reactions and has provided the bulk of expansion and knowledge of the field. Other formulations of thermodynamics emerged in the following decades. Statistical thermodynamics, or statistical mechanics, concerned itself with statistical predictions of the collective motion of particles from their microscopic behavior. In 1909, Constantin Carathéodory presented a purely mathematical approach to the field in his axiomatic formulation of thermodynamics, a description referred to as geometrical thermodynamics. A description of any thermodynamic system employs the four laws of thermodynamics that form an axiomatic basis; the first law specifies that energy can be exchanged between physical systems as work. The second law defines the existence of a quantity called entropy, that describes the direction, thermodynamically, that a system can evolve and quantifies the state of order of a system and that can be used to quantify the useful work that can be extracted from the system.
In thermodynamics, interactions between large ensembles of objects are categorized. Central to this are the concepts of its surroundings. A system is composed of particles, whose average motions define its properties, those properties are in turn related to one another through equations of state. Properties can be combined to express internal energy and thermodynamic potentials, which are useful for determining conditions for equilibrium and spontaneous processes. With these tools, thermodynamics can be used to describe how systems respond to changes in their environment; this can be applied to a wide variety of topics in science and engineering, such as engines, phase transitions, chemical reactions, transport phenomena, black holes. The results of thermodynamics are essential for other fields of physics and for chemistry, chemical engineering, corrosion engineering, aerospace engineering, mechanical engineering, cell biology, biomedical engineering, materials science, economics, to name a few.
This article is focused on classical thermodynamics which studies systems in thermodynamic equilibrium. Non-equilibrium thermodynamics is treated as an extension of the classical treatment, but statistical mechanics has brought many advances to that field; the history of thermodynamics as a scientific discipline begins with Otto von Guericke who, in 1650, built and designed the world's first vacuum pump and demonstrated a vacuum using his Magdeburg hemispheres. Guericke was driven to make a vacuum in order to disprove Aristotle's long-held supposition that'nature abhors a vacuum'. Shortly after Guericke, the English physicist and chemist Robert Boyle had learned of Guericke's designs and, in 1656, in coordination with English scientist Robert Hooke, built an air pump. Using this pump and Hooke noticed a correlation between pressure and volume. In time, Boyle's Law was formulated, which states that pressure and volume are inversely proportional. In 1679, based on these concepts, an associate of Boyle's named Denis Papin built a steam digester, a closed vessel with a fitting lid that confined steam until a high pressure was generated.
Designs implemented a steam release valve that kept the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and a cylinder engine, he did not, follow through with his design. In 1697, based on Papin's designs, engineer Thomas Savery built the first engine, followed by Thomas Newcomen in 1712. Although these early engines were crude and inefficient, they attracted the attention of the leading scientists of the time; the fundamental concepts of heat capacity and latent heat, which were necessary for the development of thermodynamics, were developed by Professor Joseph Black at the University of Glasgow, where James Watt was employed as an instrument maker. Black and Watt performed experiments together, but it was Watt who conceived the idea of the external condenser which resulted in a large increase in steam engine efficiency. Drawing on all the previous work led Sadi Carnot, the "father of thermodynamics", to publish Reflections on the Motive Power of Fire, a discourse on heat, power and engine efficiency.
The book outlined the basic energetic relations between the Carnot engine, the Carnot cycle, motive power. It marked the start of thermodynamics as a modern scien