Hydraulics is a technology and applied science using engineering and other sciences involving the mechanical properties and use of liquids. At a basic level, hydraulics is the liquid counterpart of pneumatics, which concerns gases. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the applied engineering using the properties of fluids. In its fluid power applications, hydraulics is used for the generation and transmission of power by the use of pressurized liquids. Hydraulic topics range through some parts of science and most of engineering modules, cover concepts such as pipe flow, dam design and fluid control circuitry; the principles of hydraulics are in use in the human body within the vascular system and erectile tissue. Free surface hydraulics is the branch of hydraulics dealing with free surface flow, such as occurring in rivers, lakes and seas, its sub-field open-channel flow studies the flow in open channels. The word "hydraulics" originates from the Greek word ὑδραυλικός which in turn originates from ὕδωρ and αὐλός.
Early uses of water power date back to Mesopotamia and ancient Egypt, where irrigation has been used since the 6th millennium BC and water clocks had been used since the early 2nd millennium BC. Other early examples of water power include the Qanat system in ancient Persia and the Turpan water system in ancient Central Asia; the Greeks constructed sophisticated water and hydraulic power systems. An example is the construction by Eupalinos, under a public contract, of a watering channel for Samos, the Tunnel of Eupalinos. An early example of the usage of hydraulic wheel the earliest in Europe, is the Perachora wheel; the construction of the first hydraulic automata by Ctesibius and Hero of Alexandria is notable. Hero describes a number of working machines using hydraulic power, such as the force pump, known from many Roman sites as having been used for raising water and in fire engines; the Persians constructed an intricate system of water mills and dams known as the Shushtar Historical Hydraulic System.
The project, commenced by Achaemenid king Darius the Great and finished by a group of Roman engineers captured by Sassanian king Shapur I, has been referred to by UNESCO as "a masterpiece of creative genius." They were the inventors of the Qanat, an underground aqueduct. Several of Iran's large, ancient gardens were irrigated thanks to Qanats. In ancient China there was Sunshu Ao, Ximen Bao, Du Shi, Zhang Heng, Ma Jun, while medieval China had Su Song and Shen Kuo. Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation. In ancient Sri Lanka, hydraulics were used in the ancient kingdoms of Anuradhapura and Polonnaruwa; the discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to ingenuity more than 2,000 years ago. By the first century AD, several large-scale irrigation works had been completed.
Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control and recreational water courses and retaining structures and cooling systems were in place in Sigiriya, Sri Lanka. The coral on the massive rock at the site includes cisterns for collecting water. Large ancient reservoirs of Sri Lanka are Kalawewa, Parakrama Samudra, Tisa Wewa, Minneriya In Ancient Rome, many different hydraulic applications were developed, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining, they were among the first to make use of the siphon to carry water across valleys, used hushing on a large scale to prospect for and extract metal ores. They used lead in plumbing systems for domestic and public supply, such as feeding thermae. Hydraulic mining was used in the gold-fields of northern Spain, conquered by Augustus in 25 BC; the alluvial gold-mine of Las Medulas was one of the largest of their mines. It was worked by at least 7 long aqueducts, the water streams were used to erode the soft deposits, wash the tailings for the valuable gold content.
In 1619 Benedetto Castelli, a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e. management of rivers in the Papal States, beginning in 1626. Blaise Pascal studied fluid hydrodynamics and hydrostatics, centered on the principles of hydraulic fluids, his discovery on the theory behind hydraulics led to the invention of the hydraulic press by Joseph Bramah, which multiplied a smaller force acting on a smaller area into the application of a larger force totaled over a larger area, transmitted through the same pressure at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force.
This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the containe
A muzzle-loading rifle is a muzzle-loaded small arm or artillery piece that has a rifled barrel rather than a smoothbore. The term "rifled muzzle loader" is used to describe a type of artillery piece, although it is technically accurate for small arms as well. A shoulder arm is just called a "rifle", as all small arms were rifled by the time breechloading became prevalent. Muzzle and breechloading artillery served together for several decades, making a clear distinction more important. In the case of artillery, the abbreviation "RML" is prefixed to the guns designation. A muzzle loading weapon is loaded through the front of the barrel; this is the opposite of a breech-loading weapon or rifled breechloader, loaded from the breech-end of the barrel. The rifling grooves cut on the inside of the barrel cause the projectile to spin in flight, giving it greater stability and hence range and accuracy than smoothbore guns. Hand held rifles were well-developed by the 1740s. A popularly recognizable form of the "muzzleloader" is the Kentucky Rifle, developed in Pennsylvania.
The American Longrifle evolved from the German "Jäger" rifle. Like most early firearms, the first rifles were muzzle-loading, although this involved a lot of complication in inserting the bullet past the rifling, clogging and cleaning problems were notorious. There are muzzle-loading pistols and shotguns; the Minié ball of the middle 19th century increased the rate of fire of rifles to match that of smoothbores, rifled muzzle-loading small arms were adopted. These have given way to firearms that use alternative methods of inserting a projectile into the chamber via the breech; the La Hitte rifled. These guns were a considerable improvement over the previous smooth-bore guns, in use, they were able to shoot at 3,000 meters either ball-loaded shells or grapeshot. They appear to have been the first case of usage of rifled cannons on a battlefield; the muzzle-loading rifle was introduced into service in ships of the Royal Navy, after experimentation with alternative armament systems, after the failure of the Armstrong 100-pounder breech-loaders installed in 1860.
Until the middle of the 19th century Royal Navy warships had been armed with progressively larger smoothbore muzzle-loading cannon. These had by approached their limit in terms of armour penetration and destructive power, it was known that rifled ordnance provided more accuracy, a greater range and more penetrative power, the rationale behind the development and on-board shipping of the breech-loading cannon developed by the company owned by Sir William Armstrong. These weapons, were dangerously prone to failure explosively, an alternative armament became urgently necessary. An initial attempt at an alternative was the 100-pounder smoothbore Somerset cannon, while it was an improvement over previous smoothbore guns of lesser calibre, could not penetrate armour of thicknesses being shipped by British or foreign battleships; the type of gun adopted was a muzzle-loading weapon which fired projectiles with external studs which engaged with the rifling. This system was the "Woolwich" system. Furthermore, the muzzle velocity obtainable in these guns was no more than half of that obtained in interrupted screw breeched guns of the following century.
There were several reasons for this: the shell could not be made to fit too into the bore of the gun, as it would not have been possible to ram it home. Rifled muzzle loader are artillery pieces of muzzle-loading rifle format, invented in the mid-19th century. In contrast to smooth bore cannon which preceded it, the rifling of the gun barrel allowed much greater accuracy and penetration as the spin induced to the shell gave it directional stability. Typical guns weighed 30 tonnes with 10" diameter muzzles, were installed in forts and ships; this new gun and the rifled breech loader generated a huge arms race in the late 19th century, with rapid advances in fortifications and ironclad warships. In the British navy, many smaller 64-pounder smoothbore guns were converted to rifled weapons: the converted guns were called RMLs, whilst weapons manufactured with rifling were termed muzzle-loading rifles; this distinction did not survive with the larger calibres, which were all called RMLs. Many artillery pieces were converted from older smooth bore weapons once technical problems in strengthening the original cast iron body had been overcome.
The adopted solution, invented in 1863 by William Palliser, consisted of enlarging the bore to accept a wrought iron tube into which the rifling had been cut. The A tube was closed at the breech end by a wrought iron cup screwed into it. Iron was removed from the outside of the original gun barrel near to the muzzle so that a cast iron collar could be screwed over it and provide a shoulder at the muzzle to hold the A tube i
A projectile is any object thrown into space by the exertion of a force. Although any object in motion through space may be called a projectile, the term more refers to a ranged weapon. Mathematical equations of motion are used to analyze projectile trajectory. An object projected at an angle to the horizontal has both the vertical and horizontal components of velocity; the vertical component of the velocity on the y-axis given as Vy=USin while the horizontal component of the velocity Vx=UCos. There are various terms used in projectiles at specific angle teta 1. Time to reach maximum height, it is symbolized as, the time taken for the projectile to reach the maximum height from the plane of projection. Mathematically, it is give as t=USin/g Where g=acceleration due to gravity U= initial velocity teta= angle made by the projectile with the horizontal axis. 2. Time of flight: this is the total time taken for the projectile to fall back to the same plane from which it was projected. Mathematically it is given as T=2USin/g 3.
Maximum Height: this is the maximum height attained by the projectile OR the maximum displacement on the vertical axis covered by the projectile. It is given as H= U²Sin²/2g 4. Range: The Range of a projectile is the horizontal distance covered by the projectile. Mathematically, R= U²Sin2/g; the Range is maximum when angle teta= 45° I.e Sin2=1. Blowguns and pneumatic rifles use compressed gases, while most other guns and cannons utilize expanding gases liberated by sudden chemical reactions. Light-gas guns use a combination of these mechanisms. Railguns utilize electromagnetic fields to provide a constant acceleration along the entire length of the device increasing the muzzle velocity; some projectiles provide propulsion during flight by means of a rocket jet engine. In military terminology, a rocket is unguided. Note the two meanings of "rocket": an ICBM is a guided missile with a rocket engine. An explosion, whether or not by a weapon, causes the debris to act as multiple high velocity projectiles.
An explosive weapon, or device may be designed to produce many high velocity projectiles by the break-up of its casing, these are termed fragments. Many projectiles, e.g. shells, may carry an explosive charge or another chemical or biological substance. Aside from explosive payload, a projectile can be designed to cause special damage, e.g. fire, or poisoning. In projectile motion the most important force applied to the ‘projectile’ is the propelling force, in this case the propelling forces are the muscles that act upon the ball to make it move, the stronger the force applied, the more propelling force, which means the projectile will travel farther. See pitching, bowling. A projectile that does not contain an explosive charge or any other kind of payload is termed a kinetic projectile, kinetic energy weapon, kinetic energy warhead, kinetic warhead or kinetic penetrator. Typical kinetic energy weapons are blunt projectiles such as rocks and round shots, pointed ones such as arrows, somewhat pointed ones such as bullets.
Among projectiles that do not contain explosives are those launched from railguns and mass drivers, as well as kinetic energy penetrators. All of these weapons work by attaining a high muzzle velocity, or initial velocity up to, collide with their targets, converting their kinetic energy into destructive shock waves and heat. Other types of kinetic weapons are accelerated over time by gravity. In either case, it is the kinetic energy of the projectile; some kinetic weapons for targeting objects in spaceflight are anti-satellite weapons and anti-ballistic missiles. Since in order to reach an object in orbit it is necessary to attain an high velocity, their released kinetic energy alone is enough to destroy their target. For example: the energy of TNT is 4.6 MJ/kg, the energy of a kinetic kill vehicle with a closing speed of 10 km/s is of 50 MJ/kg. This saves costly weight and there is no detonation to be timed; this method, requires direct contact with the target, which requires a more accurate trajectory.
Some hit-to-kill warheads are additionally equipped with an explosive directional warhead to enhance the kill probability. With regard to anti-missile weapons, the Arrow missile and MIM-104 Patriot PAC-2 have explosives, while the Kinetic Energy Interceptor, Lightweight Exo-Atmospheric Projectile, THAAD do not. A kinetic projectile can be dropped from aircraft; this is applied by replacing the explosives of a regular bomb with a non-explosive material, for a precision hit with less collateral damage. A typical bomb has a speed of impact of 800 km/h, it is applied for training the act of dropping a bomb with explosives. This method has been used in Operation Iraqi Freedom and the subsequent military operations in Iraq by mating concrete-filled training bombs with JDAM GPS guidance kits, to attack vehicles and other "soft" targets located too close to civilian structures for the use of conventional high explosive bombs. A Prompt Global Strike may use a kinetic weapon. A kinetic bombardment may involve a projectile dropped from Earth orbit.
A hypothetical kinetic weapon that travels at a significant fraction of the speed of light found in science fiction, is termed a relativistic kill vehicle (RKV
Josiah Vavasseur was an English industrialist who founded Vavasseur and Co.. In 1883 the company merged with W. G. Armstrong and Company, Vavasseur became a director of the firm. Late in life he adopted Cecil Fisher, only son of admiral John Fisher, the Fisher family inherited his fortune, including Kilverstone Hall. Vavasseur was born in Braintree, Essex in 1834, following school he spent six years as an apprentice to the engineering firm of James Horn and Company in Whitechapel. In 1857 he partnered with David Guthrie in establishing the Patent Dyewood and Drug Mills, at 17 New Park Street, Southwark. By 1860, he was in business as Josiah Vavasseur and Company, engineers of 8 Sumner Street, Southwark, he obtained a patent for improvements in cannon rifling and the firm bought a small iron works at 28 Gravel Lane, Southwark. In the same year Vavasseur became a member of the Honourable Artillery Company. In 1861 he developed a portable machine for the rifling of smooth-bore guns, which he sold to Russia.
In 1862 Vavasseur's firm became subcontractor to captain Alexander Blakely, RA, who held a number of patents in gun construction and sold guns to countries in Europe, South America and North America, where demand was high due to the Civil War. Vavasseur produced a series of 2.9 inch guns for the Confederate States, but the ship carrying them foundered, they never reached their destination. Vavasseur's rifling machine was employed by Blakely for the rifling of some of his largest guns. In 1863 Vavasseur and Blakely collaborated on the production of spherical steel shot, intended to penetrate the armour of ironclads coming into service at the time. In 1863 Josiah Vavasseur and Company merged with The Blakely Cannon Company, resulting in the Blakely Ordnance Company, with Josiah Vavasseur as engineer and manager. In 1865 the new company became The Blakely Ordnance Company, Limited with Vavasseur as Resident Engineer. One year the panic of 1866 caused a squeeze on liquidity that forced The Blakely Ordnance Company, Limited into liquidation, Vavasseur out of his job.
The collapse of Blakely's enterprise made it possible for Vavasseur to buy back the iron works in Southwark, in 1867 the firm Josiah Vavasseur and Company was back in business referred to as the London Ordnance Works. The company took over at least one of the orders in the books of the Blakely Company, for 11-inch steel guns, delivered to Chile in 1867; the continuation of Blakely's projects was made easier by the fact that the strain on Blakely's personal finances had prevented the renewal of his gun patents. Vavasseur made smaller guns, including 27 12-pounders for France during the Franco-Prussian War 1870-1871; the production at the Ordnance Works included towed torpedoes of the Harvey design and spar torpedoes and mines designed by Captain Charles Ambrose McEvoy of the Confederate Navy. In 1866 he invented the copper rotating ring, or band, for the projectiles of breech-loading guns, this system was adopted; the patent laws of Prussia prevented Vavasseur from protecting his invention in that country, made it possible for the Krupp company to produce projectiles that Vavasseur saw as an infringement to his patent.
The inventor tried to protect his claims in 1877, when British shipyards were building the Fusō and the two Kongō class ironclads for Japan. They were all armed with Krupp guns, when the offending shells arrived in Britain, Vavasseur had an injunction placed on them. In the ensuing court case in 1878, it was decided that the Japanese Mikado could not be sued and that his property could not be held; the nature of the lawsuit was rather controversial and the verdict was cited in works on international law. In 1877 Vavasseur patented and developed a mounting for breech-loaded guns, which came to be used by most of the world's navies; the demand for the Vavasseur mounting was so high that London Ordnance Works was unable to cope, so in 1883 Josiah Vavasseur and Company merged with Sir W. G. Armstrong & Company; the Vavasseur company name disappeared, Josiah Vavasseur became a director, all production was transferred to the Elswick Works. Here "he continued his work of improving ordnance in every detail", until the last three or four years of his life, when ill-health prevented his attendance.
Josiah Vavasseur became a wealthy man, he was able to buy the manor of Kilverstone Hall and to donate substantial funds to religious and philanthropic undertakings. The major part of his fortune went to the only son of Admiral John Fisher; the story of the inheritance was retold by The New York Times on November 21, 1910, when Cecil Fisher came to the United States to marry miss Jane Morgan. The paper wrote that Cecil Fisher as a young lieutenant had helped Vavasseur with his work on quick-firing guns at Whale Island. A friendship evolved, Vavasseur had adopted Cecil on the condition that he would take the name and arms of Vavasseur; when Josiah Vavasseur died on November 13, 1908, Cecil Vavasseur Fisher inherited the equivalent of 2 million USD, when Admiral Fisher was made a baron on December 7, 1909, he took the name Baron Fisher of Kilverstone
Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the pressure relative to the ambient pressure. Various units are used to express pressure; some of these derive from a unit of force divided by a unit of area. Pressure may be expressed in terms of standard atmospheric pressure. Manometric units such as the centimetre of water, millimetre of mercury, inch of mercury are used to express pressures in terms of the height of column of a particular fluid in a manometer. Pressure is the amount of force applied at right angles to the surface of an object per unit area; the symbol for it is p or P. The IUPAC recommendation for pressure is a lower-case p. However, upper-case P is used; the usage of P vs p depends upon the field in which one is working, on the nearby presence of other symbols for quantities such as power and momentum, on writing style. Mathematically: p = F A, where: p is the pressure, F is the magnitude of the normal force, A is the area of the surface on contact.
Pressure is a scalar quantity. It relates the vector surface element with the normal force acting on it; the pressure is the scalar proportionality constant that relates the two normal vectors: d F n = − p d A = − p n d A. The minus sign comes from the fact that the force is considered towards the surface element, while the normal vector points outward; the equation has meaning in that, for any surface S in contact with the fluid, the total force exerted by the fluid on that surface is the surface integral over S of the right-hand side of the above equation. It is incorrect to say "the pressure is directed in such or such direction"; the pressure, as a scalar, has no direction. The force given by the previous relationship to the quantity has a direction, but the pressure does not. If we change the orientation of the surface element, the direction of the normal force changes accordingly, but the pressure remains the same. Pressure is distributed to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point.
It is a fundamental parameter in thermodynamics, it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre; this name for the unit was added in 1971. Other units of pressure, such as pounds per square inch and bar, are in common use; the CGS unit of pressure is 0.1 Pa.. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre and the like without properly identifying the force units, but using the names kilogram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2. Since a system under pressure has the potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume, it is therefore related to energy density and may be expressed in units such as joules per cubic metre. Mathematically: p =; some meteorologists prefer the hectopascal for atmospheric air pressure, equivalent to the older unit millibar. Similar pressures are given in kilopascals in most other fields, where the hecto- prefix is used.
The inch of mercury is still used in the United States. Oceanographers measure underwater pressure in decibars because pressure in the ocean increases by one decibar per metre depth; the standard atmosphere is an established constant. It is equal to typical air pressure at Earth mean sea level and is defined as 101325 Pa; because pressure is measured by its ability to displace a column of liquid in a manometer, pressures are expressed as a depth of a particular fluid. The most common choices are water; the pressure exerted by a column of liquid of height h and density ρ is given by the hydrostatic pressure equation p = ρgh, where g is the gravitational acceleration. Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column
Gunmetal known as red brass in the United States, is a type of bronze – an alloy of copper and zinc. Proportions vary by approximation but 88% copper, 8–10% tin, 2–4% zinc is an approximation. Used chiefly for making guns, it has been replaced by steel. Gunmetal, which casts and machines well and is resistant to corrosion from steam and salt water, is used to make steam and hydraulic castings, gears and various small objects, such as buttons, it has a tensile strength of 221 to 310 MPa, a specific gravity of 8.7, a Brinell hardness of 65 to 74, a melting point of around 1,000 degrees Celsius. Gunmetal ingot is a related alloy. Modified gunmetal contains lead in addition to the zinc, it is used for bearings. U. S. Government bronze specification G C90500 is composed of 88% copper, 10% tin, 2% zinc, as is British Admiralty gunmetal. G bronze contains 88% copper, 8% tin, 4% zinc. U. S. Government bronze specification H is composed of 83% copper, 14% tin, 3% zinc, 0.8% phosphorus. Red brass is used to produce pipes and plumbing fixtures and is considered to offer a good mixture of corrosion resistance and ease of casting.
It contains 85% copper, 5% tin, 5% lead, 5% zinc. Copper Alloy C23000, known as red brass, contains 84–86% copper, 0.05% each iron and lead, with the balance being zinc. Gunmetal can mean steel treated to simulate gunmetal bronze. Bushings made of this metal are used in machinery; the Victoria Cross, Britain's highest award for military valour, is traditionally made using gunmetal from a cannon captured at the Siege of Sevastopol during the Crimean War. Gun money, Irish late 17th-century emergency coins, contain gunmetal, as worn and scrapped guns were used to make them. Gunmetal as a colour is different from the reddish alloy of the same name described above, it is a shade of grey that has a bluish purplish tinge
The public domain consists of all the creative works to which no exclusive intellectual property rights apply. Those rights may have been forfeited, expressly waived, or may be inapplicable; the works of William Shakespeare and Beethoven, most early silent films, are in the public domain either by virtue of their having been created before copyright existed, or by their copyright term having expired. Some works are not covered by copyright, are therefore in the public domain—among them the formulae of Newtonian physics, cooking recipes, all computer software created prior to 1974. Other works are dedicated by their authors to the public domain; the term public domain is not applied to situations where the creator of a work retains residual rights, in which case use of the work is referred to as "under license" or "with permission". As rights vary by country and jurisdiction, a work may be subject to rights in one country and be in the public domain in another; some rights depend on registrations on a country-by-country basis, the absence of registration in a particular country, if required, gives rise to public-domain status for a work in that country.
The term public domain may be interchangeably used with other imprecise or undefined terms such as the "public sphere" or "commons", including concepts such as the "commons of the mind", the "intellectual commons", the "information commons". Although the term "domain" did not come into use until the mid-18th century, the concept "can be traced back to the ancient Roman Law, as a preset system included in the property right system." The Romans had a large proprietary rights system where they defined "many things that cannot be owned" as res nullius, res communes, res publicae and res universitatis. The term res nullius was defined as things not yet appropriated; the term res communes was defined as "things that could be enjoyed by mankind, such as air and ocean." The term res publicae referred to things that were shared by all citizens, the term res universitatis meant things that were owned by the municipalities of Rome. When looking at it from a historical perspective, one could say the construction of the idea of "public domain" sprouted from the concepts of res communes, res publicae, res universitatis in early Roman law.
When the first early copyright law was first established in Britain with the Statute of Anne in 1710, public domain did not appear. However, similar concepts were developed by French jurists in the 18th century. Instead of "public domain", they used terms such as publici juris or propriété publique to describe works that were not covered by copyright law; the phrase "fall in the public domain" can be traced to mid-19th century France to describe the end of copyright term. The French poet Alfred de Vigny equated the expiration of copyright with a work falling "into the sink hole of public domain" and if the public domain receives any attention from intellectual property lawyers it is still treated as little more than that, left when intellectual property rights, such as copyright and trademarks, expire or are abandoned. In this historical context Paul Torremans describes copyright as a, "little coral reef of private right jutting up from the ocean of the public domain." Copyright law differs by country, the American legal scholar Pamela Samuelson has described the public domain as being "different sizes at different times in different countries".
Definitions of the boundaries of the public domain in relation to copyright, or intellectual property more regard the public domain as a negative space. According to James Boyle this definition underlines common usage of the term public domain and equates the public domain to public property and works in copyright to private property. However, the usage of the term public domain can be more granular, including for example uses of works in copyright permitted by copyright exceptions; such a definition regards work in copyright as private property subject to fair-use rights and limitation on ownership. A conceptual definition comes from Lange, who focused on what the public domain should be: "it should be a place of sanctuary for individual creative expression, a sanctuary conferring affirmative protection against the forces of private appropriation that threatened such expression". Patterson and Lindberg described the public domain not as a "territory", but rather as a concept: "here are certain materials – the air we breathe, rain, life, thoughts, ideas, numbers – not subject to private ownership.
The materials that compose our cultural heritage must be free for all living to use no less than matter necessary for biological survival." The term public domain may be interchangeably used with other imprecise or undefined terms such as the "public sphere" or "commons", including concepts such as the "commons of the mind", the "intellectual commons", the "information commons". A public-domain book is a book with no copyright, a book, created without a license, or a book where its copyrights expired or have been forfeited. In most countries the term of protection of copyright lasts until January first, 70 years after the death of the latest living author; the longest copyright term is in Mexico, which has life plus 100 years for all deaths since July 1928. A notable exception is the United States, where every book and tale published prior to 1924 is in the public domain.