United States
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
Aircraft
An aircraft is a machine, able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. Common examples of aircraft include airplanes, airships and hot air balloons; the human activity that surrounds aircraft is called aviation. The science of aviation, including designing and building aircraft, is called aeronautics. Crewed aircraft are flown by an onboard pilot, but unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Aircraft may be classified by different criteria, such as lift type, aircraft propulsion and others. Flying model craft and stories of manned flight go back many centuries, however the first manned ascent – and safe descent – in modern times took place by larger hot-air balloons developed in the 18th century; each of the two World Wars led to great technical advances. The history of aircraft can be divided into five eras: Pioneers of flight, from the earliest experiments to 1914.
First World War, 1914 to 1918. Aviation between the World Wars, 1918 to 1939. Second World War, 1939 to 1945. Postwar era called the jet age, 1945 to the present day. Aerostats use buoyancy to float in the air in much the same way, they are characterized by one or more large gasbags or canopies, filled with a low-density gas such as helium, hydrogen, or hot air, less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces. Small hot-air balloons called sky lanterns were first invented in ancient China prior to the 3rd century BC and used in cultural celebrations, were only the second type of aircraft to fly, the first being kites which were first invented in ancient China over two thousand years ago. A balloon was any aerostat, while the term airship was used for large, powered aircraft designs – fixed-wing. In 1919 Frederick Handley Page was reported as referring to "ships of the air," with smaller passenger types as "Air yachts."
In the 1930s, large intercontinental flying boats were sometimes referred to as "ships of the air" or "flying-ships". – though none had yet been built. The advent of powered balloons, called dirigible balloons, of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft. Several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat and an "airship" is a powered one. A powered, steerable aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, sometimes dirigible balloon is regarded as the definition of an airship.
Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was adopted for tethered balloons; the nickname blimp was adopted along with the shape. In modern times, any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered. Heavier-than-air aircraft, such as airplanes, must find some way to push air or gas downwards, so that a reaction occurs to push the aircraft upwards; this dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust: aerodynamic lift, powered lift in the form of engine thrust. Aerodynamic lift involving wings is the most common, with fixed-wing aircraft being kept in the air by the forward movement of wings, rotorcraft by spinning wing-shaped rotors sometimes called rotary wings. A wing is a flat, horizontal surface shaped in cross-section as an aerofoil. To fly, air must generate lift.
A flexible wing is a wing made of fabric or thin sheet material stretched over a rigid frame. A kite is tethered to the ground and relies on the speed of the wind over its wings, which may be flexible or rigid, fixed, or rotary. With powered lift, the aircraft directs its engine thrust vertically downward. V/STOL aircraft, such as the Harrier Jump Jet and F-35B take off and land vertically using powered lift and transfer to aerodynamic lift in steady flight. A pure rocket is not regarded as an aerodyne, because it does not depend on the air for its lift. Rocket-powered missiles that obtain aerodynamic lift at high speed due to airflow over their bodies are a marginal case; the forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on the wind blowing over its wings to provide lift. Kites were the first kind of aircraft to fly, were invented in China around 500 BC.
Much aerodynamic research was done with kites before test aircraft, wind tunnels, computer modelling programs became available. The first heavier-than-air craft capable of controlled free-flight were gliders. A glider designed by Geo
Flying boat
A flying boat is a fixed-winged seaplane with a hull, allowing it to land on water, that has no type of landing gear to allow operation on land. It differs from a floatplane as it uses a purpose-designed fuselage which can float, granting the aircraft buoyancy. Flying boats may be stabilized by wing-like projections from the fuselage. Flying boats were some of the largest aircraft of the first half of the 20th century, exceeded in size only by bombers developed during World War II, their advantage lay in using water instead of expensive land-based runways, making them the basis for international airlines in the interwar period. They were commonly used for maritime patrol and air-sea rescue, their use trailed off after World War II because of the investments in airports during the war. In the 21st century, flying boats maintain a few niche uses, such as dropping water on forest fires, air transport around archipelagos, access to undeveloped areas. Many modern seaplane variants, whether float or flying boat types, are convertible amphibious aircraft where either landing gear or flotation modes may be used to land and take off.
The Frenchman Alphonse Pénaud filed the first patent for a flying machine with a boat hull and retractable landing gear in 1876, but Austrian Wilhelm Kress is credited with building the first seaplane Drachenflieger in 1898, although its two 30 hp Daimler engines were inadequate for take-off and it sank when one of its two floats collapsed. On 6 June 1905 Gabriel Voisin took off and landed on the River Seine with a towed kite glider on floats; the first of his unpowered flights was 150 yards. He built a powered floatplane in partnership with Louis Blériot, but the machine was unsuccessful. Other pioneers attempted to attach floats to aircraft in Britain, Australia and the USA. On 28 March 1910 Frenchman Henri Fabre flew the first successful powered seaplane, the Gnome Omega-powered hydravion, a trimaran floatplane. Fabre's first successful take off and landing by a powered seaplane inspired other aviators and he designed floats for several other flyers; the first hydro-aeroplane competition was held in Monaco in March 1912, featuring aircraft using floats from Fabre, Curtiss and Farman.
This led to the first scheduled seaplane passenger services at Aix-les-Bains, using a five-seat Sanchez-Besa from 1 August 1912. The French Navy ordered its first floatplane in 1912. In 1911–12 François Denhaut constructed the first seaplane with a fuselage forming a hull, using various designs to give hydrodynamic lift at take-off, its first successful flight was on 13 April 1912. Throughout 1910 and 1911 American pioneering aviator Glenn Curtiss developed his floatplane into the successful Curtiss Model D land-plane, which used a larger central float and sponsons. Combining floats with wheels, he made the first amphibian flights in February 1911 and was awarded the first Collier Trophy for US flight achievement. From 1912 his experiments with a hulled seaplane resulted in the 1913 Model E and Model F, which he called "flying-boats". In February 1911 the United States Navy took delivery of the Curtiss Model E, soon tested landings on and take-offs from ships using the Curtiss Model D. In Britain, Captain Edward Wakefield and Oscar Gnosspelius began to explore the feasibility of flight from water in 1908.
They decided to make use of Windermere in England's largest lake. The latter's first attempts to fly attracted large crowds, though the aircraft failed to take off and required a re-design of the floats incorporating features of Borwick’s successful speed-boat hulls. Meanwhile, Wakefield ordered a floatplane similar to the design of the 1910 Fabre Hydravion. By November 1911, both Gnosspelius and Wakefield had aircraft capable of flight from water and awaited suitable weather conditions. Gnosspelius's flight was short-lived. Wakefield’s pilot however, taking advantage of a light northerly wind took off and flew at a height of 50 feet to Ferry Nab, where he made a wide turn and returned for a perfect landing on the lake’s surface. In Switzerland, Emile Taddéoli equipped the Dufaux 4 biplane with swimmers and took off in 1912. A seaplane was used during the Balkan Wars in 1913, when a Greek "Astra Hydravion" did a reconnaissance of the Turkish fleet and dropped 4 bombs. In 1913, the Daily Mail newspaper put up a £10,000 prize for the first non-stop aerial crossing of the Atlantic, soon "enhanced by a further sum" from the Women's Aerial League of Great Britain.
American businessman Rodman Wanamaker became determined that the prize should go to an American aircraft and commissioned the Curtiss Aeroplane and Motor Company to design and build an aircraft capable of making the flight. Curtiss' development of the Flying Fish flying boat in 1913 brought him into contact with John Cyril Porte, a retired Royal Navy Lieutenant, aircraft designer and test pilot, to become an influential British aviation pioneer. Recognising that many of the early accidents were attributable to a poor understanding of handling while in contact with the water, the pair's efforts went into developing practical hull designs to make the transatlantic crossing possible. At the same time the British boat building firm J. Samuel White of Cowes on the Isle of Wight set up a new aircraft division and produced a flying boat in the United Kingdom; this was displayed at the London Air Show at Olympia in 1913. In that same year, a collaboration between the S. E. Saunders boatyard of East Cowes and the Sopwith Aviation Company produced the "Bat Boat", an aircraft with a consuta laminated hull that could operate from land or on water, which today we call an amphibious aircraft.
The "Bat Boat" completed s
Pfalz Flugzeugwerke
Pfalz Flugzeugwerke was a World War I German aircraft manufacturer, located at the Speyer airfield in the Palatinate. They are best known for their series of fighters, notably the Pfalz D. III and Pfalz D. XII; the company went bankrupt after the Armistice, when the French occupation forces confiscated all of the equipment, but the factory was re-used by various other companies until re-forming in 1997. Today they are a parts manufacturer referred to as PFW. Pfalz was the brainchild of son of a foundry owner in Neustadt an der Weinstraße, it appears that he had built his own aircraft between 1912 and 1913, although the exact origin of the design is unclear. On June 3, 1913, the Pfalz company was registered, consisting of Alfred, his brother Ernst, his brother-in-law Willy Sabersky-Müssigbrodt, as well as several investors: Richard and Eugen Kahn, August Kahn, they proposed to build designs from Albatros, but their attempts at a deal amounted to nothing. Their next deal was with Gustav Otto Flugzeugwerke, building examples of his pusher-propeller biplane design.
The original example was sent to Africa on a tour, ended up being pressed into service as a scout. The company had always planned to set up shop at the new airfield in Speyer, but they had problems securing land for a factory; the Gustav designs were built in the Speyer Festival Hall, unused at the time. It was not until February 6, 1914, that the city agreed to sell Pfalz 7,000 m² to build their factory. Construction was completed in July, only one month before the start of World War I. By this point, the company had arranged a license to produce Morane-Saulnier monoplanes, which were put into German service; when these became uncompetitive on the Western Front, Pfalz shifted production to the LFG Roland D. I and D. II; the D. II was produced into late 1916. Instead of licensing another design, Pfalz instead licensed the patented Roland firm's Wickelrumpf plywood strip-covered semi-monocoque fuselage design and combined it with the new 160 hp Mercedes D. III engine to create the Pfalz D. III; the D.
III entered service in August 1917, but was not considered a match for contemporary designs like the Albatros D. V, instead found a niche role in attacking observation balloons where its high diving speed was a major advantage. About 600 D. IIIs and modified D. IIIas were built between its replacement a year later. Many were still in service at that time, about 450. Adaptations of the D. III with the new Siemens-Halske Sh. III rotary resulted in the Pfalz D. VIII, which featured an incredible rate of climb; the Sh. III proved to be rather unreliable due to the ersatz engine oil available, only a small number of D. VIIIs were built; these did see front-line use by Jasta 2 at least, although it is unclear how many were built in total. The D. VIII was adapted to triplane configuration as the Pfalz Dr. I for entry in the First Fighter Competition at Adlershof in January 1918. Like the D. VIII, it was powered by the Sh. III, therefore outpowered its Oberursel UR. II powered contemporaries; the Fokker Dr. I was the winner of the contest, not surprising considering that it was the only aircraft entered, designed from the outset as a triplane, as opposed to being a quickly-adapted biplane.
About a dozen Dr. Is were built and used operationally for some time; the final major production model was the Pfalz D. XII, a development of the D. III that abandoned the sesquiplane configuration in favor of two-bay wings, similar in appearance to what looked like two-bay wings on the French SPAD fighters designed by Louis Béchereau, it entered the Second Fighter Competition in June 1918 against the famous Fokker E. V monoplane and other designs. Although similar to the Fokker D. VII in looks and performance, the D. XII was considered to be inferior in handling characteristics and difficult to land; the D. XII was ordered into production, about 800 were produced before the Armistice. Many of these were taken as booty by the Allies. A few aircraft were featured in various movies, notably Hell's Angels and The Dawn Patrol. A derivative of the D. XII, the D. XIV, was not ordered into the production. Pfalz's final scout, the D. XV, participated in the Third Fighter Competition; the Idflieg ordered the D. XV into production just before the Armistice, but it did not see operational service.
At the end of the war, the Pfalz factory fell into the French-occupied area, was stripped of anything useful. On June 4, 1919, the company was re-established as A. G. Pfalz, which listed its main businesses as "shipbuilding and the buying and selling of industrial goods." This company went bankrupt during the Great Depression in 1932. On October 1, 1937 the factories once again turned to aircraft work, this time under the name Saarpfalz Flugwerke, a maintenance company; the Speyer airfield was no longer operational, so aircraft repaired there had to be transported to Mannheim-Neuostheim for flight, but the city decided to rebuild the airport over the next year and it re-opened in 1938. The new company grew starting with over 200 employees by the end of 1937, growing to 500 by the start of the war, to 1,500 by the time the war ended, they maintained many designs during this time, including the Focke-Wulf Fw 58, Heinkel He 45, He 46, He 51 and He 111, Junkers Ju 52, Ju 88. Work at the plants ended in March 1945 due to the approach of French troops.
Ernst Heinkel introduced his famous bubblecar, the Heinkel K
Biplane
A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a biplane wing structure has a structural advantage over a monoplane, it produces more drag than a similar unbraced or cantilever monoplane wing. Improved structural techniques, better materials and the quest for greater speed made the biplane configuration obsolete for most purposes by the late 1930s. Biplanes offer several advantages over conventional cantilever monoplane designs: they permit lighter wing structures, low wing loading and smaller span for a given wing area. However, interference between the airflow over each wing increases drag and biplanes need extensive bracing, which causes additional drag. Biplanes are distinguished from tandem wing arrangements, where the wings are placed forward and aft, instead of above and below; the term is occasionally used in biology, to describe the wings of some flying animals.
In a biplane aircraft, two wings are placed one above the other. Each provides part of the lift, although they are not able to produce twice as much lift as a single wing of similar size and shape because the upper and the lower are working on nearly the same portion of the atmosphere and thus interfere with each other's behaviour. For example, in a wing of aspect ratio 6, a wing separation distance of one chord length, the biplane configuration will only produce about 20 percent more lift than a single wing of the same planform; the lower wing is attached to the fuselage, while the upper wing is raised above the fuselage with an arrangement of cabane struts, although other arrangements have been used. Either or both of the main wings can support ailerons, while flaps are more positioned on the lower wing. Bracing is nearly always added between the upper and lower wings, in the form of wires and/or slender interplane struts positioned symmetrically on either side of the fuselage; the primary advantage of the biplane over a monoplane is to combine great stiffness with light weight.
Stiffness requires structural depth and, where early monoplanes had to have this added with complicated extra bracing, the box kite or biplane has a deep structure and is therefore easier to make both light and strong. A braced monoplane wing must support itself while the two wings of a biplane help to stiffen each other; the biplane is therefore inherently stiffer than the monoplane. The structural forces in the spars of a biplane wing tend to be lower, so the wing can use less material to obtain the same overall strength and is therefore much lighter. A disadvantage of the biplane was the need for extra struts to space the wings apart, although the bracing required by early monoplanes reduced this disadvantage; the low power supplied by the engines available in the first years of aviation meant that aeroplanes could only fly slowly. This required an lower stalling speed, which in turn required a low wing loading, combining both large wing area with light weight. A biplane wing of a given span and chord has twice the area of a monoplane the same size and so can fly more or for a given flight speed can lift more weight.
Alternatively, a biplane wing of the same area as a monoplane has lower span and chord, reducing the structural forces and allowing it to be lighter. Biplanes suffer aerodynamic interference between the two planes; this means that a biplane does not in practice obtain twice the lift of the similarly-sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer. Given the low speed and power of early aircraft, the drag penalty of the wires and struts and the mutual interference of airflows were minor and acceptable factors; as engine power rose after World War One, the thick-winged cantilever monoplane became practicable and, with its inherently lower drag and higher speed, from around 1918 it began to replace the biplane in most fields of aviation. The smaller biplane wing allows greater maneuverability. During World War One, this further enhanced the dominance of the biplane and, despite the need for speed, military aircraft were among the last to abandon the biplane form.
Specialist sports aerobatic biplanes are still made. Biplanes were designed with the wings positioned directly one above the other. Moving the upper wing forward relative to the lower one is called positive stagger or, more simply stagger, it can help increase lift and reduce drag by reducing the aerodynamic interference effects between the two wings, makes access to the cockpit easier. Many biplanes have staggered wings. Common examples from the 1930s include the de Havilland Tiger Moth, Bücker Bü 131 Jungmann and Travel Air 2000, it is possible to place the lower wing's leading edge ahead of the upper wing, giving negative stagger. This is done in a given design for practical engineering reasons. Examples of negative stagger include Breguet 14 and Beechcraft Staggerwing. However, positive stagger is more common; the space enclosed by a set of interplane struts is called a bay, hence a biplane or triplane with one set of such struts connecting the wings on each side of the aircraft is a single-bay biplane.
This provided sufficient strength for smaller aircraft such as the First World War-era Fokker D. VII fighter and the Second World War de Havilland Tiger Moth basic trainer; the larger two-seat Curtiss JN-4 Jenny is a two bay biplane, the extra bay being necessary as overlong bays are prone to flexing and can fail. The SPAD S. XIII fighter, while appearing to be a two bay bip
Materials science
The interdisciplinary field of materials science commonly termed materials science and engineering is the design and discovery of new materials solids. The intellectual origins of materials science stem from the Enlightenment, when researchers began to use analytical thinking from chemistry and engineering to understand ancient, phenomenological observations in metallurgy and mineralogy. Materials science still incorporates elements of physics and engineering; as such, the field was long considered by academic institutions as a sub-field of these related fields. Beginning in the 1940s, materials science began to be more recognized as a specific and distinct field of science and engineering, major technical universities around the world created dedicated schools of the study, within either the Science or Engineering schools, hence the naming. Materials science is a syncretic discipline hybridizing metallurgy, solid-state physics, chemistry, it is the first example of a new academic discipline emerging by fusion rather than fission.
Many of the most pressing scientific problems humans face are due to the limits of the materials that are available and how they are used. Thus, breakthroughs in materials science are to affect the future of technology significantly. Materials scientists emphasize understanding how the history of a material influences its structure, thus the material's properties and performance; the understanding of processing-structure-properties relationships is called the § materials paradigm. This paradigm is used to advance understanding in a variety of research areas, including nanotechnology and metallurgy. Materials science is an important part of forensic engineering and failure analysis – investigating materials, structures or components which fail or do not function as intended, causing personal injury or damage to property; such investigations are key to understanding, for example, the causes of various aviation accidents and incidents. The material of choice of a given era is a defining point. Phrases such as Stone Age, Bronze Age, Iron Age, Steel Age are historic, if arbitrary examples.
Deriving from the manufacture of ceramics and its putative derivative metallurgy, materials science is one of the oldest forms of engineering and applied science. Modern materials science evolved directly from metallurgy, which itself evolved from mining and ceramics and earlier from the use of fire. A major breakthrough in the understanding of materials occurred in the late 19th century, when the American scientist Josiah Willard Gibbs demonstrated that the thermodynamic properties related to atomic structure in various phases are related to the physical properties of a material. Important elements of modern materials science are a product of the space race: the understanding and engineering of the metallic alloys, silica and carbon materials, used in building space vehicles enabling the exploration of space. Materials science has driven, been driven by, the development of revolutionary technologies such as rubbers, plastics and biomaterials. Before the 1960s, many eventual materials science departments were metallurgy or ceramics engineering departments, reflecting the 19th and early 20th century emphasis on metals and ceramics.
The growth of materials science in the United States was catalyzed in part by the Advanced Research Projects Agency, which funded a series of university-hosted laboratories in the early 1960s "to expand the national program of basic research and training in the materials sciences." The field has since broadened to include every class of materials, including ceramics, semiconductors, magnetic materials and nanomaterials classified into three distinct groups: ceramics and polymers. The prominent change in materials science during the recent decades is active usage of computer simulations to find new materials, predict properties, understand phenomena. A material is defined as a substance, intended to be used for certain applications. There are a myriad of materials around us—they can be found in anything from buildings to spacecraft. Materials can be further divided into two classes: crystalline and non-crystalline; the traditional examples of materials are metals, semiconductors and polymers.
New and advanced materials that are being developed include nanomaterials and energy materials to name a few. The basis of materials science involves studying the structure of materials, relating them to their properties. Once a materials scientist knows about this structure-property correlation, they can go on to study the relative performance of a material in a given application; the major determinants of the structure of a material and thus of its properties are its constituent chemical elements and the way in which it has been processed into its final form. These characteristics, taken together and related through the laws of thermodynamics and kinetics, govern a material's microstructure, thus its properties; as mentioned above, structure is one of the most important components of the field of materials science. Materials science examines the structure of materials from the atomic scale, all the way up to the macro scale. Characterization is the way; this involves methods such as diffraction with X-rays, electrons, or neutrons, various forms of spectroscopy and chemical analysis such as Raman spectroscopy, energy-dispersive spectroscopy, thermal analysis, electron microscope analysis, etc.
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Propulsion
Propulsion means to push forward or drive an object forward. The term is derived from two Latin words: pro, meaning forward. A propulsion system consists of a source of mechanical power, a propulsor. A technological system uses an engine or motor as the power source, wheels and axles, propellers, or a propulsive nozzle to generate the force. Components such as clutches or gearboxes may be needed to connect the motor to axles, wheels, or propellers. Biological propulsion systems use an animal's muscles as the power source, limbs such as wings, fins or legs as the propulsors. A technological/biological system may use human, or trained animal, muscular work to power a mechanical device. An aircraft propulsion system consists of an aircraft engine and some means to generate thrust, such as a propeller or a propulsive nozzle. An aircraft propulsion system must achieve two things. First, the thrust from the propulsion system must balance the drag of the airplane when the airplane is cruising, and second, the thrust from the propulsion system must exceed the drag of the airplane for the airplane to accelerate.
The greater the difference between the thrust and the drag, called the excess thrust, the faster the airplane will accelerate. Some aircraft, like airliners and cargo planes, spend most of their life in a cruise condition. For these airplanes, excess thrust is not as important as low fuel usage. Since thrust depends on both the amount of gas moved and the velocity, we can generate high thrust by accelerating a large mass of gas by a small amount, or by accelerating a small mass of gas by a large amount; because of the aerodynamic efficiency of propellers and fans, it is more fuel efficient to accelerate a large mass by a small amount, why high-bypass turbofans and turboprops are used on cargo planes and airliners. Some aircraft, like fighter planes or experimental high speed aircraft, require high excess thrust to accelerate and to overcome the high drag associated with high speeds. For these airplanes, engine efficiency is not as important as high thrust. Modern combat aircraft have an afterburner added to a low bypass turbofan.
Future hypersonic aircraft may use some type of rocket propulsion. Ground propulsion is any mechanism for propelling solid bodies along the ground for the purposes of transportation; the propulsion system consists of a combination of an engine or motor, a gearbox and wheel and axles in standard applications. Maglev is a system of transportation that uses magnetic levitation to suspend and propel vehicles with magnets rather than using mechanical methods, such as wheels and bearings. With maglev a vehicle is levitated a short distance away from a guide way using magnets to create both lift and thrust. Maglev vehicles are claimed to move more smoothly and and to require less maintenance than wheeled mass transit systems, it is claimed that non-reliance on friction means that acceleration and deceleration can far surpass that of existing forms of transport. The power needed for levitation is not a large percentage of the overall energy consumption. Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water.
While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting a motor or engine turning a propeller, or less in jet drives, an impeller. Marine engineering is the discipline concerned with the design of marine propulsion systems. Steam engines were the first mechanical engines used in marine propulsion, but have been replaced by two-stroke or four-stroke diesel engines, outboard motors, gas turbine engines on faster ships. Nuclear reactors producing steam are used to propel warships and icebreakers, there have been attempts to utilize them to power commercial vessels. Electric motors have been used on submarines and electric boats and have been proposed for energy-efficient propulsion. Recent development in liquified natural gas fueled engines are gaining recognition for their low emissions and cost advantages. Spacecraft propulsion is any method used to accelerate artificial satellites. There are many different methods; each method has drawbacks and advantages, spacecraft propulsion is an active area of research.
However, most spacecraft today are propelled by forcing a gas from the back/rear of the vehicle at high speed through a supersonic de Laval nozzle. This sort of engine is called a rocket engine. All current spacecraft use chemical rockets for launch, though some have used air-breathing engines on their first stage. Most satellites have simple reliable chemical thrusters or resistojet rockets for orbital station-keeping and some use momentum wheels for attitude control. Soviet bloc satellites have used electric propulsion for decades, newer Western geo-orbiting spacecraft are starting to use them for north-south stationkeeping and orbit raising. Interplanetary vehicles use chemical rockets as well, although a few have used ion thrusters and Hall effect thrusters to great success. A cable car is any of a variety of transportation systems relying on cables to pull vehicles along or lower them at a steady rate; the terminology refers to the vehicles on these systems. The cable car vehicles are motor
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