Georges Creek Valley is located in Allegany County, Maryland along the Georges Creek . The valley is rich in wide veins of coal , known historically as " The Big Vein ." Coal was once extracted by deep mines but is only mined today through surface mining . The Georges Creek Valley was once a major center for the US coal industry.
127-608: A series of small mining towns were founded along the Georges Creek Valley in the nineteenth century when coal was discovered in the region. This led mining companies in the valley to develop railroads for transporting the coal. Some of these railroads were merged into the Cumberland and Pennsylvania Railroad System between 1853 and 1870. A competing railroad, the George's Creek and Cumberland Railroad , operated in
254-408: A crank on a driving axle. Steam locomotives have been phased out in most parts of the world for economical and safety reasons, although many are preserved in working order by heritage railways . Electric locomotives draw power from a stationary source via an overhead wire or third rail . Some also or instead use a battery . In locomotives that are powered by high-voltage alternating current ,
381-586: A dining car . Some lines also provide over-night services with sleeping cars . Some long-haul trains have been given a specific name . Regional trains are medium distance trains that connect cities with outlying, surrounding areas, or provide a regional service, making more stops and having lower speeds. Commuter trains serve suburbs of urban areas, providing a daily commuting service. Airport rail links provide quick access from city centres to airports . High-speed rail are special inter-city trains that operate at much higher speeds than conventional railways,
508-731: A fourth rail system in 1890 on the City and South London Railway , now part of the London Underground Northern line . This was the first major railway to use electric traction . The world's first deep-level electric railway, it runs from the City of London , under the River Thames , to Stockwell in south London. The first practical AC electric locomotive was designed by Charles Brown , then working for Oerlikon , Zürich. In 1891, Brown had demonstrated long-distance power transmission, using three-phase AC , between
635-542: A funicular railway at the Hohensalzburg Fortress in Austria. The line originally used wooden rails and a hemp haulage rope and was operated by human or animal power, through a treadwheel . The line is still operational, although in updated form and is possibly the oldest operational railway. Wagonways (or tramways ) using wooden rails, hauled by horses, started appearing in the 1550s to facilitate
762-492: A hydro-electric plant at Lauffen am Neckar and Frankfurt am Main West, a distance of 280 km (170 mi). Using experience he had gained while working for Jean Heilmann on steam–electric locomotive designs, Brown observed that three-phase motors had a higher power-to-weight ratio than DC motors and, because of the absence of a commutator , were simpler to manufacture and maintain. However, they were much larger than
889-431: A steam engine that provides adhesion. Coal , petroleum , or wood is burned in a firebox , boiling water in the boiler to create pressurized steam. The steam travels through the smokebox before leaving via the chimney or smoke stack. In the process, it powers a piston that transmits power directly through a connecting rod (US: main rod) and a crankpin (US: wristpin) on the driving wheel (US main driver) or to
1016-469: A transformer in the locomotive converts the high-voltage low-current power to low-voltage high current used in the traction motors that power the wheels. Modern locomotives may use three-phase AC induction motors or direct current motors. Under certain conditions, electric locomotives are the most powerful traction. They are also the cheapest to run and provide less noise and no local air pollution. However, they require high capital investments both for
1143-550: A diesel locomotive from the company in 1909. The world's first diesel-powered locomotive was operated in the summer of 1912 on the Winterthur–Romanshorn railway in Switzerland, but was not a commercial success. The locomotive weight was 95 tonnes and the power was 883 kW with a maximum speed of 100 km/h (62 mph). Small numbers of prototype diesel locomotives were produced in a number of countries through
1270-478: A double track plateway, erroneously sometimes cited as world's first public railway, in south London. William Jessop had earlier used a form of all-iron edge rail and flanged wheels successfully for an extension to the Charnwood Forest Canal at Nanpantan , Loughborough, Leicestershire in 1789. In 1790, Jessop and his partner Outram began to manufacture edge rails. Jessop became a partner in
1397-645: A graphene sheet in the presence of graphene-adsorbed oxygen. Despite being a simplified model of friction, the Coulomb model is useful in many numerical simulation applications such as multibody systems and granular material . Even its most simple expression encapsulates the fundamental effects of sticking and sliding which are required in many applied cases, although specific algorithms have to be designed in order to efficiently numerically integrate mechanical systems with Coulomb friction and bilateral or unilateral contact. Some quite nonlinear effects , such as
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#17327802026471524-437: A large turning radius in its design. While high-speed rail is most often designed for passenger travel, some high-speed systems also offer freight service. Since 1980, rail transport has changed dramatically, but a number of heritage railways continue to operate as part of living history to preserve and maintain old railway lines for services of tourist trains. A train is a connected series of rail vehicles that move along
1651-498: A larger locomotive named Galvani , exhibited at the Royal Scottish Society of Arts Exhibition in 1841. The seven-ton vehicle had two direct-drive reluctance motors , with fixed electromagnets acting on iron bars attached to a wooden cylinder on each axle, and simple commutators . It hauled a load of six tons at four miles per hour (6 kilometers per hour) for a distance of one and a half miles (2.4 kilometres). It
1778-423: A locomotive. This involves one or more powered vehicles being located at the front of the train, providing sufficient tractive force to haul the weight of the full train. This arrangement remains dominant for freight trains and is often used for passenger trains. A push–pull train has the end passenger car equipped with a driver's cab so that the engine driver can remotely control the locomotive. This allows one of
1905-411: A new surface forms at the back of a sliding true contact, and existing surface disappears at the front of it. Since all surfaces involve the thermodynamic surface energy, work must be spent in creating the new surface, and energy is released as heat in removing the surface. Thus, a force is required to move the back of the contact, and frictional heat is released at the front. For certain applications, it
2032-477: A number of trains per hour (tph). Passenger trains can usually be into two types of operation, intercity railway and intracity transit. Whereas intercity railway involve higher speeds, longer routes, and lower frequency (usually scheduled), intracity transit involves lower speeds, shorter routes, and higher frequency (especially during peak hours). Intercity trains are long-haul trains that operate with few stops between cities. Trains typically have amenities such as
2159-400: A parameter describing the scaling behavior of surface asperities, is known to play an important role in determining the magnitude of the static friction. For surfaces in relative motion μ = μ k {\displaystyle \mu =\mu _{\mathrm {k} }} , where μ k {\displaystyle \mu _{\mathrm {k} }} is
2286-676: A piece of circular rail track in Bloomsbury , London, the Catch Me Who Can , but never got beyond the experimental stage with railway locomotives, not least because his engines were too heavy for the cast-iron plateway track then in use. The first commercially successful steam locomotive was Matthew Murray 's rack locomotive Salamanca built for the Middleton Railway in Leeds in 1812. This twin-cylinder locomotive
2413-465: A pivotal role in the development and widespread adoption of the steam locomotive. His designs considerably improved on the work of the earlier pioneers. He built the locomotive Blücher , also a successful flanged -wheel adhesion locomotive. In 1825 he built the locomotive Locomotion for the Stockton and Darlington Railway in the northeast of England, which became the first public steam railway in
2540-439: A revival in recent decades due to road congestion and rising fuel prices, as well as governments investing in rail as a means of reducing CO 2 emissions . Smooth, durable road surfaces have been made for wheeled vehicles since prehistoric times. In some cases, they were narrow and in pairs to support only the wheels. That is, they were wagonways or tracks. Some had grooves or flanges or other mechanical means to keep
2667-472: A rough body driven over a rough surface, the mechanical work done by the driver exceeds the mechanical work received by the surface. The lost work is accounted for by heat generated by friction. Over the years, for example in his 1879 thesis, but particularly in 1926, Planck advocated regarding the generation of heat by rubbing as the most specific way to define heat, and the prime example of an irreversible thermodynamic process. The focus of research during
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#17327802026472794-739: A single lever to control both engine and generator in a coordinated fashion, and was the prototype for all diesel–electric locomotive control systems. In 1914, world's first functional diesel–electric railcars were produced for the Königlich-Sächsische Staatseisenbahnen ( Royal Saxon State Railways ) by Waggonfabrik Rastatt with electric equipment from Brown, Boveri & Cie and diesel engines from Swiss Sulzer AG . They were classified as DET 1 and DET 2 ( de.wiki ). The first regular used diesel–electric locomotives were switcher (shunter) locomotives . General Electric produced several small switching locomotives in
2921-515: A single study has demonstrated the potential for an effectively negative coefficient of friction in the low-load regime , meaning that a decrease in normal force leads to an increase in friction. This contradicts everyday experience in which an increase in normal force leads to an increase in friction. This was reported in the journal Nature in October 2012 and involved the friction encountered by an atomic force microscope stylus when dragged across
3048-407: A standard. Following SNCF's successful trials, 50 Hz, now also called industrial frequency was adopted as standard for main-lines across the world. Earliest recorded examples of an internal combustion engine for railway use included a prototype designed by William Dent Priestman . Sir William Thomson examined it in 1888 and described it as a "Priestman oil engine mounted upon a truck which
3175-632: A terminus about one-half mile (800 m) away. A funicular railway was also made at Broseley in Shropshire some time before 1604. This carried coal for James Clifford from his mines down to the River Severn to be loaded onto barges and carried to riverside towns. The Wollaton Wagonway , completed in 1604 by Huntingdon Beaumont , has sometimes erroneously been cited as the earliest British railway. It ran from Strelley to Wollaton near Nottingham . The Middleton Railway in Leeds , which
3302-419: A threshold value for this force, above which motion would commence. This maximum force is known as traction . The force of friction is always exerted in a direction that opposes movement (for kinetic friction) or potential movement (for static friction) between the two surfaces. For example, a curling stone sliding along the ice experiences a kinetic force slowing it down. For an example of potential movement,
3429-434: A very poor approximation (for example, adhesive tape resists sliding even when there is no normal force, or a negative normal force). In this case, the frictional force may depend strongly on the area of contact. Some drag racing tires are adhesive for this reason. However, despite the complexity of the fundamental physics behind friction, the relationships are accurate enough to be useful in many applications. As of 2012 ,
3556-408: A wheel. This was a large stationary engine , powering cotton mills and a variety of machinery; the state of boiler technology necessitated the use of low-pressure steam acting upon a vacuum in the cylinder, which required a separate condenser and an air pump . Nevertheless, as the construction of boilers improved, Watt investigated the use of high-pressure steam acting directly upon a piston, raising
3683-409: Is (highly ordered pyrolytic) graphite which can have a friction coefficient below 0.01. This ultralow-friction regime is called superlubricity . Static friction is friction between two or more solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a sloped surface. The coefficient of static friction, typically denoted as μ s ,
3810-498: Is a dimensionless scalar value which equals the ratio of the force of friction between two bodies and the force pressing them together, either during or at the onset of slipping. The coefficient of friction depends on the materials used; for example, ice on steel has a low coefficient of friction, while rubber on pavement has a high coefficient of friction. Coefficients of friction range from near zero to greater than one. The coefficient of friction between two surfaces of similar metals
3937-531: Is a means of transport using wheeled vehicles running in tracks , which usually consist of two parallel steel rails . Rail transport is one of the two primary means of land transport , next to road transport . It is used for about 8% of passenger and freight transport globally, thanks to its energy efficiency and potentially high speed . Rolling stock on rails generally encounters lower frictional resistance than rubber-tyred road vehicles, allowing rail cars to be coupled into longer trains . Power
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4064-410: Is a single, self-powered car, and may be electrically propelled or powered by a diesel engine . Multiple units have a driver's cab at each end of the unit, and were developed following the ability to build electric motors and other engines small enough to fit under the coach. There are only a few freight multiple units, most of which are high-speed post trains. Steam locomotives are locomotives with
4191-408: Is an empirical measurement — it has to be measured experimentally , and cannot be found through calculations. Rougher surfaces tend to have higher effective values. Both static and kinetic coefficients of friction depend on the pair of surfaces in contact; for a given pair of surfaces, the coefficient of static friction is usually larger than that of kinetic friction; in some sets
4318-495: Is an approximate model used to calculate the force of dry friction. It is governed by the model: F f ≤ μ F n , {\displaystyle F_{\mathrm {f} }\leq \mu F_{\mathrm {n} },} where The Coulomb friction F f {\displaystyle F_{\mathrm {f} }} may take any value from zero up to μ F n {\displaystyle \mu F_{\mathrm {n} }} , and
4445-399: Is dominant. Electro-diesel locomotives are built to run as diesel–electric on unelectrified sections and as electric locomotives on electrified sections. Alternative methods of motive power include magnetic levitation , horse-drawn, cable , gravity, pneumatics and gas turbine . A passenger train stops at stations where passengers may embark and disembark. The oversight of the train is
4572-437: Is greater than that between two surfaces of different metals; for example, brass has a higher coefficient of friction when moved against brass, but less if moved against steel or aluminum. For surfaces at rest relative to each other, μ = μ s {\displaystyle \mu =\mu _{\mathrm {s} }} , where μ s {\displaystyle \mu _{\mathrm {s} }}
4699-424: Is impending, is sometimes referred to as limiting friction , although this term is not used universally. Kinetic friction , also known as dynamic friction or sliding friction , occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μ k , and is usually less than the coefficient of static friction for
4826-415: Is maintained that μ is always < 1, but this is not true. While in most relevant applications μ < 1, a value above 1 merely implies that the force required to slide an object along the surface is greater than the normal force of the surface on the object. For example, silicone rubber or acrylic rubber -coated surfaces have a coefficient of friction that can be substantially larger than 1. While it
4953-562: Is more useful to define static friction in terms of the maximum angle before which one of the items will begin sliding. This is called the angle of friction or friction angle . It is defined as: tan θ = μ s {\displaystyle \tan {\theta }=\mu _{\mathrm {s} }} and thus: θ = arctan μ s {\displaystyle \theta =\arctan {\mu _{\mathrm {s} }}} where θ {\displaystyle \theta }
5080-479: Is no sliding occurring, the friction force can have any value from zero up to F max {\displaystyle F_{\text{max}}} . Any force smaller than F max {\displaystyle F_{\text{max}}} attempting to slide one surface over the other is opposed by a frictional force of equal magnitude and opposite direction. Any force larger than F max {\displaystyle F_{\text{max}}} overcomes
5207-456: Is often stated that the COF is a "material property," it is better categorized as a "system property." Unlike true material properties (such as conductivity, dielectric constant, yield strength), the COF for any two materials depends on system variables like temperature , velocity , atmosphere and also what are now popularly described as aging and deaging times; as well as on geometric properties of
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5334-434: Is on a level surface and subjected to an external force P {\displaystyle P} tending to cause it to slide, then the normal force between the object and the surface is just N = m g + P y {\displaystyle N=mg+P_{y}} , where m g {\displaystyle mg} is the block's weight and P y {\displaystyle P_{y}}
5461-423: Is perpendicular to the surfaces. In the simple case of a mass resting on a horizontal surface, the only component of the normal force is the force due to gravity, where N = m g {\displaystyle N=mg\,} . In this case, conditions of equilibrium tell us that the magnitude of the friction force is zero , F f = 0 {\displaystyle F_{f}=0} . In fact,
5588-409: Is proportional to the normal force (until saturation, which takes place when all area is in atomic contact); and that the frictional force is proportional to the applied normal force, independently of the contact area. The Coulomb approximation is fundamentally an empirical construct. It is a rule-of-thumb describing the approximate outcome of an extremely complicated physical interaction. The strength of
5715-573: Is responsible for the Coulomb damping of an oscillating or vibrating system. New models are beginning to show how kinetic friction can be greater than static friction. In many other cases roughness effects are dominant, for example in rubber to road friction. Surface roughness and contact area affect kinetic friction for micro- and nano-scale objects where surface area forces dominate inertial forces. The origin of kinetic friction at nanoscale can be rationalized by an energy model. During sliding,
5842-466: Is the coefficient of static friction . This is usually larger than its kinetic counterpart. The coefficient of static friction exhibited by a pair of contacting surfaces depends upon the combined effects of material deformation characteristics and surface roughness , both of which have their origins in the chemical bonding between atoms in each of the bulk materials and between the material surfaces and any adsorbed material . The fractality of surfaces,
5969-412: Is the angle from horizontal and μ s is the static coefficient of friction between the objects. This formula can also be used to calculate μ s from empirical measurements of the friction angle. Determining the forces required to move atoms past each other is a challenge in designing nanomachines . In 2008 scientists for the first time were able to move a single atom across a surface, and measure
6096-497: Is the downward component of the external force. Prior to sliding, this friction force is F f = − P x {\displaystyle F_{f}=-P_{x}} , where P x {\displaystyle P_{x}} is the horizontal component of the external force. Thus, F f ≤ μ N {\displaystyle F_{f}\leq \mu N} in general. Sliding commences only after this frictional force reaches
6223-471: Is transformed to heat as well as the free energy of the structural changes and other types of dissipation , so mechanical energy is not conserved. The complexity of the interactions involved makes the calculation of friction from first principles difficult and it is often easier to use empirical methods for analysis and the development of theory. There are several types of friction: Many ancient authors including Aristotle , Vitruvius , and Pliny
6350-537: Is usually higher than the coefficient of kinetic friction. Static friction is considered to arise as the result of surface roughness features across multiple length scales at solid surfaces. These features, known as asperities are present down to nano-scale dimensions and result in true solid to solid contact existing only at a limited number of points accounting for only a fraction of the apparent or nominal contact area. The linearity between applied load and true contact area, arising from asperity deformation, gives rise to
6477-408: Is usually provided by diesel or electrical locomotives . While railway transport is capital-intensive and less flexible than road transport, it can carry heavy loads of passengers and cargo with greater energy efficiency and safety. Precursors of railways driven by human or animal power have existed since antiquity, but modern rail transport began with the invention of the steam locomotive in
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#17327802026476604-556: Is worked on a temporary line of rails to show the adaptation of a petroleum engine for locomotive purposes." In 1894, a 20 hp (15 kW) two axle machine built by Priestman Brothers was used on the Hull Docks . In 1906, Rudolf Diesel , Adolf Klose and the steam and diesel engine manufacturer Gebrüder Sulzer founded Diesel-Sulzer-Klose GmbH to manufacture diesel-powered locomotives. Sulzer had been manufacturing diesel engines since 1898. The Prussian State Railways ordered
6731-692: The United Kingdom at the beginning of the 19th century. The first passenger railway, the Stockton and Darlington Railway , opened in 1825. The quick spread of railways throughout Europe and North America, following the 1830 opening of the first intercity connection in England, was a key component of the Industrial Revolution . The adoption of rail transport lowered shipping costs compared to water transport, leading to "national markets" in which prices varied less from city to city. In
6858-615: The United Kingdom , South Korea , Scandinavia, Belgium and the Netherlands. The construction of many of these lines has resulted in the dramatic decline of short-haul flights and automotive traffic between connected cities, such as the London–Paris–Brussels corridor, Madrid–Barcelona, Milan–Rome–Naples, as well as many other major lines. High-speed trains normally operate on standard gauge tracks of continuously welded rail on grade-separated right-of-way that incorporates
6985-860: The atomic scale , showing that, on that scale, dry friction is the product of the inter-surface shear stress and the contact area. These two discoveries explain Amonton's first law (below) ; the macroscopic proportionality between normal force and static frictional force between dry surfaces. The elementary property of sliding (kinetic) friction were discovered by experiment in the 15th to 18th centuries and were expressed as three empirical laws: Dry friction resists relative lateral motion of two solid surfaces in contact. The two regimes of dry friction are 'static friction' (" stiction ") between non-moving surfaces, and kinetic friction (sometimes called sliding friction or dynamic friction) between moving surfaces. Coulomb friction, named after Charles-Augustin de Coulomb ,
7112-400: The coefficient of kinetic friction . The Coulomb friction is equal to F f {\displaystyle F_{\mathrm {f} }} , and the frictional force on each surface is exerted in the direction opposite to its motion relative to the other surface. Arthur Morin introduced the term and demonstrated the utility of the coefficient of friction. The coefficient of friction
7239-414: The overhead lines and the supporting infrastructure, as well as the generating station that is needed to produce electricity. Accordingly, electric traction is used on urban systems, lines with high traffic and for high-speed rail. Diesel locomotives use a diesel engine as the prime mover . The energy transmission may be either diesel–electric , diesel-mechanical or diesel–hydraulic but diesel–electric
7366-458: The puddling process in 1784. In 1783 Cort also patented the rolling process , which was 15 times faster at consolidating and shaping iron than hammering. These processes greatly lowered the cost of producing iron and rails. The next important development in iron production was hot blast developed by James Beaumont Neilson (patented 1828), which considerably reduced the amount of coke (fuel) or charcoal needed to produce pig iron. Wrought iron
7493-418: The rotary phase converter , enabling electric locomotives to use three-phase motors whilst supplied via a single overhead wire, carrying the simple industrial frequency (50 Hz) single phase AC of the high-voltage national networks. An important contribution to the wider adoption of AC traction came from SNCF of France after World War II. The company conducted trials at AC 50 Hz, and established it as
7620-462: The vertical shaft mines of Pennsylvania and West Virginia . Still, the regional miners, blackened from head to foot when they emerged from a mine at the end of a day, knew that the carbon -filled air, which corroded the lungs over time, would lead to an early death. After World War I , coal production started to decline, and today only some strip mining remains as the last vestige of this once all-important industry. Coal trains once went through
7747-404: The 'song' of a glass harp , phenomena which involve stick and slip, modelled as a drop of friction coefficient with velocity. A practically important case is the self-oscillation of the strings of bowed instruments such as the violin , cello , hurdy-gurdy , erhu , etc. A connection between dry friction and flutter instability in a simple mechanical system has been discovered, watch
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#17327802026477874-540: The 1880s, railway electrification began with tramways and rapid transit systems. Starting in the 1940s, steam locomotives were replaced by diesel locomotives . The first high-speed railway system was introduced in Japan in 1964, and high-speed rail lines now connect many cities in Europe , East Asia , and the eastern United States . Following some decline due to competition from cars and airplanes, rail transport has had
8001-521: The 1930s (the famous " 44-tonner " switcher was introduced in 1940) Westinghouse Electric and Baldwin collaborated to build switching locomotives starting in 1929. In 1929, the Canadian National Railways became the first North American railway to use diesels in mainline service with two units, 9000 and 9001, from Westinghouse. Although steam and diesel services reaching speeds up to 200 km/h (120 mph) were started before
8128-508: The 1960s in Europe, they were not very successful. The first electrified high-speed rail Tōkaidō Shinkansen was introduced in 1964 between Tokyo and Osaka in Japan. Since then high-speed rail transport, functioning at speeds up to and above 300 km/h (190 mph), has been built in Japan, Spain, France , Germany, Italy, the People's Republic of China, Taiwan (Republic of China),
8255-435: The 20th century has been to understand the physical mechanisms behind friction. Frank Philip Bowden and David Tabor (1950) showed that, at a microscopic level , the actual area of contact between surfaces is a very small fraction of the apparent area. This actual area of contact, caused by asperities increases with pressure. The development of the atomic force microscope (ca. 1986) enabled scientists to study friction at
8382-464: The 40 km Burgdorf–Thun line , Switzerland. Italian railways were the first in the world to introduce electric traction for the entire length of a main line rather than a short section. The 106 km Valtellina line was opened on 4 September 1902, designed by Kandó and a team from the Ganz works. The electrical system was three-phase at 3 kV 15 Hz. In 1918, Kandó invented and developed
8509-530: The Butterley Company in 1790. The first public edgeway (thus also first public railway) built was Lake Lock Rail Road in 1796. Although the primary purpose of the line was to carry coal, it also carried passengers. These two systems of constructing iron railways, the "L" plate-rail and the smooth edge-rail, continued to exist side by side until well into the early 19th century. The flanged wheel and edge-rail eventually proved its superiority and became
8636-514: The DC motors of the time and could not be mounted in underfloor bogies : they could only be carried within locomotive bodies. In 1894, Hungarian engineer Kálmán Kandó developed a new type 3-phase asynchronous electric drive motors and generators for electric locomotives. Kandó's early 1894 designs were first applied in a short three-phase AC tramway in Évian-les-Bains (France), which was constructed between 1896 and 1898. In 1896, Oerlikon installed
8763-664: The Elder , were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A.D. that "it is easier to further the motion of a moving body than to move a body at rest". The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology , but the laws documented in his notebooks were not published and remained unknown. These laws were rediscovered by Guillaume Amontons in 1699 and became known as Amonton's three laws of dry friction. Amontons presented
8890-406: The approximation is its simplicity and versatility. Though the relationship between normal force and frictional force is not exactly linear (and so the frictional force is not entirely independent of the contact area of the surfaces), the Coulomb approximation is an adequate representation of friction for the analysis of many physical systems. When the surfaces are conjoined, Coulomb friction becomes
9017-435: The classic empirical model of friction (static, kinetic, and fluid) commonly used today in engineering. In 1877, Fleeming Jenkin and J. A. Ewing investigated the continuity between static and kinetic friction. In 1907, G.H. Bryan published an investigation of the foundations of thermodynamics, Thermodynamics: an Introductory Treatise dealing mainly with First Principles and their Direct Applications . He noted that for
9144-501: The contacting materials, such as surface roughness. The coefficient of friction is not a function of mass or volume. For instance, a large aluminum block has the same coefficient of friction as a small aluminum block. However, the magnitude of the friction force itself depends on the normal force, and hence on the mass of the block. Depending on the situation, the calculation of the normal force N {\displaystyle N} might include forces other than gravity. If an object
9271-628: The country lay within the hills and mountains of this region. After the Civil War , coal became one of Maryland's chief products and exports. Coal from the Cumberland area fueled the state's mills and plants , steamships in Baltimore 's harbor as well as the US Navy fleet, and was traded to buyers from London , Brazil , Egypt , and beyond. Primarily Scottish and Welsh immigrants provided
9398-433: The direction of the frictional force against a surface is opposite to the motion that surface would experience in the absence of friction. Thus, in the static case, the frictional force is exactly what it must be in order to prevent motion between the surfaces; it balances the net force tending to cause such motion. In this case, rather than providing an estimate of the actual frictional force, the Coulomb approximation provides
9525-433: The drive wheels of an accelerating car experience a frictional force pointing forward; if they did not, the wheels would spin, and the rubber would slide backwards along the pavement. Note that it is not the direction of movement of the vehicle they oppose, it is the direction of (potential) sliding between tire and road. The normal force is defined as the net force compressing two parallel surfaces together, and its direction
9652-430: The duty of a guard/train manager/conductor . Passenger trains are part of public transport and often make up the stem of the service, with buses feeding to stations. Passenger trains provide long-distance intercity travel, daily commuter trips, or local urban transit services, operating with a diversity of vehicles, operating speeds, right-of-way requirements, and service frequency. Service frequencies are often expressed as
9779-402: The end of the 19th century, because they were cleaner compared to steam-driven trams which caused smoke in city streets. In 1784 James Watt , a Scottish inventor and mechanical engineer, patented a design for a steam locomotive . Watt had improved the steam engine of Thomas Newcomen , hitherto used to pump water out of mines, and developed a reciprocating engine in 1769 capable of powering
9906-471: The end of the 19th century, improving the quality of steel and further reducing costs. Thus steel completely replaced the use of iron in rails, becoming standard for all railways. The first passenger horsecar or tram , Swansea and Mumbles Railway , was opened between Swansea and Mumbles in Wales in 1807. Horses remained the preferable mode for tram transport even after the arrival of steam engines until
10033-527: The engine by one power stroke. The transmission system employed a large flywheel to even out the action of the piston rod. On 21 February 1804, the world's first steam-powered railway journey took place when Trevithick's unnamed steam locomotive hauled a train along the tramway of the Penydarren ironworks, near Merthyr Tydfil in South Wales . Trevithick later demonstrated a locomotive operating upon
10160-475: The era of great expansion of railways that began in the late 1860s. Steel rails lasted several times longer than iron. Steel rails made heavier locomotives possible, allowing for longer trains and improving the productivity of railroads. The Bessemer process introduced nitrogen into the steel, which caused the steel to become brittle with age. The open hearth furnace began to replace the Bessemer process near
10287-459: The extent of the surface area; the normal pressure (or load); and the length of time that the surfaces remained in contact (time of repose). Coulomb further considered the influence of sliding velocity, temperature and humidity, in order to decide between the different explanations on the nature of friction that had been proposed. The distinction between static and dynamic friction is made in Coulomb's friction law (see below), although this distinction
10414-522: The first commercial example of the system on the Lugano Tramway . Each 30-tonne locomotive had two 110 kW (150 hp) motors run by three-phase 750 V 40 Hz fed from double overhead lines. Three-phase motors run at a constant speed and provide regenerative braking , and are well suited to steeply graded routes, and the first main-line three-phase locomotives were supplied by Brown (by then in partnership with Walter Boveri ) in 1899 on
10541-556: The force of gravity is perpendicular to the face of the plane. The normal force and the frictional force are ultimately determined using vector analysis, usually via a free body diagram . In general, process for solving any statics problem with friction is to treat contacting surfaces tentatively as immovable so that the corresponding tangential reaction force between them can be calculated. If this frictional reaction force satisfies F f ≤ μ N {\displaystyle F_{f}\leq \mu N} , then
10668-406: The force of static friction and causes sliding to occur. The instant sliding occurs, static friction is no longer applicable—the friction between the two surfaces is then called kinetic friction. However, an apparent static friction can be observed even in the case when the true static friction is zero. An example of static friction is the force that prevents a car wheel from slipping as it rolls on
10795-402: The forces required. Using ultrahigh vacuum and nearly zero temperature (5 K), a modified atomic force microscope was used to drag a cobalt atom, and a carbon monoxide molecule, across surfaces of copper and platinum . The Coulomb approximation follows from the assumptions that: surfaces are in atomically close contact only over a small fraction of their overall area; that this contact area
10922-489: The friction force always satisfies F f ≤ μ N {\displaystyle F_{f}\leq \mu N} , with equality reached only at a critical ramp angle (given by tan − 1 μ {\displaystyle \tan ^{-1}\mu } ) that is steep enough to initiate sliding. The friction coefficient is an empirical (experimentally measured) structural property that depends only on various aspects of
11049-486: The frictional heating is removed rapidly, the temperature drops, the pin remains solid and the COF rises to that of a 'low speed' test. In systems with significant non-uniform stress fields, because local slip occurs before the system slides, the macroscopic coefficient of static friction depends on the applied load, system size, or shape; Amontons' law is not satisfied macroscopically. Under certain conditions some materials have very low friction coefficients. An example
11176-441: The ground. Even though the wheel is in motion, the patch of the tire in contact with the ground is stationary relative to the ground, so it is static rather than kinetic friction. Upon slipping, the wheel friction changes to kinetic friction. An anti-lock braking system operates on the principle of allowing a locked wheel to resume rotating so that the car maintains static friction. The maximum value of static friction, when motion
11303-451: The highest possible radius. All these features are dramatically different from freight operations, thus justifying exclusive high-speed rail lines if it is economically feasible. Friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Types of friction include dry, fluid, lubricated, skin, and internal -- an incomplete list. The study of
11430-457: The inclined plane of successive asperities , then why is it not balanced through descending the opposite slope? Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, which should on the whole have the same tendency to accelerate as to retard the motion. In Leslie's view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before. In
11557-411: The interface between the materials, namely surface structure . For example, a copper pin sliding against a thick copper plate can have a COF that varies from 0.6 at low speeds (metal sliding against metal) to below 0.2 at high speeds when the copper surface begins to melt due to frictional heating. The latter speed, of course, does not determine the COF uniquely; if the pin diameter is increased so that
11684-728: The labor force for these mines, immigrating with their families for the opportunities America offered. In the Cumberland region, miners escaped the indebtedness to the mining company that plagued miners in surrounding states. The company store system, in which miners were forced to purchase all their supplies and household needs from the mining company, was outlawed in Maryland in 1868. A comparatively high proportion of miners were also homeowners, as local mining firms found it more profitable to sell houses to their miners, than establish "company" housing. Since regional coal mines were constructed with horizontal shafts, they were far less dangerous than
11811-1230: The limit being regarded at 200 to 350 kilometres per hour (120 to 220 mph). High-speed trains are used mostly for long-haul service and most systems are in Western Europe and East Asia. Magnetic levitation trains such as the Shanghai maglev train use under-riding magnets which attract themselves upward towards the underside of a guideway and this line has achieved somewhat higher peak speeds in day-to-day operation than conventional high-speed railways, although only over short distances. Due to their heightened speeds, route alignments for high-speed rail tend to have broader curves than conventional railways, but may have steeper grades that are more easily climbed by trains with large kinetic energy. High kinetic energy translates to higher horsepower-to-ton ratios (e.g. 20 horsepower per short ton or 16 kilowatts per tonne); this allows trains to accelerate and maintain higher speeds and negotiate steep grades as momentum builds up and recovered in downgrades (reducing cut and fill and tunnelling requirements). Since lateral forces act on curves, curvatures are designed with
11938-530: The linearity between static frictional force and normal force, found for typical Amonton–Coulomb type friction. The static friction force must be overcome by an applied force before an object can move. The maximum possible friction force between two surfaces before sliding begins is the product of the coefficient of static friction and the normal force: F max = μ s F n {\displaystyle F_{\text{max}}=\mu _{\mathrm {s} }F_{\text{n}}} . When there
12065-429: The locomotive-hauled train's drawbacks to be removed, since the locomotive need not be moved to the front of the train each time the train changes direction. A railroad car is a vehicle used for the haulage of either passengers or freight. A multiple unit has powered wheels throughout the whole train. These are used for rapid transit and tram systems, as well as many both short- and long-haul passenger trains. A railcar
12192-498: The long course of the development of the law of conservation of energy and of the first law of thermodynamics , friction was recognised as a mode of conversion of mechanical work into heat . In 1798, Benjamin Thompson reported on cannon boring experiments. Arthur Jules Morin (1833) developed the concept of sliding versus rolling friction. In 1842, Julius Robert Mayer frictionally generated heat in paper pulp and measured
12319-569: The main portion of the B&;O to the new line to New York through a series of tunnels around the edges of Baltimore's downtown. Electricity quickly became the power supply of choice for subways, abetted by the Sprague's invention of multiple-unit train control in 1897. By the early 1900s most street railways were electrified. The London Underground , the world's oldest underground railway, opened in 1863, and it began operating electric services using
12446-433: The mid-1920s. The Soviet Union operated three experimental units of different designs since late 1925, though only one of them (the E el-2 ) proved technically viable. A significant breakthrough occurred in 1914, when Hermann Lemp , a General Electric electrical engineer, developed and patented a reliable direct current electrical control system (subsequent improvements were also patented by Lemp). Lemp's design used
12573-409: The nature of friction in terms of surface irregularities and the force required to raise the weight pressing the surfaces together. This view was further elaborated by Bernard Forest de Bélidor and Leonhard Euler (1750), who derived the angle of repose of a weight on an inclined plane and first distinguished between static and kinetic friction. John Theophilus Desaguliers (1734) first recognized
12700-412: The noise they made on the tracks. There are many references to their use in central Europe in the 16th century. Such a transport system was later used by German miners at Caldbeck , Cumbria , England, perhaps from the 1560s. A wagonway was built at Prescot , near Liverpool , sometime around 1600, possibly as early as 1594. Owned by Philip Layton, the line carried coal from a pit near Prescot Hall to
12827-525: The possibility of a smaller engine that might be used to power a vehicle. Following his patent, Watt's employee William Murdoch produced a working model of a self-propelled steam carriage in that year. The first full-scale working railway steam locomotive was built in the United Kingdom in 1804 by Richard Trevithick , a British engineer born in Cornwall . This used high-pressure steam to drive
12954-437: The processes involved is called tribology , and has a history of more than 2000 years. Friction can have dramatic consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire . Another important consequence of many types of friction can be wear , which may lead to performance degradation or damage to components. It is known that frictional energy losses account for about 20% of
13081-408: The role of adhesion in friction. Microscopic forces cause surfaces to stick together; he proposed that friction was the force necessary to tear the adhering surfaces apart. The understanding of friction was further developed by Charles-Augustin de Coulomb (1785). Coulomb investigated the influence of four main factors on friction: the nature of the materials in contact and their surface coatings;
13208-405: The same materials. However, Richard Feynman comments that "with dry metals it is very hard to show any difference." The friction force between two surfaces after sliding begins is the product of the coefficient of kinetic friction and the normal force: F k = μ k F n {\displaystyle F_{k}=\mu _{\mathrm {k} }F_{n}} . This
13335-865: The so-called Painlevé paradoxes , may be encountered with Coulomb friction. Dry friction can induce several types of instabilities in mechanical systems which display a stable behaviour in the absence of friction. These instabilities may be caused by the decrease of the friction force with an increasing velocity of sliding, by material expansion due to heat generation during friction (the thermo-elastic instabilities), or by pure dynamic effects of sliding of two elastic materials (the Adams–Martins instabilities). The latter were originally discovered in 1995 by George G. Adams and João Arménio Correia Martins for smooth surfaces and were later found in periodic rough surfaces. In particular, friction-related dynamical instabilities are thought to be responsible for brake squeal and
13462-441: The standard for railways. Cast iron used in rails proved unsatisfactory because it was brittle and broke under heavy loads. The wrought iron invented by John Birkinshaw in 1820 replaced cast iron. Wrought iron, usually simply referred to as "iron", was a ductile material that could undergo considerable deformation before breaking, making it more suitable for iron rails. But iron was expensive to produce until Henry Cort patented
13589-435: The temperature rise. In 1845, Joule published a paper entitled The Mechanical Equivalent of Heat , in which he specified a numerical value for the amount of mechanical work required to "produce a unit of heat", based on the friction of an electric current passing through a resistor, and on the friction of a paddle wheel rotating in a vat of water. Osborne Reynolds (1866) derived the equation of viscous flow. This completed
13716-456: The tentative assumption was correct, and it is the actual frictional force. Otherwise, the friction force must be set equal to F f = μ N {\displaystyle F_{f}=\mu N} , and then the resulting force imbalance would then determine the acceleration associated with slipping. The coefficient of friction (COF), often symbolized by the Greek letter μ ,
13843-475: The time, was Liverpool and Manchester Railway , built in 1830. Steam power continued to be the dominant power system in railways around the world for more than a century. The first known electric locomotive was built in 1837 by chemist Robert Davidson of Aberdeen in Scotland, and it was powered by galvanic cells (batteries). Thus it was also the earliest battery-electric locomotive. Davidson later built
13970-428: The total energy expenditure of the world. As briefly discussed later, there are many different contributors to the retarding force in friction, ranging from asperity deformation to the generation of charges and changes in local structure . Friction is not itself a fundamental force , it is a non-conservative force – work done against friction is path dependent. In the presence of friction, some mechanical energy
14097-543: The track. Propulsion for the train is provided by a separate locomotive or from individual motors in self-propelled multiple units. Most trains carry a revenue load, although non-revenue cars exist for the railway's own use, such as for maintenance-of-way purposes. The engine driver (engineer in North America) controls the locomotive or other power cars, although people movers and some rapid transits are under automatic control. Traditionally, trains are pulled using
14224-471: The transport of ore tubs to and from mines and soon became popular in Europe. Such an operation was illustrated in Germany in 1556 by Georgius Agricola in his work De re metallica . This line used "Hund" carts with unflanged wheels running on wooden planks and a vertical pin on the truck fitting into the gap between the planks to keep it going the right way. The miners called the wagons Hunde ("dogs") from
14351-417: The two coefficients are equal, such as teflon-on-teflon. Most dry materials in combination have friction coefficient values between 0.3 and 0.6. Values outside this range are rarer, but teflon , for example, can have a coefficient as low as 0.04. A value of zero would mean no friction at all, an elusive property. Rubber in contact with other surfaces can yield friction coefficients from 1 to 2. Occasionally it
14478-573: The valley between 1876 and 1917, followed by the Western Maryland Railway . Most of the original settlers to the Valley came in response to the abundance of jobs available in the coal mines. Many were Irish , but German , Scottish , and Welsh names also are found in the early records of the town. Coal mining quickly became the most important industry in the Cumberland area . Some of the richest beds of soft, bituminous coal in
14605-559: The valley every day, but now do so only once or twice a month. [REDACTED] Georges Creek is pronounced Georges crick by locals, though they pronounce other streams as creek . Heavy Scottish heritage in the area give locals a dialect unique in the area. Many outsiders confuse the local dialect with that of Ontario , Canada, which it closely resembles. 39°34′18″N 78°58′38″W / 39.57167°N 78.97722°W / 39.57167; -78.97722 Railroad Rail transport (also known as train transport )
14732-402: The value F f = μ N {\displaystyle F_{f}=\mu N} . Until then, friction is whatever it needs to be to provide equilibrium, so it can be treated as simply a reaction. If the object is on a tilted surface such as an inclined plane, the normal force from gravity is smaller than m g {\displaystyle mg} , because less of
14859-629: The wheels on track. For example, evidence indicates that a 6 to 8.5 km long Diolkos paved trackway transported boats across the Isthmus of Corinth in Greece from around 600 BC. The Diolkos was in use for over 650 years, until at least the 1st century AD. Paved trackways were also later built in Roman Egypt . In 1515, Cardinal Matthäus Lang wrote a description of the Reisszug ,
14986-622: The world in 1825, although it used both horse power and steam power on different runs. In 1829, he built the locomotive Rocket , which entered in and won the Rainhill Trials . This success led to Stephenson establishing his company as the pre-eminent builder of steam locomotives for railways in Great Britain and Ireland, the United States, and much of Europe. The first public railway which used only steam locomotives, all
15113-512: Was a soft material that contained slag or dross . The softness and dross tended to make iron rails distort and delaminate and they lasted less than 10 years. Sometimes they lasted as little as one year under high traffic. All these developments in the production of iron eventually led to the replacement of composite wood/iron rails with superior all-iron rails. The introduction of the Bessemer process , enabling steel to be made inexpensively, led to
15240-602: Was accomplished by the distribution of weight between a number of wheels. Puffing Billy is now on display in the Science Museum in London, and is the oldest locomotive in existence. In 1814, George Stephenson , inspired by the early locomotives of Trevithick, Murray and Hedley, persuaded the manager of the Killingworth colliery where he worked to allow him to build a steam-powered machine. Stephenson played
15367-412: Was already drawn by Johann Andreas von Segner in 1758. The effect of the time of repose was explained by Pieter van Musschenbroek (1762) by considering the surfaces of fibrous materials, with fibers meshing together, which takes a finite time in which the friction increases. John Leslie (1766–1832) noted a weakness in the views of Amontons and Coulomb: If friction arises from a weight being drawn up
15494-514: Was built by Siemens. The tram ran on 180 volts DC, which was supplied by running rails. In 1891 the track was equipped with an overhead wire and the line was extended to Berlin-Lichterfelde West station . The Volk's Electric Railway opened in 1883 in Brighton , England. The railway is still operational, thus making it the oldest operational electric railway in the world. Also in 1883, Mödling and Hinterbrühl Tram opened near Vienna in Austria. It
15621-706: Was built in 1758, later became the world's oldest operational railway (other than funiculars), albeit now in an upgraded form. In 1764, the first railway in the Americas was built in Lewiston, New York . In the late 1760s, the Coalbrookdale Company began to fix plates of cast iron to the upper surface of the wooden rails. This allowed a variation of gauge to be used. At first only balloon loops could be used for turning, but later, movable points were taken into use that allowed for switching. A system
15748-548: Was introduced in which unflanged wheels ran on L-shaped metal plates, which came to be known as plateways . John Curr , a Sheffield colliery manager, invented this flanged rail in 1787, though the exact date of this is disputed. The plate rail was taken up by Benjamin Outram for wagonways serving his canals, manufacturing them at his Butterley ironworks . In 1803, William Jessop opened the Surrey Iron Railway ,
15875-489: Was light enough to not break the edge-rails track and solved the problem of adhesion by a cog-wheel using teeth cast on the side of one of the rails. Thus it was also the first rack railway . This was followed in 1813 by the locomotive Puffing Billy built by Christopher Blackett and William Hedley for the Wylam Colliery Railway, the first successful locomotive running by adhesion only. This
16002-762: Was tested on the Edinburgh and Glasgow Railway in September of the following year, but the limited power from batteries prevented its general use. It was destroyed by railway workers, who saw it as a threat to their job security. By the middle of the nineteenth century most european countries had military uses for railways. Werner von Siemens demonstrated an electric railway in 1879 in Berlin. The world's first electric tram line, Gross-Lichterfelde Tramway , opened in Lichterfelde near Berlin , Germany, in 1881. It
16129-580: Was the first tram line in the world in regular service powered from an overhead line. Five years later, in the U.S. electric trolleys were pioneered in 1888 on the Richmond Union Passenger Railway , using equipment designed by Frank J. Sprague . The first use of electrification on a main line was on a four-mile section of the Baltimore Belt Line of the Baltimore and Ohio Railroad (B&O) in 1895 connecting
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