cahya/simple-wikipedia huggingface dataset:
A collision occurs when two objects come in contact with each other. All collisions have the same momentum before and after a collision. Examples of collisions include car crashes, bouncing a ball, and playing pool. Collisions are made from two smaller sections called elastic and inelastic collisions.

Elastic Collisions 

In the case of playing pool or bouncing a ball, an elastic collision occurs. An elastic collision generally occurs when an elastic or hard object experiences a collision that bounces off another elastic or hard object, where the kinetic energy and momentum are the same before and after the collision. In an experiment, a small amount of energy will still be lost because of the friction between the surface and the objects.

Inelastic Collisions 
In the case of a car crash, an inelastic collision occurs. An inelastic collision generally occurs when a soft object experiences a collision that does not result in a bounce. Kinetic energy is lost during this type of collision because the energy is transformed into other forces. The momentum is the same before and after the collision.

Two Dimensional Collisions 
In the case of a two dimensional collision, the rules in elastic and inelastic collision are still the same, but vectors are used to find the momentum before or after a collision.

Sources 
Duncan, Tom. Advanced Physics for Hong Kong: Volume 1 Mechanics & Electricity. John Murray Ltd, 1995.
Wai, Loo Kwok. Longman A-Level Course in Physics: Volume 1. Pearson Education South Asia Pte Ltd, 2003.

Mechanics
Belgrade is the capital city of the country of Serbia. Before the wars of the 1990s, it was the capital of Yugoslavia.

Belgrade is also one of the most popular travel destinations in Southeastern Europe. It is famous for a very busy nightlife and a lot of entertainment activities.

The main tourist attractions in Belgrade are:
 Kalemegdan Fortress
 Knez Mihailova Street
 Belgrade Zoo
 Memorial Complex "Josip Broz Tito"

History 
The first settlements on the city's territory date back to Vinča cutlure. The city itself (under the name Singidunum) was founded by the Celtic Scordis tribe in the 3rd century BC. Then it was owned by the Romans, Byzantines, Avars, Slavs, etc. In 878 it was first mentioned as Belgrade. In 1403 it became the Serbian capital. In 1521, the city was conquered by the troops of the Ottoman Empire. In 1815 it again became the capital of Serbia. From 1918 to 2003 it was the capital of Yugoslavia. In 2003-2006, Belgrade was the unofficial capital of the confederal union of the two states of Serbia and Montenegro.

Related pages 
 Belgrade Philharmonic Orchestra

Other websites 

 WorldFlicks in Belgrade: Photos and interesting places on Google Maps
A hydrogen economy is a hypothetical future economy in which the primary energy used for automobiles and other vehicles as well as creating electricity comes from hydrogen and renewable energy sources, like windmills and solar panel.

Purpose 
The reason to use this is to replace the use of petroleum. It would also stop the use of fossil fuels which causes carbon dioxide along with many other greenhouse gases, such as carbon monoxide and methane, to be created. These float up into the atmosphere, damaging it. This is bad for the ecology.

Hydrogen
Economics
Energy
A barnacle is a cirripede, a kind of crustacean. It is covered with hard plates of calcium carbonate, and lives stuck to hard surfaces.

It does not look like a crustacean, and for many centuries it was thought to be a mollusc. In the 1830s, J.V. Thompson found their larvae, and followed their development through to their adult form. They have a nauplius larva, typical of crustaeans. Later Charles Darwin, who spent eight years working on barnacles, found that Thompson had been right.

Barnacles grow on hard surfaces like piers, boats, rocks, and on other animals such as turtles and whales. Barnacles are a different group from crabs and shrimps. They are considered a nuisance to the shipping industry and private boat owners.

Life-style 
Barnacles are suspension feeders, sweeping small food into their mouth with their curved 'feet'. They are cemented to rock (usually), and covered with hard calcareous plates, which they shut firmly when the tide goes out. The barnacles reproduce sexually, and produce little nauplius larvae which disperse in the plankton. Eventually, the larvae change into cypris form, and attach on other hard surfaces to form new barnacles. Their comparative anatomy was worked out in detail by Charles Darwin.

Reproduction 
Barnacles have the largest penis to body size ratio of the animal kingdom. A few forms have become fully parasitic on larger crustacea.

Barnacles are by far the commonest animals on rocky sea shores. Their numbers on a shore in the Isle of Man have been estimated as a thousand million (109), and they produce body material of 12 hundrededweight (~600 kg) of tissue, weighed after drying. Each year they let go a huge number of larvae, estimated as a million million (1012).p110

Darwin's work 
Darwin set his work out in four parts: There were the barnacles on stalks (pedunculated), and those that sat on hard substrate (the sessile barnacles). Each of these was divided into living and fossil barnacles.
1851: A Monograph of the Sub-class Cirripedia, with figures of all the species. The Lepadidae; or, Pedunculated Cirripedes. Living barnacles. 
1851: A Monograph on the Fossil Lepadidae, or, Pedunculated Cirripedes of Great Britain. Fossil barnacles. 
1854: A Monograph of the Sub-class Cirripedia, with figures of all the species. The Balanidae (or Sessile Cirripedes); the Verrucidae, etc. 
1854: A Monograph on the Fossil Balanidæ and Verrucidæ of Great Britain

Gallery

References 

Crustaceans
In Greek mythology, Odysseus was the great grandson of the Greek god Hermes. He was the king of the island Ithaca. He was married to Penelope. Odysseus and Penelope had a son called Telemachos. Odysseus is a major character in Homer's Iliad and Odyssey.

Odysseus fought in the Trojan War. He invented the Trojan Horse, which helped the Greeks win the war. After the war, his adventurous journey home took 10 years. The story of that journey is told in the Odyssey. Odysseus angered Poseidon, the god of seas, when he half blinded his cyclops son Polyphemos. In anger, Poseidon stopped him from leaving the island. The Latin name for Odysseus is "Ulysses".

There have been many movies about Odysseus, because of his heroic and intelligent battle strategies.

Other websites

Odysseus
Adult Swim (stylized as [adult swim] or shortened to [as]) is an American adult-oriented nighttime programming block of the basic cable network Cartoon Network that is programmed by its in-house production studio, Williams Street. Marketed as a separate network for ratings purposes, Adult Swim broadcasts nightly from 8 p.m. to 6 a.m. ET/PT.

Debuting in 2001, Adult Swim serves as the nighttime identity of Cartoon Network, and it was established as alternative programming during late night hours when Cartoon Network's primary target audience would normally be sleeping. By 2005, Adult Swim would be granted its own separate Nielsen ratings report from Cartoon Network due to it targeting a different audience. The block features stylistically varied animated and live-action shows, including original programming, syndicated series, anime, original video animations, and short films with generally minimal or no editing for content.

Adult Swim has frequently aired adult animation features, mockumentaries, sketch comedy, and pilots. The block's shows are known for their sexual themes, frank sexual discussion, nudity, strong language, and graphic violence. Many of its programs are aesthetically experimental, transgressive, improvised, and surrealist in nature. Adult Swim has contracted with various studios known for their productions in absurd and shock comedy.

References

2001 establishments in California
Adult Swim
American television networks
American television series
American television stations
Time Warner subsidiaries
WESC is a Swedish company. The company makes clothing, like jeans and shirts.  Many people like these clothes, and they can buy them in many countries, for example in the United States, Japan and Germany. Because some famous people use the clothes, other people want to buy them too.

Companies of Sweden
Clothing companies
Yarmouth is a town in the province of Nova Scotia in the country of Canada. In 2011, the population of Yarmouth was 6,761.

References

Other websites 
Yarmouth official town government Website 

Towns in Nova Scotia
The spleen is an organ in vertebrates. The spleen is part of the lymphatic system. In people, it is on the left side of the body, under the heart. The spleen helps fight infections and keeps the blood cells healthy.

Tasks 
The spleen cleans out old blood cells from the blood and recycles them. It helps save the iron and the amino acids from the old blood cells. The spleen also holds a supply of extra blood, in case the body needs some quickly. The spleen works together with the circulatory system (the system which brings blood to the body).

A study published in 2009 using mice found that the spleen is a reservoir which holds over half the body's monocytes. These monocytes move to injured tissue (such as the heart after myocardial infarction), turn into dendritic cells and macrophages, and promote tissue healing. The spleen is rather like a large lymph node. Its absence makes certain infections more likely.

Shape 
The spleen is shaped like a loose fist. It is tucked under the left side of the diaphragm, close by the heart.The average adult spleen weighs 0.44 lbs.

Disease 
The spleen can get bigger when a person is digesting food or is sick. If a person's spleen gets big enough, it can break open. If this happens, the person needs medical care right away. Emergency surgery might be needed to control the bleeding.

Some of the diseases that cause the spleen to get bigger are:  
 malaria, 
 rheumatoid arthritis, 
 systemic lupus, 
 sickle cell anemia, 
 leukemia, 
 lymphoma, and 
 mononucleosis ("mono").

Culture 
In the past, many people believed the spleen helped control emotions. For example, if a person was upset or angry, people would think it was because of a spleen problem.

References

Glands
Lymphatic system
The placenta is a temporary organ found in eutherian female mammals while they are pregnant.  

The placenta is connected to the fetus by the umbilical cord, which is made of blood vessels and connective tissue. When the fetus is delivered, the placenta is delivered afterwards. The placenta is often called the afterbirth.

Function

The placenta protects the mother and fetus 
One of the placenta's jobs is to make sure blood from the mother and fetus never mixes. The placenta acts as an exchange surface between the mother and the fetus. Nutrients and oxygen are passed over by diffusion only. If the mother's and fetus's blood mixed, it could be deadly for both of them. If the mother and the fetus had different blood types, they might both die if their blood mixed.

The placental barrier protects the fetus 
The placenta has two parts, one of which is genetically and biologically part of the fetus, the other part of the mother. It is implanted in the wall of the uterus, where it receives nutrients and oxygen from the mother's blood and passes out waste. This forms a barrier called the placental barrier, which filters out some substances which could harm the fetus. 

However, the placental barrier is not able to protect the fetus from everything that could hurt it.  For example, alcohol goes through the placental barrier into the fetus.  This is why drinking alcohol during pregnancy can cause Fetal Alcohol Syndrome.  The placenta is also unable to filter out many other things.  Chemicals that can cross the placental barrier and hurt the fetus are called teratogens. 

Some infectious diseases may also cross this barrier and infect the fetus.

In other types of mammals 
Prototherial (egg-laying) and metatherial (marsupial) mammals produce a type of placenta that provides nutrients mostly from the egg sac, instead of from the mother's blood. It is positioned in the female's body similar to eutherian mammals. Some snakes and lizards have evolved a system of internal development with a placenta-like tissue: this is an example of convergent evolution.

References 

Pregnancy and childbirth
Urbana is a city in the U.S. state of Illinois. It is the twin city of Champaign, Illinois and is separated by a single street.  The main campus of the University of Illinois is in Urbana and Champaign. As of 2019, it has population of 42,214.

Population 
Population (2010) • City 41,250

Estimate (2016) 42,014
Density 3,552.08/sq mi (1,371.49/km2) 
Metropolita area 231,891

References 

cities in Illinois
county seats in Illinois
William Edgar (Bill) Oddie OBE (born 7 July 1941) is a British comedian, actor, writer and television personality. 

Oddie was born in Rochdale, Lancashire and grew up in Birmingham. He read English Literature at Pembroke College, Cambridge where he gained an MA. He is most famous for his birdwatching and conservation work. In the 1970s, he was a member of the BBC One television comedy series, The Goodies. Doctors found that his mother, Lilian, had schizophrenia. Oddie says that he does not remember her living at home because she spent a lot of her life in mental hospitals.

Oddie has bipolar disorder.

References

Other websites 
Official website

1941 births
Living people
Actors from Birmingham
Actors from Lancashire
Alumni of the University of Cambridge
Comedians from Lancashire
English movie actors 
English television actors
English television presenters
English television writers
People with bipolar disorder
People from Rochdale
Television personalities from Lancashire
Writers from Birmingham
Writers from Lancashire
Montgomery Ward was an American department store chain. It currently exists only as an online retail website since 2004. It only delivers in the United States. 

It started as a mail-order catalog (called a "Wish Book") and department store in 1872. It owned Jefferson Ward discount stores. Jefferson Ward stores in the northern US were sold to Bradlees in 1985. The rest closed in 1988. All its stores closed in 2000. In 2004, it reopened as an online store.

Montgomery Ward was founded by Aaron Montgomery Ward, a Chicago entrepreneur.

References 

American department stores
1872 establishments in the United States
2001 disestablishments in the United States
Companies based in Illinois
Chicago, Illinois
Raptor can mean:
 Birds of prey, the group of birds which includes eagles, hawks, and falcons.
 Feathered dinosaurs of the Dromaeosaur family, including Velociraptor and Deinonychus
 F-22 Raptor fighter jet
 The Toronto Raptors, a National Basketball Association team that play in Toronto, Ontario
This is about the sport. You may be wanting to read about a fence.

Fencing is a sport that includes two people with swords. The aim is to score hits. There is also a referee.
In the olden times when two people argued they fenced the first one to draw blood was wrong and the person would be dead, so the person that won would claim the dead person's house and belongings.

Weapons

Foil 

The foil is a light and easy to bend weapon, first made in mid 17th century as a weapon for practice. 'Hits' can only be scored by hitting the target area with the point of the sword. The target area is the torso.

Épée 

The épée is the heaviest of the three weapons. To score a hit, the push-button on the end of the weapon must remain fully down for 2-10 milliseconds, and must arrive (hit) with a force of at least 7.35 newtons. The target area for Épée is the entire body. This includes the feet and the head.

Sabre 

The sabre is the "cutting" weapon, with a curved guard (to protect the hand) and a triangular blade. However, in modern electric scoring, a touch with any part of the sabre, (point, flat or edge, as long as it is on target) will count as a hit. The target area in sabre is everything from the waist up, except for the hands.

Uniform 
Fencers wear a uniform to avoid injury. They wear a mask of black mesh with a bib. Also, a jacket, short pants and a sort of half-a-shirt (called an underarm protector or plastron), all of white fabric. They must also wear socks that cover their legs. Women must wear a chest protector. These are collectively called "whites."

Other websites 

 Fédération Internationale d'Escrime The organisation responsible for all international fencing

Fencing
Administrators are people who organize things like businesses.  All businesses have administrators.  They make decisions, organize the people who work there and make sure that things are working alright and there are no problems. Their work is called "administration". The administrators are part of the "management".

An administrator is also the person in charge of some of the small territories of the United Kingdom,  for example Ascension Island and the British Antarctic Territory which are too small to run their own government.

Internet
Occupations
The Hague (with capital T; Dutch: also called , commonly ) is the third-largest city in the Netherlands, after Amsterdam and Rotterdam. It has a population of about 546,000 (2020) and an area of around 98 km². It is in the west of the country, in the province South Holland. It is the capital of the province. About 1 million people live in the urban area of The Hague, on about 405 square kilometers.

The Hague is the location of the Binnenhof, the building where the national government of the Netherlands meets. Built in the 13th century, the Binnenhof is the home of the "Eerste Kamer" (literally "First Chamber") or "Senaat", and the "Tweede Kamer" (literally "Second Chamber"). These are the same as the upper and lower houses in some other countries. They form the "Staten Generaal" (literally the "Estates-General").

Willem-Alexander, the king of the Netherlands, lives and works in The Hague. His home is called the Noordeinde Palace and it is not far away from the Binnenhof. All foreign embassies and government ministries of the country are in the city, as well as the Hoge Raad der Nederlanden (The Supreme Court) and many lobbying organisations.

All of this is unusual for a country, because The Hague is not the capital of the Netherlands, which is Amsterdam. This is made so by the Constitution of the Netherlands.

Besides the buildings used by the government, the International Court of Justice of the United Nations is based in the Peace Palace, which is also in The Hague and often referred to as "The Hague" by metonymy. A tourist attraction is Madurodam, which has lots of tiny buildings that look like the real things.

The Hague is part of a large conurbation called the Randstad, where most Dutch people live. It is only an hour away from Amsterdam, Utrecht, and Amsterdam Airport Schiphol by train (most of which are run by Nederlandse Spoorwegen) and with its two train stations, is easy to get to from many places in the Netherlands and all around Europe.

Partner cities 
 Warsaw, Poland

Things to see

Related pages
Residentie Orchestra

References

 
Cities in the Netherlands
Settlements in South Holland
Provincial capitals of the Netherlands
The S.A.S. or Special Air Service, is a Special Operations Organisation of the British Army. It was founded in 1941 to attack behind the German line of defence in North Africa, in World War II. They are one of the best schooled units in the world, that makes them very valuable. There are about 500 active SAS soldiers.

The SAS is a secret organisation. Its members often do not tell anyone except close family that they are in it. The British Ministry of Defence (MOD) rarely speaks of the SAS and mission details are never released until much later.

The badge of the organisation is a flaming excalibur. It shows the motto: Who Dares Wins.

Current SAS roles include:

 Gathering intelligence behind enemy lines.
 Destroying targets far behind enemy lines.
 Protecting The Royal Family, and important government members.
 Training special forces of other nations.
 Performing counter-terrorism operations.

The SAS is thought of all over the world as one of the best, if not the best Special Operations organisations.
This is mainly because of the intense training they are put through. The hardest part of this is intense interrogation (questioning while under torture) which the trainees must go through.

The SAS is respected worldwide and used to train many other Special Forces Units. Several special operations units are modeled after the SAS. For example, the U.S. Army's Delta Force was founded due in large part to Charles Beckwith, a U.S. Army special operations officer, serving as an exchange officer with the SAS. He felt that the U.S. Army was vulnerable in not having a unit comparable to the SAS.

Related pages
 Central Intelligence Agency
 Secret Intelligence Service
 Special forces

Sources 

1941 establishments in Europe
Military of the United Kingdom
Special Forces
1940s establishments in the United Kingdom
Lancashire is a ceremonial county in the North West of England. Its two cities are Lancaster and Preston. Before 1974, Liverpool and Manchester were part of administrative county of Lancashire.

Rivalry
The county has developed a fierce rivalry with Yorkshire, the next county east. This comes from rivalry in sport, such as in cricket, and comes from the War of the Roses.

Places
A big attraction in Lancashire is Blackpool, an English seaside resort, which has a theme park called Blackpool Pleasure Beach. It has the second largest rollercoaster in Europe ("The Big One") and Blackpool Tower, a tower which was made to look like the Eiffel Tower in Paris.

Lancashire has market towns (like Chorley) and small villages (like Bretherton, Croston and Eccleston). It is just south of an area of outstanding natural beauty called the Lake District. Lancashire also has a lot of pleasant countryside such as White Coppice and the Rivington Moors.

Food
A famous food from Lancashire is "Lancashire Hot pot" which is made of meat, onion or other vegetables and potatoes. It is often found on many pub menus in the county and in other places in Britain.

People
The people of Lancashire are known for their friendly nature. Humour is also an important part of Lancashire life.

Ceremonial counties of England
The Church of England is the leading Christian church in England. It is the church established by law: its formal head is the English monarch (Elizabeth II). It is the mother church of the Anglican Communion. Its headquarters are at Church House, Westminster, in London.

The Church of England understands itself to be both Catholic and Reformed:
Catholic because it views itself as a part of the universal church of Jesus Christ in unbroken continuity with the early apostolic church. This is expressed in its emphasis on the teachings of the early Church Fathers, as in the Apostles' Creed, Nicene Creed and Athanasian Creed.
Reformed because it has been shaped by the doctrinal ideas of the 16th-century Protestant Reformation, in particular by the Thirty-Nine Articles and the Book of Common Prayer.

There are other Protestant churches in England which are not part of the Anglican Communion.

History 
The Church of England became independent under King Henry VIII in 1534. Henry VIII was married to Catherine of Aragon, but asked the Pope to annul the marriage (say that it was a mistake and that Henry and Catherine were never really married).  He wanted to annul the marriage because he wanted a male heir to his throne and Catherine could not produce one. When the annulment was refused, Henry VIII used his position as King to break the Church away from the Roman Catholic Church. This established the independence of the Church of England, sometimes called the Anglican (English) Church. Methodism broke away from the church in the 18th century. The Oxford Movement brought some Catholic beliefs and practices back into the church in the 19th century. 

Under his son, King Edward VI, more Protestant forms of worship were adopted. The Archbishop of Canterbury, Thomas Cranmer started more changes. A new pattern of worship was set out in the Book of Common Prayer (1549 and 1552). These were based on the older liturgy but influenced by Protestant principles.

Related pages 
Archbishop of Canterbury
Thomas Cranmer
Reformation
House of Lords

Other websites 
CofE website

Anglicanism
England
Tense is the form of a verb that shows the time something happened, or is going to happen. There are three main tenses:

Present tense: things that are true when the words are spoken or written.
Example: She goes to school. In this sentence, goes shows that it is a present tense. It suggests that she regularly goes to school.
Example: She is going to school. This says she is now going to school.
Past tense: things that were true before the words were spoken or written. 
Example: She went to school. In this sentence, went shows that it is a past tense.
Future tense: things that will be true after the words are spoken or written. 
Example: She will go to school. In this sentence, will shows that it is a future tense.

Tense can be shown by changing the spelling of a verb. For example, be can become am, is, and are in present tense, and was and were in past tense. In English, future tense is shown by adding will before the verb. For example, be becomes will be in future tense.

Note:These tenses can be subdivided further (see below).

Aspect 
There are also different kinds of tense within each main tense. They are formed by adding "helping words" or "auxiliary words", such as be and have, before the verb. For example, "I give", "I have given", "I am giving", and "I have been giving" are all in present tense, but have different meanings. This is called aspect. 

Other languages have different ways of showing tense. For example, Latin usually shows tense by changing the verb, like English. However, Chinese and Indonesian show tense by adding new words, instead of changing the verb.

References 

Grammar
Blackpool Tower is a tall structure in Blackpool, a North England seaside town.

It was built in the style of the Eiffel Tower. Building started in 1891 and finished in 1894. It cost £45000 (around US$70000), is 518 ft tall and weighs 2586 tons. It is mainly made from steel and cast iron.

It is one of the main tourist attractions in Blackpool. These include the tower itself, the Golden Mile, which is a row of arcades, the Irish Sea and beach, and Pleasure Beach Blackpool (a theme park).

The oldest part of the building is the old aquarium which was part of Dr Cockers' Menagarie and Aquarium since the 1870s. It was kept open to earn money while the tower building was built around it.

The tower was bought by Blackpool Council in 2010 and is now run by Merlin Entertainments for Blackpool Council.

Since Merlin Entertainments started running the tower, the building has been repaired and new attractions have been added. The aquarium was removed to make way for a new attraction.

Attractions at the tower include the Blackpool Dungeon, the Blackpool Tower Eye, the Blackpool Tower Circus, the Blackpool Tower Ballroom and Jungle Jim's.

References

1894 establishments in the United Kingdom
Blackpool
Monuments and memorials in England
Towers in the United Kingdom
Buildings and structures completed in the 19th century
Kookaburras are birds of the genus Dacelo and are native to Australia and New Guinea. An adult kookaburra is generally 28–42 centimetres from the head to the tip of the tail.

Taxonomy 

 Genus Dacelo
 Laughing Kookaburra (Dacelo novaeguineae) – Native to eastern mainland Australia, introduced to Tasmania, Flinders Island, Kangaroo Island and Western Australia. Some were also introduced to New Zealand between 1866 and 1880; but only those that were freed by Sir George Grey on Kawau Island are still there today.
 Blue-winged Kookaburra (Dacelo leachii) – Native to northern Australia and southern New Guinea.
 Spangled Kookaburra (Dacelo tyro) – Found only on the Aru Islands and Trans Fly savanna and grasslands of southern New Guinea.
 Rufous-bellied Kookaburra (Dacelo gaudichaud) – Widely distributed through forests of lowland New Guinea and has also been seen on Saibai Island in Queensland.

Life 
Kookaburras usually eat small animals: small mammals (like mice), insects, small birds, lizards and snakes. 

Kookaburras usually live in family groups. Young kookaburras help their parents to hunt and care for the smaller children.

Kookaburras are well known for their loud call, which sounds a bit like human laughter. Kookaburras use their calling to show others what is their land.

Coraciiformes
Birds of Australia
Birds of Oceania
Poll tax is a system of taxing. It is also called head tax. It is based on the idea that everyone pays the same amount of tax. This is regardless of how much they earn. In the last few years of Margaret Thatcher's reign as British Prime minister, she received heavy opposition and mass riots were held when she tried to have poll tax used as the tax system.

Taxation
CONMEBOL Libertadores or Copa Libertadores (Libertadores Cup) is a football competition between the best club teams in South America. The teams are qualified based on how well they did in the national tournament. The last year winner has assured participation. The tournament is run by Confederación Sudamericana de Fútbol (CONMEBOL).

Schedule
Copa Libertadores is played annually. It usually happens between the months of February and November (South American summer and spring). Its winner is qualified for the annual FIFA Club World Cup.

Libertadores starts in January with the worst classified team of each country playing for to be a part of the "Main Draw". In February, the Main Draw begins. It is made up of 8 groups with 4 clubs in each group. Each team plays 6 games. They play three home games and three away games. The top 2 clubs in every group advance to the next round. A total of 16 clubs play in the playoffs.

The better qualified clubs in the Main Draw take advantage of playing the second game of each round of the playoffs at home. Libertadores goes on with clubs playing home and away, round after round till the Finals.

Differences
Unlike European club competitions, the Copa Libertadores, in the past, did not use extra time or away goals to decide a tie. Starting with the 2005 event, CONMEBOL began to use the away goals rule, with the extra time used only in the final matches.

Football competitions in South America
CONMEBOL
A longbow is a type of bow. It may not have been as powerful as a crossbow but it could shoot more arrows per minute. Also, the basic equipment cost little, and could be easily mass produced. Metal-tipped arrows could pierce all but the best plate armour. Archers (longbowmen) would usually have a second weapon, often a battle-axe, for close-quarter fighting.

The longbow was mainly used in the Middle Ages until Henry VIII's reign.  

It was made from a single piece of hard wearing, flexible wood (often yew). Yew was cut during the winter when there was no sap. The flat side of the bow facing the target was flexible sapwood while the belly (facing the archer) was round and made of strong heartwood (from the center of a tree). The devastating hail of the longbowmen (at a rate of six per minute) was often very demoralizing. 
Longbows have been found in Europe as far back as the Mesolithic period.

History 
In the British Isles the weapon was first recorded as being used by the Welsh. In AD 633 Offrid, son of Edwin, king of Northumbria, was killed by an arrow shot from a Welsh longbow. This was during a battle between the Welsh and the Mercians — more than five centuries before any record of its use in England. Despite this, the weapon is more commonly known as the "English longbow" than the "Welsh longbow".

In the Middle Ages the English and Welsh were famous for their very powerful Welsh longbows. They were used to great effect in the civil wars of the period and against the French in the Hundred Years' War (with notable success at the battles of Crécy (1346), Poitiers (1356) and Agincourt (1415).

The average length of arrowshafts recovered from the 1545 sinking of the Mary Rose is .

A longbow has practical advantages compared to a modern recurve or compound bow; it is usually lighter, quicker to prepare for shooting, and shoots more quietly. However, other things being equal, the modern bow will shoot a faster arrow more accurately than the longbow.

References 

Archery
Weapons
The African Union (AU) is an supranational organization consisting of fifty-five African member countries. Founded in Durban on 9 July 2002, the AU was formed as a replacement to the Organization of African Unity (OAU) and the African Economic Community (AEC). 

The current Chairperson of the African Union is President of Senegal Macky Sall since February 5, 2022.

The AU, in the future, aims to have a single currency and a single integrated defense force, as well as other institutions of state, including a cabinet for the AU Head of State. The purpose of the organization is to help secure the continent's democracy, human rights, and a sustainable economy, especially by bringing an end to conflict between African nations and creating an effective common market.

Related pages
 African Charter on Human and Peoples' Rights
 European Union

Other websites 
 Official site

International organizations
2002 establishments
Politics of Africa
2000s establishments in Africa
The Freecycle Network (TFN) is a global network of people who share and regive items. They organise their network through the Internet. Freecycle is a place for people to meet. There are just two things people can do there.

The first thing is this:  A person can ask the other people for an item.  If someone has it, they can tell the person who wants it.

The second thing is this: A person can give away an item.  Sometimes many people want the item, and the donator has to choose just one person.

Other websites 
Official website
Freecycle Group Finder

Internet
Slashdot is a website where people can read news.  Most people who go to Slashdot like computers.  Other people go, too.

On the Slashdot website, people can comment on the news. Often this leads to interesting discussions with many points of view.

Slashdot has been a website for ten years.  It has lots of things to talk about.  Some of the things are: computers, the Internet, video games, and politics.

Many people like Slashdot because you can share ideas.  People who like computers and the Internet can read the ideas to learn.

Anyone can go to Slashdot and read it and do not need to give money.  People from every country go.  It has many ideas which are never the same.

Other websites 
http://slashdot.org/

Websites
It is a law of mechanics and physics discovered by Robert Hooke. 

This theory of elasticity says the extension of a spring is proportional to the load applied to it. Many materials obey this law as long as the load does not exceed the material's elastic limit. Materials for which Hooke's law is useful are known as linear-elastic or "Hookean" materials.

The spring equation 
The length of a spring always changes by the same amount when it is pushed or pulled. The equation for this is:

where
F is how much (push or pull) is on the spring 
k is a constant, the stiffness of the spring. 
 x is how far the spring was pushed or pulled 

When x = 0, the spring is at the equilibrium position. 
This equation only works on a linear spring. A linear spring is a spring that is only being pushed or pulled in one direction, such as left or right or up or down.

Elastic potential energy 
Examples of everyday objects that have elastic potential energy are stretched or compressed elastic bands, springs, bungee cords, car shock absorbers, etc. 

Elastic potential energy is the energy saved in an object that is stretched, compressed (compression is pressing objects together), twisted or bent. For example, an arrow gets the elastic potential energy from the bow. When it leaves the bow, the potential energy turns into kinetic energy. 
The equation of the elastic potential energy is:

Which means:
U is the elastic potential energy.
k is the spring constant. 
 x is the distance pushed or pulled.

Mechanics
Time is an American news magazine. It was founded in 1923. It is printed every week in the United States. It is published by Time Inc. It has articles on politics and current events. It is read by more people than any other news magazine.

There is also a magazine called Time For Kids, aimed at children. That magazine is eight pages long and contains more images and shorter articles than the regular Time magazine.

1923 establishments in the United States
American magazines
Weekly magazines
Time Warner
Magazines published in New York City
An antenna or aerial is a metal device made to send or receive radio waves. Many electronic devices like radio, television, radar, wireless LAN, cell phone, and GPS need antennas to do their job. Antennas work both in air and outer space. 

The word 'antenna' is from Guglielmo Marconi's test with wireless equipment in 1895. For the test, he used a 2.5 meter long pole antenna with a tent pole called ' l'antenna centrale ' in Italian. So his antenna was simply called ' l'antenna '.  After that, the word 'antenna' became popular among people and had the meaning it has today. The plural of antenna is either antennas or antennae (U.S. and Canada tends to use antennas more than other places).

Types of antennas 
Each one is made to work for a specific frequency range. The antenna's length or size usually depends on the wavelength (1/frequency) it uses.

Different kinds of antenna have different purposes. For example, the isotropic radiator is an imaginary antenna that sends signals equally in all directions. The dipole antenna is simply two wires with one end of each wire connected to the radio and the other end standing free in space. It sends or receives signals in all directions except where the wires are pointing. Some antennas are more directional. Horn is used where high gain is needed, the wavelength is short. Satellite television and radio telescopes mostly use dish antennas.

References

Radio antennas
John Griffith "Jack" London (born John Griffith Chaney, January 12, 1876 – November 22, 1916) was an American writer. He wrote many books. He lived in the U.S. state of California but also spent a lot of time in Hawaii and Alaska.

His most famous book was The Call of the Wild.  The Call of the Wild is about a dog named Buck who is taken to Alaska to work with a pack of dogs pulling a sled.  This book took place during the Klondike Gold Rush. Many people bought The Call of the Wild and Jack London became a famous writer. He also wrote other books about dogs and wolves. Another one of his famous books is White Fang.

Jack London was also a hobo at one time.  He wrote a book about this called The Road. Jack London had political beliefs.  He was a socialist.  One of his famous books is The Iron Heel, which is the story of the government using force against the socialist movement.

He also spent some time at sea and making a living as an "oyster pirate".  He wrote many books about sailing and boats.  One of his best-known books about life at sea was The Sea Wolf.

He married Charmian London born Kittredge (second wife). She was an athletic woman and an intellectual companion that broke the mold of Victorian womanhood—though they grew apart when she turned to socialite circles. His feminism was matched by models of sensitive "virility" and he sorted out the master-slave model of government in order to find alternatives.[3] He was on the vanguard of animal welfare and attempted a model pig farm, and experimented with early ecological agriculture, but Wolf House (his dream home) burnt to the ground in what could have been arson.[4] He died in a state of depression.

References

 Reesman 2009, p. 23.
3. Cf. Saiz, Peter Ralph, "Political Tyranny and the Master-Slave Paradigm in Selected Sea-Tales of Herman Melville and Jack London", PhD thesis Purdue University 2003. https://docs.lib.purdue.edu/dissertations/AAI3113867/ Cf. also, Huebert, David, "Species Panic: Interspecies Erotics in Post-1900 American literature", PhD thesis University of Western Ontario 2018. 4. Cf. http://santarosahistory.com/wordpress/2016/11/the-case-for-arson-at-wolf-house/. Cf.Fresneau-Woodward, Servanne, "Nature animale et paysages naturels dans l'oeuvre de Jack London" Doctorat, Université de Paris X https://www.theses.fr/1987PA100174

American novelists
Writers from San Francisco
Writers from Alaska
Writers from Hawaii
1876 births
1916 deaths
Jerk is the change in the acceleration of an object. Mathematically, jerk is the derivative, or the rate of change of acceleration by time. Jerk is also called jolt (in British English), surge, or lurch. Jerk is a vector and there is no word for its scalar value. 

The jerk is measured in metres per second cubed ().

Yank can be thought as a force in terms of jerk. Force is mass times acceleration. Similarly, Yank is mass times jerk. It is also the derivative of the force. However, when an object is moving near the speed of light, a force is often written as the derivative of momentum. In this case, Yank is the rate of change of the derivative of momentum.

Its use 
Jerk is used in engineering, particularly in making roller coasters. Weak objects such as people can be damaged by high acceleration or high jerk.
Also, jerk must be thought in the process of making any product. Sudden change in acceleration means very large jerk. Extent of exposure to jerk is often a good predictor of the rate of deterioration of tools while in normal use; it corresponds better to the appearance of metal fatigue among other modes of failure.

Mechanics
physical quantity
An electric current is a flow of electric charge. The equation of current is:

where
 is the current flowing
 is the change in electric charge
 is the change in time

The SI unit of electric current is the ampere (A). This is equal to one coulomb of charge in one second.
Current can be found in wires, batteries, and lightning.

The source of current 
In conducting materials, some electrons are very loosely bound to the atoms of the material.  When large amounts of these atoms come together, there is a sort of electron cloud that "hovers" near the atoms of the material.  If you examine a cross-section of the piece of conducting material, the electrons will move very quickly through it.  This motion is caused by temperature, and electrons flowing in one direction tend to equal the electrons flowing from the other direction, so this is not what causes current to flow.  Electrons flow from one atom to another, a process has been compared to the passing of water buckets from one person to another in a bucket brigade.

When an electric field is put on the wire, the electrons respond almost instantly by drifting slightly in the opposite direction of the field.  They gain energy from the field, which is lost very quickly when they bump into other electrons in the material.  As long as the field is in place, however, the electrons will gain back that energy that they lost, and the process will continue.  This "jolt" that electrons receive from the electric field is the source of current, not the overall flow of electrons themselves.  From this discussion, we can see two things that current is not:

It is not an actual "flow" of electrons in the everyday sense of the word:  If we examine the speed given to the electrons by the field, it is usually very small, on the order of millimeters per second.  It would take half an hour for electrons to cross a 10-foot (3 m) room at this rate.  Since a light bulb flips on almost immediately after hitting the switch, something else must be at work.
It is also not a "domino effect", although this analogy is closer than the flow.  Since electrons are so tiny, even when they are moving very quickly they are not being propelled by great force.

Current in circuits 
When current is flowing in a wire circuit, it accelerates when there is no resistance in the circuit. Resistors are used to increase resistance in the circuit so it slows down the current. The relationship between resistance, current, and voltage (another part of the circuit) is shown by Ohm's law.

References 

Electricity
Inbreeding is a term in genetics, meaning the crossing (mating) of closely related animals or plants.  Self-fertilisation in plants is the most extreme kind of inbreeding.  It is quite widespread in plants which carry both male and female flowers on the same plant. Inbreeding is the opposite of outcrossing, which is the mating of unrelated members of the same species. The combination of inbreeding and outcrossing is a standard method of artificial selection.

Other terms are inbred strain, a group of organisms so inbred that they have little or no genetic variation, and inbreeding depression, which is the decreased fitness (usually lack of fertility and early illness and death) brought about by inbreeding.

For human beings, inbreeding is destructive, and almost all cultures have an incest taboo. For example, many prohibit marriage between first cousins, and most prohibit it for closer family members.

Loss of genetic variation 
Loss of genetic variation means that many gene loci that were heterozygous are now homozygous. The result of both genes at a locus being mutant can be serious. 

The most intense form of inbreeding is the self-fertilisation in an hermaphrodite, in which the proportion of heterozygotes is halved in each generation.p139 Aa x Aa (100%) gives 1 AA: 2 Aa; 1 aa (50%), and so on. A similar effect takes twice as long with brother-sister mating, and longer still with mating in very small isolated groups. The latter situation is famous because Sewall Wright did his calculations for just such groups, and he called the process genetic drift. Genetic drift and inbreeding are closely related concepts.

The degree of inbreeding can be measured in various ways. A simple test for mammals is the exchange of skin grafts. If the grafts are not rejected, the animals must be nearly identical genetically. Skin grafts can be successfully exchanged between rats in standard laboratory strains, and between cheetahs caught in the wild.

Discussion 
Why is it that inbreeding brings about a loss of viability? There are two answers, and both seem to be true. The first is that a group with little genetic variation is vulnerable to environmental challenges: infections, sudden climate events, predators. Small groups are vulnerable to chance events in any case, but with no heritable variability they are even more vulnerable.

The second explanation is genetic. Some of the homozygous genes will be deleterious recessives which would normally be shielded by a dominant allele. Also, there are some loci where the heterozygote is inherently fitter than either homozygote. If so, inbreeding will automatically cause a loss of vigour.p103

Many plant species do self-pollination in the wild, but the great majority have occasional outcrossing. This provides them with sufficient variety for their survival.

Related pages
 Breed

References 

Classical genetics