Aarushhh/wikipedia-simple-splitted huggingface dataset:
He also had problems with the atomic theory. He did not believe in Democritus' theories about the atomic theory. He believed that all matter was continuous whereas Democritus stated the all matter was made up of tiny indivisible things called "atoms". Democritus was proved right by physicist John Dalton in 1804.

Logic 
Aristotle created a form of logic. His logic is called sentential logic because it uses sentences for the syllogism.

Aristotle's logic influenced the history of Western thought. It was his logic which was copied and used in the Arabic and Latin mediaeval traditions. It was dominant for two and a half thousand years, until the late 19th century. Then modern logic was started by Gottlob Frege, Charles Sanders Peirce and others.

Biology
Biology 

Aristotle is the earliest natural historian whose work has survived in some detail. He certainly did research on the natural history of Lesbos, and the surrounding seas and neighbouring areas. The works History of Animals, Generation of Animals and Parts of Animals have observations and interpretations, along with some myths and mistakes.

The most striking passages are about the sea-life round Lesbos. As well as live observation, he got specimens from the catches of fishermen. His observations on catfish, electric fish (Torpedo) and angler-fish are detailed. His writing on cephalopods such as Octopus, Sepia (cuttlefish) and the paper nautilus (Argonauta argo) are accurate. His description of the hectocotyl arm, used in sexual reproduction, was widely disbelieved until its rediscovery in the 19th century. He separated the aquatic mammals from fish, and knew that sharks and rays were part of the group he called Selachē (Selachimorpha).
Another good example of his methods comes from the Generation of Animals in which Aristotle describes breaking open fertilized chicken eggs at intervals to observe when visible organs were generated.

He gave accurate descriptions of ruminants' four-chambered fore-stomachs, and of the ovoviviparous egg development of the houndshark Mustelus mustelus.
The works 
The works are traditionally listed in this sequence:
 Logic
 Categories (terms)
 On Interpretation (propositions, truth)
 Prior Analytics (syllogistic logic)
 Posterior Analytics (scientific method)
 Topics (rules for argument and debate)
 On Sophistical Refutations (fallacies)
 Science and nature
 Physics (change, motion, void, time)
 On the Heavens (not the religious concept: refers to astronomy)
 On Generation and Corruption (on the process of life)
 Meteorology (origin of comets, weather, disasters)
 The Parva Naturalia (psychological works)
 Sense and sensibilia (faculties, senses, mind, imagination)
 On Memory,
 Sleep, Dreams, and Prophesy
 Length of life
 Works on natural history
 History of Animals
 On the parts of Animals
 On the Movement of Animals
 On the Progression of Animals
 On the Generation of Animals
 Problems
 Philosophical works
 Metaphysics (substance, cause, form, potentiality)
 Nicomachean Ethics (soul, happiness, virtue, friendship)
 Eudemian Ethics, virtues & vices
Politics (best states, utopias)
 Rhetoric (debate)
 Poetics (tragedy, epic poetry)
 The Constitution of the Athenians
 Fragments
Influence of Aristotle's work 
Aristotle is still one of the most influential people who ever lived. He contributed to almost every kind of knowledge in his day, and he started many new fields. 
"It is doubtful whether any human being has ever known as much as he did".

Aristotle was the founder of formal logic, pioneered the study of zoology, and helped to develop scientific method.

Despite these achievements, Aristotle's errors are thought by some, such as Peter Medawar, to have held back science considerably. Bertrand Russell notes that "almost every serious intellectual advance has had to begin with an attack on some Aristotelian doctrine". Russell also refers to Aristotle's Ethics as "repulsive", and calls his logic "as definitely antiquated as Ptolemaic astronomy". Russell says these errors make it difficult to do historical justice to Aristotle, until one remembers what an advance he made on his predecessors.
The immediate influence of Aristotle's work was felt as the Lyceum grew into the Peripatetic school of philosophers. Aristotle's influence over Alexander the Great is seen in the latter's bringing with him, on his expedition, biologists and researchers.

Related pages
List of biologists

References

Other websites 

 Works by Aristotle

384 BC births
322 BC deaths
Ancient Greek philosophers
Ancient Greek writers
Polymaths
Carl Edward Sagan (November 9, 1934 - December 20, 1996) was an American astronomer. He was very interested in what life on other planets would be like, which is known as SETI (search for extraterrestrial intelligence).

Sagan was a science communicator, which meant he taught people about science. He felt like the general public was losing interest in science, so he wrote many books and appeared on television to make it popular again. He mostly talked about planetary science and topics related to space. One of his most famous works includes. Cosmos: A Personal Voyage. Cosmos was a television series about many different scientific topics, which Sagan co-wrote and narrated. It made him very famous outside the world of science.

Sagan supported the scientific method and scientific skepticism.

Education and work
Carl Sagan was born in Brooklyn, New York City. Carl's family was Jewish. His father, Samuel Sagan, was an immigrant from the Russian Empire. Samuel was born in 1905 in a city called Kamianets-Podilskyi. The Russian Empire no longer exists, so today Kamianets-Podilskyi is in Ukraine. Samuel made clothes for a living. Carl's mother, Rachel Molly Gruber, was a housewife. Carl had a sister named Carol, who became a social worker. Carl was named after his grandmother, Chaiya (Clara).

Sagan attended the University of Chicago earning two degrees in physics. He followed with a doctorate in astronomy in 1960 and taught at Harvard University until 1968, when he moved to Cornell University.
Sagan became a teacher and director at Cornell in 1971. He helped many unmanned spacecraft to explore outer space. He thought of the idea of putting a message on spacecraft which could be understood by any life from another planet that might find it. The first message sent into space was a large gold-plated label on the space probe Pioneer 10. He continued to make the messages better. The last message he helped with was the Voyager Golden Record that was sent out with the Voyager space probes.

Scientific achievements 

He was well known as a writer who warned of the dangers of nuclear winter. He helped people learn about the atmosphere of Venus, seasonal changes on Mars, and Saturn's moon Titan. He showed that the atmosphere of Venus is very hot and dense. He also said that global warming was a growing, man-made danger like the natural development of Venus into a hot and dangerous planet with greenhouse gases. He suggested that the seasonal changes on Mars were due to dust storms.
Sagan was among the first to guess that Titan and Jupiter's moon Europa might have oceans or lakes, which means that life could be there. Europa's underground ocean was later confirmed by the spacecraft Galileo.

Sagan thought the search for life on other planets was a good idea. He said scientists should listen with large radio telescopes for signals from other planets. He thought sending probes to other planets was a good idea. Sagan was editor Icarus (a magazine about space exploration) for 12 years. He helped start the Planetary Society and was a member of the SETI Institute Board of Trustees.

Social concerns 

Sagan also believed that the Drake equation suggested that many kinds of intelligent life could form, but that the lack of evidence (the Fermi paradox) suggests that intelligent beings destroy themselves rather quickly. This made him keen to talk about ways that humanity could destroy itself, in the hope of avoiding such destruction.
Under the name "Mr. X," Sagan wrote about pot smoking in the 1971 book Reconsidering Marijuana. Lester Grinspoon (the book's editor), told this to Keay Davidson, Sagan's biographer. Sagan said that marijuana helped him write some of his books.

Making science popular 

Sagan was very good at helping people to understand the cosmos. He gave the 1977/1978 Christmas Lectures for Young People at the Royal Institution. He wrote (with Ann Druyan, who became his third wife) and made the very popular thirteen-part PBS television series Cosmos; he also wrote books to help science become more popular (The Dragons of Eden, which won a Pulitzer Prize, Broca's Brain, etc.) and a novel, Contact, that was a best-seller and was made into a film starring Jodie Foster in 1997. The film won the 1998 Hugo Award.
After Cosmos, Sagan was linked with the catchphrase "billions and billions", which he never used in the television series (but he often used the word "billions"). He wrote Pale Blue Dot: A Vision of the Human Future in Space, which was chosen as a notable book of 1995 by The New York Times.

Not all scientists agreed with him. Although they all liked the way he made science popular, some were afraid that people would think that his personal opinions might be confused with real science. What he said about the Kuwait oil well fires during the first Gulf War were shown later to be wrong.
Later in his life, Sagan's books showed his skeptical, naturalistic view of the world. In his book The Demon-Haunted World, Sagan gave a list of mistakes he had made as an example of how science is self-correcting. The compilation Billions and Billions: Thoughts on Life and Death at the End of the Millennium, published after Sagan's death, contains essays written by Sagan, such as his views on abortion, and Ann Druyan's account of his death as a non-believer.

Legacy 

After a long and difficult fight with myelodysplasia, Sagan died of pneumonia at the age of 62, on December 20, 1996, at the Fred Hutchinson Cancer Research Center in Seattle, Washington. Sagan was very important, because he made science popular, and changed the way science was organized, and because he defended humanism, and argued against seeing things from only one point of view.
The landing site of the unmanned Mars Pathfinder spacecraft was renamed the Carl Sagan Memorial Station in honor of Dr. Sagan on July 5, 1997. Asteroid 2709 Sagan is also named in his honor.

The 1997 movie Contact (see above), based on Sagan's novel of the same name, and finished after his death, ends with the dedication "For Carl."

Awards and medals
Apollo Achievement Award - National Aeronautics and Space Administration
 Chicken Little Honorable Mention - 1991 - National Anxiety Center
 Distinguished Public Service - National Aeronautics and Space Administration
 Emmy - Outstanding individual achievement - 1981 - PBS series Cosmos
 Emmy - Outstanding Informational Series - 1981 - PBS series Cosmos
 Exceptional Scientific Achievement Medal - National Aeronautics and Space Administration
 Helen Caldicott Leadership Award - Women's Action for Nuclear Disarmament
 Homer Award - 1997 - Contact
 Hugo Award - 1998 - Contact
 Hugo Award - 1981 - Cosmos
 Hugo Award - 1997 - The Demon-Haunted World
 In Praise of Reason Award - 1987 - Committee for the Scientific Investigation of Claims of the Paranormal
 Isaac Asimov Award - 1994 - Committee for the Scientific Investigation of Claims of the Paranormal
 John F. Kennedy Astronautics Award - American Astronautical Society
 John W. Campbell Memorial Award - 1974 - The Cosmic Connection
Konstantin Tsiolkovsky Medal - Soviet Cosmonauts Federation
 Locus Poll Award 1986 - Contact
 Lowell Thomas Award - Explorers Club - 75th Anniversary
 Masursky Award - American Astronomical Society
 Peabody - 1980 - PBS series Cosmos
 Public Welfare Medal - 1994 - National Academy of Sciences
 Pulitzer Prize for Literature - 1978 - The Dragons of Eden
 SF Chronicle Award - 1998 - Contact
 Carl Sagan Memorial Award - Named in his honor
Sagan, Carl and Jonathon Norton Leonard and editors of Life, Planets. Time, Inc., 1966
 Sagan, Carl and I.S. Shklovskii, Intelligent Life in the Universe. Random House, 1966
 Sagan, Carl, Communicaton with Extraterrestrial Intelligence. MIT Press, 1973
 Sagan, Carl, et al. Mars and the Mind of Man. Harper & Row, 1973
 Sagan, Carl, Other Worlds. Bantam Books, 1975
 Sagan, Carl, et al. Murmurs of Earth: The Voyager Interstellar Record. Random House, 1977
 Sagan, Carl et al. The Nuclear Winter: The World After Nuclear War. Sidgwick & Jackson, 1985
 Sagan, Carl and James Randi, The Faith Healers. Prometheus Books, May 1989, , 318 pgs
 Sagan, Carl and Richard Turco, A Path Where No Man Thought: Nuclear Winter and the End of the Arms Race. Random House, 1990
 Sagan, Carl, The Dragons of Eden: Speculations on the Evolution of Human Intelligence. Ballantine Books, December 1989, , 288 pgs
 Sagan, Carl, Broca's Brain: Reflections on the Romance of Science. Ballantine Books, October 1993, , 416 pgs
Sagan, Carl and Ann Druyan, Shadows of Forgotten Ancestors: A Search for Who We Are. Ballantine Books, October 1993, , 528 pgs
 Sagan, Carl and Ann Druyan, Comet. Ballantine Books, February 1997, , 496 pgs
 Sagan, Carl, Contact. Doubleday Books, August 1997, , 352 pgs
 Sagan, Carl, Pale Blue Dot: A Vision of the Human Future in Space. Ballantine Books, September 1997, , 384 pgs
 Sagan, Carl and Ann Druyan, Billions & Billions: Thoughts on Life and Death at the Brink of the Millennium. Ballantine Books, June 1998, , 320 pgs
 Sagan, Carl, The Demon-Haunted World: Science As a Candle in the Dark. Ballantine Books, March 1997, , 480 pgs
 Sagan, Carl and Jerome Agel, Cosmic Connection: An Extraterrestrial Perspective. Cambridge University Press, January 15, 2000, , 301 pgs
 Sagan, Carl, Cosmos. Random House, May 7, 2002, , 384 pgs
 Zemeckis, Robert, Contact. Warner Studios, 1997, ASIN 0790736330 IMDB 
 Davidson, Keay, Carl Sagan: A Life. John Wiley & Sons, August 31, 2000, , 560 pgs
Other websites 

 In Memory of Carl Sagan. Tributes by Tom McDonough, James Randi and Michael Shermer, and a selection of quotes from Sagan's works, published in Skeptic, Vol. 4, no. 4, 1996, pp. 10–17.
 CarlSagan.Com. Homepage of Cosmos Studios, which sells the Cosmos series on DVD and VHS video tape.
 Carl Sagan, Cornell astronomer, dies today (Dec. 20) in Seattle. Cornell University press release on Sagan's death.
 Even in Death, Carl Sagan's Influence Is Still Cosmic by William J. Broad, The New York Times, November 30, 1998. Describes Sagan's legacy for space science.
 Astronomy Picture of the Day: Carl Sagan. December 26, 1996.
 Contact: A Eulogy to Carl Sagan, by Dr. Ray Bohlin, president of Probe Ministries. Dr. Bohlin suggests that the movie Contact can serve as a fitting eulogy for Carl Sagan. Sagan's scientific approach to the question, "was the universe created?" is critically analyzed by Bohlin from his Christian perspective.
 The Untold Truth about Carl Sagan Grunge.com

References
References

1934 births
1996 deaths
Agnostics
American astronomers
Deaths from pneumonia
Infectious disease deaths in the United States
Jewish American scientists
Jewish American writers
Pulitzer Prize winners
Scientists from New York (state)
Writers from New York City
Emmy Award winners
Matsuo Munefusa, known as Matsuo Bashō (, 1644 - November 28, 1694) was a Japanese poet. He is known as the greatest maker of haiku, a kind of poetry with 17 syllables. The Japanese written language was difficult to master, but haiku was easy for him to write. Matsuo's haikus included characteristics of nature and the four seasons. The reader has to use their imagination to understand his poems.

According to Japanese custom, he is usually called Basho without his family name, and his signature as a poet does not include his house name. He signed usually "はせを". He is one of the greatest writers of the Edo period, and he raised the haiku form to its highest level.
He was born in Iga, now a part of Mie prefecture in a samurai (Japanese warrior) family. After many years of samurai life he found that poetry would be his life work, and gave up being a samurai. He started his life as a poet when he served his lord as a samurai. Matsuo became educated in classical Japanese poems. First he named himself Tosei (桃青) meaning "unripe peach in blue". Basho took this name because he admired a Chinese poet, Li Po whose name means plum in white.

He quit samurai life 1666, and in 1675 he moved to Edo, today called Tokyo. There, in 1678, he got to be a haiku master ("Sosho") and began the life of a working poet. In 1680, he moved to Fukagawa, where he had a house. This was just outside of Edo. One of his followers gifted him a banana plant (basho-an). He planted the plant and called himself Basho because it became his favorite tree in his garden.
In his life, Basho visited many places. Those travels were important for his writings. He visited his disciples (followers) and taught them by making renga, a series of haiku, with them. He also visited famous places in Japanese history. These visits made his writing much stronger.

His most famous book is Oku no Hosomichi ("The Narrow Road Through the Deep North"). This book was written after a trip. On the trip, Basho and his disciple left Edo on March 24, 1689. They went around Tohoku and Hokuriku, and returned to Edo in 1691. The trip in this book ends in Ogaki, Mino (Gifu prefecture today) with one of his haiku where he hinted that he wanted to visit Ise shrine after staying in Ogaki. Matsuo was considered to have written some of the most beautiful travel diaries ever written in Japanese.

Basho died because of disease in early autumn of 1694 in Osaka, while staying at a house of his disciple on a trip.  Before his death, he made a haiku as his last words:
Tabini yande / yume ha kareno wo / kake meguru
On travel I am sick
My dream is running around
a field covered with dried grass

Notes

1644 births
1694 deaths
Japanese poets
Colonization is the act of one country settling another place, in order to become the new rulers of the new country, and to live in the new country. An early example is the settlers who went from the cities of Ancient Greece to start new cities.

In 1492, Christopher Columbus landed in the Americas. This is how the Europeans learned that North America and South America were there.  The Europeans colonized the Americas. Because of this, and the killing of many Native Americans, most people now living in North America are the descendants of Europeans.

Sometimes, science fiction stories talk about space colonization on space stations or planets other than Earth. Some science fiction stories like The Matrix speak of the robots the human beings made, taking over, and colonizing Earth.

Related pages
Annexation
Colonialism
Colony
Decolonization
Protectorate

International relations
Colonialism
Choreography (dance-writing) is the art of making dances. It tells dancers how they should dance and move. The word has been used since the late 18th century to mean the art of composing dance.

A person who does choreography is called a choreographer. A choreographer makes a dance based on music or a synopsis (a writing of what occurs in the dance). They may also act as trainers for professional dancers in ballet, stage shows and competitive ballroom dance. Their ideas may be recorded in dance notation, or on videos.

Choreography is also used in other types of performances. In Ice skating and Ice dancing, the choreographer designs the moves the skates does. In theater, movies and television, a choreographer is used to design fight scenes. For example, Bob Anderson designed many of the sword fight scenes in the Lord of the Rings movies as well as some of the Star Wars movies. A person who does this type of choreography is usually called a fight choreographer.

References 

Dance
An electrical cell is a device used to generate electricity, or to make chemical reactions  by applying electricity. A battery is one or more cells, connected. This cell is also known as electrochemical cell.

Cells producing electricity 
The simple electrical cells were first developed in 1800s. They are also called galvanic cells, because an Italian scientist named Luigi Galvani invented these cells.

Special chemical reactions which occur inside the electrical cell, result in oxidation and reduction of the substances inside the cell. This produces electrical energy. Normal batteries work like this.

Some electrical cells produce electricity without using chemical energy. For example, solar cells produce electricity when they are exposed to sun light.
A plate of zinc and a plate of copper immersed in a dilute solution which contains acid or salt is an example of the chemical reaction based cell. The solution acts as an electrolyte (electric conductor). When the two plates are connected to a current meter with a wire, electric current will pass; this is because oxidation and reduction processes take place in this chemical reaction turning the zinc plate to a negative electrode and the copper plate to a positive electrode, and so the electrons flow from zinc to copper.

Cells using electricity 
Some chemical reactions need high energy to happen. An example is the breakdown of water into hydrogen and oxygen. An electrical cell (or an "electrolytic cell") is used for these reactions. It is a container which has to have a chemical reaction involving electrodes. The chemical substances are exposed to electrical power, and the electrolysis reaction happens inside the electrical cell.
Two pieces of metal are placed in water that has a little electrolyte such as hydrochloric acid, sulfuric acid, sodium bicarbonate, or sodium hydroxide added to it. An electric current is applied and gas comes out of each electrode. Some greenish-brown color may be seen too if iron was used. 

There may also be a chemical reaction which will result in the explosion of the iron and has a strong blast radius (safety goggles recommended).

Related pages
 Battery

References 

Tools
Electricity
Dry cells are a type of chemical cells. Dry cells are commonly used today in the form of batteries. Dry cells are used in many electrical appliances. Most dry cells are not truly dry; they still contain a liquid electrolyte, but it is immobilized in a paste or gel. Several truly dry, or solid-state, batteries have been developed, but none are commercially available yet.

Types of dry cells
Primary cells
Zinc-carbon cells, also known as Leclanche cells
Alkaline cells
Lithium cells
Mercury cells
Silver oxide cell
Secondary cells
Nickel-cadmium cell
Lithium-ion cell
Nickel metal-hydride cell
Sealed lead acid battery

Primary cells are not rechargeable. They have to be thrown away after their chemicals are used.

Secondary cells are rechargeable. They can be used again.

Related pages
Battery
Rechargeable battery
Table of batteries

References

Electronics
Physical chemistry
Batteries
The Vietnam War (also known as Second Indochina War, Vietnamese-American War or American War in Vietnam) lasted from 1 November 1955 to 30 April 1975. It was fought between North Vietnam and South Vietnam. North Vietnam was supported by the Soviet Union, China, and North Korea, and South Vietnam was set up by the United States and supported by South Korea, Thailand, Australia, New Zealand, and the Philippines. People from other countries also went to fight but not in their own national armies. The conflict between communist and capitalist countries was part of the Cold War.

The Viet Cong, also known as the National Liberation Front or NLF, was a South Vietnamese communist force that was helped by North Vietnam. It fought a guerrilla war against South Vietnamese anticommunist forces. The People's Army of Vietnam (also known as the North Vietnamese Army) engaged in a more conventional war by at times putting large forces to battle.
The Vietnam War was very controversial, especially in the United States. It was the first war to feature live television coverage and the first major armed conflict that the United States lost. The war became so unpopular in the United States that President Richard Nixon eventually agreed to send American soldiers home in 1973.

Background and causes 

France began to colonize Vietnam between 1859 and 1862, when it took control of Saigon. By 1864, it had controlled all of Cochinchina, in the south of Vietnam. France took control of Annam, the large central part of Vietnam, in 1874. After France defeated China during the Sino-French War (1884–1885), it took over Tonkin, the north of Vietnam. French Indochina was formed in October 1887 from these three areas of Vietnam (Cochinchina, Annam and Tonkin), as well as Cambodia. Laos was added after a war against Thailand, the Franco-Siamese War, in 1893.
During World War II, after Nazi Germany had defeated France in 1940, French Indochina was controlled by the Vichy French government, a puppet government recognized by Germany. In March 1945, the Japanese Empire launched the Second French Indochina Campaign. Japan occupied Indochina but surrendered in August 1945.

After the defeat of Nazi Germany, the Vichy government was no longer in control of France or its territories. The newly formed Provisional Government of the French Republic attempted to take back control of its former colonies in Indochina by force, if necessary, but France's efforts at regaining its colony in Vietnam were opposed by a communist Vietnamese army, the Viet Minh. 

The Viet Minh had been founded in 1941 by the Vietnamese Communist Party and was led by Hồ Chí Minh. That led to the First Indochina War between France and the Viet Minh. Fighting started with the French bombardment of Haiphong Harbor in November 1946 and ended with a triumph of the Viet Minh at Dien Bien Phu.
The United States began to send military advisors to help train and support the South Vietnamese Army. It was fighting against the Viet Cong, also known as the National Liberation Front, a communist party based in South Vietnam that was controlled with North Vietnam. The Viet Cong began a campaign of assassination in 1957. In 1959, North Vietnam dramatically increased its military assistance to the Viet Cong, which then began attacking South Vietnamese military units. Because of domino theory, the US feared that if communism took hold in Vietnam, it would then spread to other countries nearby.

Gulf of Tonkin Resolution
On 2 August 1964, the destroyer USS Maddox was in the Gulf of Tonkin, on an intelligence mission along North Vietnam's coast. The US said that three North Vietnamese torpedo boats attacked the destroyer. The Maddox fired back and damaged the three torpedo boats. The US later claimed that two days later, the torpedo boats again attacked the Maddox and the destroyer USS Turner Joy. In the second attack, the US ships did not actually see the torpedo boats, but it was said that they had been found by using the ship's radar.

After the alleged second attack, the US launched air strikes against North Vietnam. The Congress passed the Gulf of Tonkin Joint Resolution (H.J. RES 1145) on 7 August 1964 and so gave the president the power to run large-scale military operations in Southeast Asia without declaring war. There was little to no proof of the attacks, and it was believed by some that they had been an excuse for expanded US involvement in Indochina.
The communists were supplied by a vast network of hidden trails, known as the Ho Chi Minh Trail. It was very well hidden although many attempts were made by the US to bomb and destroy it. Supplies and soldiers from North Vietnam were sent through Laos to communists forces in South Vietnam. American planes heavily bombed the Ho Chi Minh Trail, and  of bombs were dropped on Laos. That slowed down but did not stop the trail system.

Severe communist losses during the 1968 Tet Offensive made it possible for the US to withdraw many soldiers. As part of a policy called "Vietnamization," South Vietnamese troops were trained and equipped to replace the Americans who had left. By 1973, 95% of the American troops had left.

All of the parties signed a peace treaty in Paris in January 1973, but the fighting continued until 1975, when the South Vietnamese government surrendered after its capital, Saigon, had fallen.

Guerrilla warfare
Guerrilla warfare

There were some large-scale battles during the Vietnam War, but most of the fighting was guerilla warfare, which is different from the large-scale battles fought between armies like those during World War II. 
In guerilla warfare, small units fight limited battles against an enemy force, set up ambushes, make surprise attacks, and then retreat to the countryside or blend into the local population. That also includes making it difficult for the enemy to operate by engaging in sabotage and harassing the enemy with lethal means such as the land mine and the booby trap. The communist troops more often engaged in guerilla warfare against South Vietnamese and American troops than the reverse because the communists knew of their weakness in conventional (large-scale) warfare.
Although few of the traps were explosive, all of the explosive traps used grenades. A tripwire was placed, and if a soldier tripped over the wire, a grenade pin was pulled out, the grenade would blow, and the soldier would usually be killed.

Another style of trap was nicknamed the Venus flytrap. It had about eight barbs attached to a rectangular frame sitting on a small hole. The barbs faced down so that when the soldier’s leg got caught in it, it would not hurt until he pulled his leg out, when the barbs would rip through his leg.

Another Viet Cong trap was the Punji trap. Two wooden platforms were placed and covered with leaves to camouflage it. There were spikes on the inside of the wood. When a soldier came along and walked on the wood, it caved in, and the spikes would go through the soldier’s foot. That trap was the most common because it was the cheapest one and was very effective. It was also often contaminated, often with feces, so that the soldier would also become infected.
Besides hurting or killing people, the traps caused fear and lowered morale.

Fall of Saigon

The Fall of Saigon was the capture of Saigon, the capital of South Vietnam, by the People's Army of Vietnam and the National Liberation Front on April 30, 1975. That marked the end of the Vietnam War and the beginning of the formal reunification of Vietnam into a communist state.

Before the city fell, the few American civilian and military personnel had left Vietnam, and tens of thousands of South Vietnamese soldiers and civilians had also fled.

The North Vietnamese forces, commanded by General Văn Tiến Dũng and began their final attack on Saigon, whose defence was commanded by General Nguyen Van Toan on April 29. A heavy artillery bombardment of Tân Sơn Nhứt Airport killed the last two American servicemen who died in Vietnam: Charles McMahon and Darwin Judge.
By the afternoon of the next day, North Vietnamese troops had occupied the important points within the city and raised their flag over the South Vietnamese presidential palace. The government of South Vietnam soon formally surrendered.

The Americans still in Saigon were evacuated by helicopter or fixed-wing aircraft. The surrender of Saigon was given in person by South Vietnamese President General Duong Van Minh: "We are here to hand over to you the power in order to avoid bloodshed." He was president for two days as his country crumbled.

Saigon was renamed Ho Chi Minh City after the communist leader Ho Chi Minh.

Aftermath 
The war made potential farmland useless, as it was bombed and affected by Agent Orange. The economy crashed because inflation was high and so unemployment was common, and there was poor health care. Many people fled Vietnam because of these conditions.
The Đổi Mới reforms helped to improve many of the problems that had been caused by the war. Although there are still many situations with serious economic issues, Vietnam now has a fairly successful economy. The income and the standard of living of the average Vietnamese people have kept improving since the 1990s.

The war also had lasting effects on the US. It led to divisions in American society that are still seen today, and many Americans became more wary of their government. Many veterans came back with PTSD and were not treated well; people who opposed the war saw them as killers, and people who supported the war saw them as losers.

Related pages
First Indochina War
Weapons of the Vietnam War

References

Other websites

The herbicide Agent Orange has left a lasting legacy on Vietnam
The Sahel is a narrow belt of land in North Africa. It is a strip of land about 5500 kilometers long and 450 kilometres wide. It lies at the southern edge of the Sahara Desert 

The Sahel has a tropical semi-arid climate. It is between the dry desert land to the north and the forest areas to the south. The temperature is high throughout the year. There is little rainfall in the Sahel (between 100 and 150 mm and 600mm). It comes during summer months and may be unreliable. It may be very dry in some years, especially if a large area of low pressure, which brings rain, is not carried North over the Sahel by strong winds.

The Sahel is the Arabic word for 'edge' or 'shore'.
The Sahel is facing a big problem, desertification.
The distribution of rainfall in the Sahel region is uneven. The rainfall in the region has been below average since 1970. The Sahel is becoming drier on the whole. The problem of drought affects most of the countries in the Sahel. As a result, crops and animals die. There is no vegetation to protect the soil, which is then removed by flash floods and strong wind. This leads to soil erosion. Finally, the desert spreads towards the surrounding areas.

With better medical services, the birth rate increases and the death rate decreases in the Sahel. As a result, the population in the Sahel is growing. To meet the ever-increasing demand for firewood, a lot of trees have been cut down. More land has become barren. This is called deforestation.

Furthermore, people farm intensively in order to grow more crops, the soil becomes infertile with a lack of nutrients. If this process continues for a long time, no crops can be grown. This is called overcultivation.
People keep animals for food due to the lack of good soil, the animals will have to eat grass and etc. But as the animals eat the grass, they also dug up the soil. As people keep too many animals, the demand for grass is too great. Soil erosion is caused while the animals keep digging the soil up as they eat, and the wind and rain blow away the soil. This process is called overgrazing.

Modern solutions can be used to give a better agricultural result in the Sahel. We can try drip irrigation or hybrid. We should stop using excessive water and consider our actions, to save the Sahel and lake Chad before it is too late.

References 

Geography of Africa
Biomes
A chemical change (chemical reaction) is a change of materials into other materials with different properties.

Chemical changes occur when a substance combines with another to form a new substance, or,  chemical decomposition into two or more different substances. These processes are called chemical reactions.

Burning of wood is a chemical change as new substances which cannot be changed back (e.g. carbon dioxide) are formed. For example, if wood is burned in a fireplace, there is not wood anymore but ash. Other examples  include burning of a candle, rusting of iron, baking a cake, etc. Special details that describe how a chemical change takes place are called chemical properties.                 

Compare: physical change. The opposite of a chemical change is a physical change. Physical changes are a change in which no new substances are formed, and the substance which is changed is the same. For instance, if a stick of wood is broken, there is still a stick of wood; it is just broken.
More examples include changes of shape, changes of states, passing electricity through a copper wire, breaking of wood, shattering of glass, pouring of water, etc. Special details which do not change in a substance without new substances being formed are called physical properties.   

Chemical reactions
A physical change is a type of change in which the form of matter is altered but one substance is not transformed into another. The size or shape of matter may be changed, but no chemical reaction occurs.

All physical changes are reversible and their mass does not change. Some examples are changes of shape, changes of states, and passing electricity through a copper wire. Physical changes could be: melting, freezing, boiling/evaporating, condensing, deposition and sublimation.

Many physical changes also involve the rearrangement of atoms most noticeably in the formation of crystals. Many chemical changes are irreversible, and many physical changes are reversible, but reversibility is not a certain criterion for classification. Although chemical changes may be recognized by an indication such as odor, color change, or production of a gas, every one of these indicators can result from physical change.  
Chemistry
Physics
Ronald Wilson Reagan ( ; February 6, 1911June 5, 2004) was an American politician and actor who was the 40th president of the United States from 1981 to 1989. He previously was the 33rd governor of California from 1967 to 1975 and was president of the Screen Actors Guild from 1947 to 1952 and from 1959 until 1960.
In his first term, Reagan created "Reaganomics", which included economic deregulation and cuts in both taxes and government spending during a period of stagflation. He grew an arms race and moved Cold War policy away from détente with the Soviet Union. He also survived an assassination attempt, had a feud with public sector labor unions, expanded the war on drugs, and ordered the invasion of Grenada in 1983. In the 1984 presidential election, Reagan was re-elected over former vice president Walter Mondale in another landslide victory. Foreign policy took over Reagan's second term, including the 1986 bombing of Libya, the Iran–Iraq War, the secret sale of arms to Iran to fund the Contras, and a more calm approach in talks with Soviet leader Mikhail Gorbachev that led to the Intermediate-Range Nuclear Forces Treaty.
Reagan left the presidency in 1989 with the American economy having seen far less inflation, less unemployment, and the United States having entered its then-longest period of economic growth. At the same time, the federal debt had nearly increased three times since 1981 as a result of his cuts in taxes and increased military spending, despite cuts to domestic discretionary spending. Alzheimer's disease made Reagan's post-presidency difficult and his physical and mental capacities quickly got worse, which led to his death in 2004. His presidency is a part of the Reagan era, and he is considered an important conservative figure in the United States. Historians and scholars have ranked Reagan among the upper tier of American presidents although disliked by some democrats today. Nonetheless, He is often viewed favorably among the general public.

Early life
Early life 

Reagan was born to Jack and Nelle Reagan on February 6, 1911, in a small apartment building in Tampico, Illinois. He had an older brother named Neil. His father was a Roman Catholic of Irish descent. His mother was a Protestant of English and Scottish descent.

The family moved to different places in Illinois when Reagan was a child. They moved to Monmouth, Galesburg, and Chicago. His family finally settled in Dixon, Illinois. They lived in a small house in Dixon. His family was very poor. Reagan did not have much as a child. In high school, Reagan enjoyed acting. Reagan was athletic. He became a lifeguard and saved 77 lives.
Reagan graduated from Eureka College in 1932. He became a sports announcer at news radio station WHO. Reagan was also a broadcaster for the Chicago Cubs. He was good at recreating baseball games. He made them interesting. At this time, the radio station would get only the scores. In 1936, Reagan went to California with the Cubs. The Cubs were there to practice baseball. While he was in California, Reagan got a seven-year contract with Warner Brothers. He left his job as a radio announcer to start acting.

Acting career
Acting career

Ronald Reagan was in fifty-three movies. His first screen credit was the starring role in the 1937 movie Love Is on the Air. He then starred in many movies such as Dark Victory with Bette Davis and Humphrey Bogart. Before the movie Santa Fe Trail with Errol Flynn in 1940, he played the role of George "The Gipper" Gipp in the movie Knute Rockne, All American. From his role in the movie, he got the lifelong nickname "the Gipper". In 1941, experts voted him the fifth most popular star from the younger generation in Hollywood.

Reagan's favorite acting role was as a double amputee in 1942's Kings Row. In the movie, he says the line, "Where's the rest of me?" It was later used as the title of his 1965 autobiography. Many movie critics thought Kings Row to be his best movie. Even though the movie was popular, it received bad reviews by New York Times critic Bosley Crowther.
Although Reagan called Kings Row the movie that "made me a star", he was unable to keep up with his success. This was because he was ordered to active duty with the U.S. Army in San Francisco two months after the movie's release.

During World War II, Reagan was separated for four years from his movie career. He served in the First Motion Picture Unit. After the war, Reagan co-starred in movies such as The Voice of the Turtle, John Loves Mary, The Hasty Heart, Bedtime for Bonzo, Cattle Queen of Montana, Juke Girl, This Is the Army, The Winning Team, Tennessee's Partner, and Hellcats of the Navy, in which he worked with his wife, Nancy. Reagan's last movie was a 1964 movie The Killers. Throughout his movie career, his mother, Nelle, often answered much of his fan mail.

Reagan was also a spokesperson. He hosted the General Electric Theater since it was first shown in 1953. He was fired in 1962.

In 1957, Reagan won a Hollywood Citizenship Award, which was a special Golden Globe Award.
President of the Screen Actors Guild
Reagan was first elected to the board of directors of the Screen Actors Guild in 1941. After World War II, he quickly returned to Screen Actors Guild. Reagan became the 3rd vice-president of the Screen Actors Guild in 1946.

Reagan was nominated in a special election to become president of the Screen Actors Guild. Reagan was elected in 1947. Reagan was president of the Screens Actors Biold from 1947 to 1952. Reagan was re-elected president in 1959. He served only a year before resigning in 1960.

Reagan led the Screen Actors Guild during labor disputes, the Taft–Hartley Act, the House Un-American Activities Committee (HUAC) hearings and the Hollywood blacklist era.

FBI informant
During the late 1940s, Reagan and his then-wife Jane Wyman gave the FBI names of actors whom they believed were communists. Reagan even spoke at a special meeting at Congress on communism in Hollywood as well.
Although Reagan gave out names of actors who were suspected communists, he disagreed with the way people were using these names. Reagan said:
"Do they expect us to constitute ourselves as a little FBI of our own and determine just who is a Commie and who isn't?"

Entrance into politics 

Reagan was very active in politics near the end of his acting career. Reagan used to be a Democrat. He strongly supported the New Deal. He admired Franklin D. Roosevelt. Over time, Reagan became a conservative Republican. This was because he thought the federal government had too much power and authority. He made a famous speech against socialized medicine (government-run health care).

Reagan endorsed Dwight D. Eisenhower and Richard Nixon for the United States presidency. The last time Reagan supported a Democrat was when Helen Gahagan Douglas ran for the United States Senate.
Speech for Barry Goldwater 
During the 1964 presidential election, Reagan supported Republican candidate Barry Goldwater. He made a famous speech called "A Time for Choosing" to support Goldwater. In the speech he spoke against government programs and high taxes. Even though Goldwater did not win the election, Reagan gained popularity from it. In his speech, Reagan said,

"You and I have a rendezvous with destiny. We will preserve for our children this, the last best hope of man on earth, or we will sentence them to take the first step into a thousand years of darkness."

After Reagan gave this speech, many business people thought that Reagan could run for Governor of California.
Governor of California, 1967-75
After giving a speech for Barry Goldwater's presidential campaign in 1964, he was persuaded to run for governor. Reagan ran as a Republican against the then governor, Pat Brown during the 1966 gubernatorial election. Reagan won the election with 3,742,913 (57.55%) of the vote while Brown won 2,749,174 (42.27%) of the vote. Reagan was inaugurated on January 2, 1967.
During his years as Governor, Reagan stopped hiring government workers. He did this to slow the growth of California's workforce. Reagan also approved tax increases to balance the state budget. Reagan worked with the Democratic Party majority in the state legislature to help create a major reform of the welfare system in 1971. The reform helped give money to the poor and increase the pay of the rich. During his term as governor, Reagan served as the President of the Republican Governors Association from 1968 to 1969. In 1967, Reagan signed an act that did not allow the public carrying loaded guns. In 1968, a petition to force Reagan into a recall election failed.

Reagan ran briefly for president in 1968. He was not nominated by the Republican Party at the 1968 Republican National Convention as Richard Nixon was nominated.
On May 15, 1969, during the People's Park protests at the University of California, Berkeley, Reagan sent the California Highway Patrol and other officers to fight off the protests, in an event that became known as "Bloody Thursday". Reagan then called out 2,200 state National Guard troops to occupy the city of Berkeley for two weeks to crack down on the protesters.

Reagan ran for re-election in the 1970 gubernatorial election against assemblyman Jesse M. Unruh. Reagan won 3,439,174 (52.83%) of the vote while Unruh won 2,938,607 (45.14%) of the vote.

During his final term as governor, he played a major role in California's educational system. He raised student loans. This caused a massive protest between Reagan and the college students. Reagan would soon be criticized of his views of the educational system. 

Reagan left office on January 6, 1975, when Jerry Brown, Pat Brown's son, succeeded Reagan as governor.

1976 presidential campaign
In 1976, Reagan said he would run against President Gerald Ford to become the Republican Party's candidate for president. Reagan soon became the conservative candidate with the support of organizations such as the American Conservative Union, which became key supporters of his political run, while Ford was considered a more moderate Republican.

During his 1976 campaign, Reagan controversially used the pejorative phrase "welfare queen" to describe Linda Taylor who illegally misused her welfare benefits in 1974. He used Taylor and her criminal activities to defend his criticisms about social programs in the United States.

Reagan selected United States Senator Richard Schweiker of Pennsylvania as his running mate.

Reagan won a few primaries early such as North Carolina, Texas and California, but soon failed to win key primaries such as New Hampshire, Florida, and his native Illinois.
During the 1976 GOP convention, Ford won the nomination with 1,187 delegates to Reagan's 1,070. Ford would go on to lose the 1976 presidential election to the Democratic nominee, Jimmy Carter.

Though he lost the nomination, Reagan got 307 write-in votes in New Hampshire, 388 votes as an Independent on Wyoming's ballot, and a single electoral vote from general election from the state of Washington.

1980 presidential campaign