the-french-artist/wikipedia_20220301.simple_sentence_split huggingface dataset:
Some animals can see light polarization.
Finally, a photon has a property called spin.
Spin is related to light's circular polarization.
Photon interactions with matter
Light is often created or absorbed when an electron gains or loses energy.
This energy can be in the form of heat, kinetic energy, or other form.
For example, an incandescent light bulb uses heat.
The increase of energy can push an electron up one level in a shell called a "valence".
This makes it unstable, and like everything, it wants to be in the lowest energy state. (
If being in the lowest energy state is confusing, pick up a pencil and drop it.
Once on the ground, the pencil will be in a lower energy state).
When the electron drops back down to a lower energy state, it needs to release the energy that hit it, and it must obey the conservation of energy (energy can neither be created nor destroyed).
Electrons release this energy as photons, and at higher intensities, this photon can be seen as visible light.
Photons and the electromagnetic force
In particle physics, photons are responsible for electromagnetic force.
Electromagnetism is an idea that combines electricity with magnetism.
One common way that we experience electromagnetism in our daily lives is light, which is caused by electromagnetism.
Electromagnetism is also responsible for charge, which is the reason that you can not push your hand through a table.
Since photons are the force-carrying particle of electromagnetism, they are also gauge bosons.
Some matter–called dark matter–is not believed to be affected by electromagnetism.
This would mean that dark matter does not have a charge, and does not give off light.
A vector is a mathematical object that has a size, called the magnitude, and a direction.
It is often represented by boldface letters (such as , , ), or as a line segment from one point to another (as in ).
For example, a vector would be used to show the distance and direction something moved in.
When asking for directions, if one says "Walk one kilometer towards the North", that would be a vector, but if they say "Walk one kilometer", without showing a direction, then that would be a scalar.
We usually draw vectors as arrows.
The length of the arrow is proportional to the vector's magnitude.
The direction in which the arrow points to is the vector's direction.
Examples of vectors
John walks north 20 meters.
The direction "north" together with the distance "20 meters" is a vector.
An apple falls down at 10 meters per second.
The direction "down" combined with the speed "10 meters per second" is a vector.
This kind of vector is also called velocity.
Examples of scalars
The distance between two places is 10 kilometers.
This distance is not a vector because it does not contain a direction.
The number of fruit in a box is not a vector.
A person pointing is not a vector because there is only a direction.
There is no magnitude (the distance from the person's finger to a building, for example).
The length of an object.
A car drives at 100 kilometers per hour.
This does not describe a vector, as there is only a magnitude, but no direction.
More examples of vectors
Displacement is a vector.
Displacement is the distance that something moves in a certain direction.
A measure of distance alone is a scalar.
Force that includes direction is a vector.
Velocity is a vector, because it is a speed in a certain direction.
Acceleration is the rate of change of velocity.
An object is accelerating if it is changing speed or changing direction.
How to add vectors
Adding vectors on paper using the head to tail method
The Head to Tail method of adding vectors is useful for doing an estimate on paper of the result of adding two vectors.
To do it:
Each vector is drawn as an arrow with an amount of length behind it, where each unit of length on the paper represents a certain magnitude of the vector.
Draw the next vector, with the tail(end) of the second vector at the head(front) of the first vector.
Repeat for all further vectors: Draw the tail of the next vector at head of the previous one.
Draw a line from the tail of the first vector to the head of the last vector - that's the resultant(sum) of all the vectors.
Using component form
Using the component form to add two vectors literally means adding the components of the vectors to create a new vector.
For example, let a and b be two two-dimensional vectors.
These vectors can be written in terms of their components.
Suppose c is the sum of these two vectors, so that c = a + b. This means that .
How to multiply vectors
Using the dot product
The dot product is one method to multiply vectors.
It produces a scalar.
It uses component form:
Using the cross product
The cross product is another method to multiply vectors.
Unlike dot product, it produces a vector.
Using component form:
Here,  means the length of , and  is the unit vector at right angles to both  and .
Multiplying by a scalar
A soap bubble is a very thin film of soap water.
Their shape is a hollow, round ball, or sphere.
They have a colorful surface.
Soap bubbles do not last very long.
Sometimes they break in the air.
When they touch something else, they usually break.
When people talk about soap bubbles they think about them being pretty but short-lived.
So, they are a symbol for other things that are pretty but short-lived or unimportant.
Children enjoy playing with bubbles.
Sometimes, adults enjoy seeing art done with soap bubbles.
Tom Noddy, author of Bubble Magic,
Keith Michael Johnson,
Fan Yang,
Louis Pearl,
Reinhold Leppert,
Craig Glenday,
John Erck.
The Fire Brigades Union (FBU) is the main union for firefighters in the United Kingdom.
They make the group to improve pay and working conditions.
It was founded in 1918 in the London area as the Firemans Trade Union.
It soon grew to cover the entire country.
Today, it has around 50,000 members.
FBU homepage
Organisations based in London
A bicycle (or bike) is a small, human powered land vehicle with a seat, two wheels, two pedals, and a metal chain connected to cogs on the pedals and rear wheel.
A frame gives the bike strength, and the other parts are attached to the frame.
The name comes from these two words - the prefix "bi-" meaning two, and the suffix "-cycle" meaning wheel.
It is powered by a person riding on top, who pushes the pedals around with his or her feet.
Riding bicycles, which is also called cycling, is an important way to travel in several parts of the world.
The most popular type of cycling is Utility cycling.
It is also a common recreation, a good form of low-impact exercise, and a popular sport.
Road bicycle racing is the second most popular spectator sport in the world.
In 1817 a German professor, Baron Karl von Drais, created the first two-wheeled bicycle.
It was made of wood and had two wheels.
The front wheel could be turned using the handlebars in order to steer the bike.
However, it did not have pedals, so the rider would have to push their feet on the ground to make it move.
In the 1860s, French inventors added pedals to the front wheel.
However, it took a lot of effort to turn the pedals.
Later inventors made bikes out of metal only, and made the front wheel very big, giving higher speed.
This design was called the penny-farthing bicycle.
However, it was difficult to ride, since it could fall easily and the rider would fall far.
Several improvements were made in the 1880s and '90s.
In 1885, the safety bicycle was invented.
This had two wheels the same size so that the rider could sit at a lower height.
It was called the safety bicycle because it much easier to ride than the penny-farthing.
When stopping, the rider can simply put down a foot instead of completely dismounting.
Instead of pedaling and steering with the front wheel, the safety bicycle steers with the front wheel while the pedals turn the back wheel using a chain.
Brakes operated by hand levers on some bikes also increased safety.
In 1888, Scottish inventor John Boyd Dunlop re-invented a type of tire which was filled with air.
This made safety bicycles more comfortable.
Soon, the freewheel was invented.
This was a device inside the hub of the back wheel that allowed the wheel to spin even if the rider wasn't pedaling.
However, this meant the rider could no longer stop the bike by backpedaling.
As a result, better hand brakes were invented, and a different type of brake which could stop the bike if the pedals were turned backwards.
Later inventions included better brakes, and gears which made cycling over hills much easier.
During this time the bicycle became very popular.
Basic components common to most bikes include a seat, pedals, gearing, handlebar, wheels, and brakes, all mounted on a frame.
The majority also have a gear shifter.
The cyclist's feet push the pedals to make them go around in circles, which moves the chain, which turns the back wheel of the bike to make the bike move forwards.
The front wheel is connected to the handlebar, so turning the handlebar from side to side swivels the front wheel which steers the bike.
Types of Bicycles
The city bicycle is made for errands and commuting in cities.
It has a comfortable seat but is heavy.
It has front and back lights and a bell, and carriers for small cargoes.
It has mudguards to keep water and mud from spraying the rider.
The rider sits upright for comfort and easy steering in traffic.
"Bike share" systems usually provide " city-style bikes".
The mountain bicycle is used for riding on rough roads.
They have many speeds (usually more than 20), wide tires, and strong wheels.
The tire is specially designed to ride smoothly on hills, grass, and mountains.
The difference between a woman's bicycle and other bicycles is the location of the top tube.
When women began to ride bikes, they wore long skirts.
The manufacturers of bicycles changed the location of the top tube to make it easier for women to sit down on them while wearing a skirt.
Some utility bicycles are similar, for riders who make frequent stops.
The tandem bicycle is made for two people.
It has two pairs of pedals.
The cyclists sit one behind another.
The first cyclist steers the bicycle.
There are bicycles for three and more people.
There was a bicycle for 40 people.
Folding bicycles can easily be stored in a small place or carried a long distance on an airplane or other public transport.
Electric Bicycles have electric motors, usually inside the hub of either the front or rear wheel.
You can choose to ride using the motor only, or with pedals only or with both together.
In the U.S. the federal government has set a limit of 750 Watts and a top electric-powered speed of 20MPH to have only the rules that apply to bicycles and no extra restrictions such as operator license, vehicle license, registration or insurance requirements.
A road bicycle usually has narrow wheels, less than 1" (25 mm) wide, with a frame that is much lighter than a mountain bicycle.
Road bikes are efficient for longer distances.
Many have clips to attach your shoes, rather than just pedals.
There are variations, as some road bicycles have regular tires.
Road bicycle racing is a popular sport.
Recumbent bicycles come in several styles, but all of them have pedals in front of the seat, and the rider leans back while riding.
This is more comfortable for most people, but cost more.
Some types are lower to the ground, so it might be harder to see in traffic.
The fastest bikes in the world are recumbents.
Many thousands of people are hurt every year in bicycle accidents, and hundreds die.
Careful riding helps prevent accidents.
When riding on streets, it is safest to ride on the same side of the street that cars drive (which would mean riding on the right side of the road in countries where people drive on the right side of the road, and riding on the left in countries where people drive on the left).
To avoid hitting people, riders must obey signs that say "no bicycling", even if it does not seem to make sense at the time.
Low light makes bicycle lighting important.
It may not be safe to ride when it is dark.
Riders wear reflective clothing to be safer in low light.
Wearing a helmet makes bicycle riding safer.
Wearing a helmet does not mean that somebody cannot be hurt if they crash their bicycle, but it makes being hurt less likely.
Some bicycles have bells or horns that the rider can use to warn other people that they are riding by them.
Many places have a bicycle path linking houses with shops, schools and stations.
These make bicycling safer, letting cyclists stay away from busy motor traffic on dangerous roads.
Human-powered vehicles
A wheel is a disc or circle-shaped mechanical device.
Its main purpose is to allow things to roll; in other words, the wheel spins, and object on the wheels moves more easily along the ground.
It is a simple machine.
Most land vehicles roll on wheels.
Wheels are often used in pairs, connected by a rod of wood or metal known as an axle.
Many machines have wheels with teeth, known as gears.
The principle behind the wheel is that of mechanical advantage.
Wheel and axle
This is a machine in which the wheel and axle turn together.
It is the basis of many machines, not just vehicles.
The potter's wheel, the lathe and the windlass are examples.
Most experts believe that  the ancient Mesopotamians invented the wheel about 4000 BC.
People in Asia also discovered it on their own around 3500 BC.
The Inca and Maya had wheels on children's toys around 1500 BC, but they did not use wheels for work.
Africa south of the Sahara desert, Europe, and Australia did not have the wheel until people there met people from Europe.
Early wheels were solid disks; the spoked wheel was invented around 2000 BC.
The earliest documentation of a vehicle with wheels is a painting dated between 33503500 BC.
Things to do to get some practical experience and skill in some activity.
Repeatedly moving the human body to make it stronger or better at doing something.
This is called physical exercise.
Basic modes of physical exercises
People do physical exercises as a part of their healthy lifestyle to get stronger and healthier or stay strong and healthy or to improve their body image.
There are three basic modes of physical exercises:
Flexibility exercises help the human body in general or its part in particular to be able to reach farther and bend better.
Aerobic exercises help the body work hard for a long time.
Anaerobic exercises, like lifting weights, make the arms and legs stronger.
Exercise can be fun, but it is important for the exerciser to do what he likes and eat enough calories , so when he exercises he is building up muscles, not just breaking them down for fuel.
Carbohydrates are muscle-sparing; and if one does not get enough calories overall, there is the risk of burning muscles up with the fat to make up the deficit.
Exercise benefits
Benefits of exercise for all ages have been known since antiquity.
Marcus Cicero, around 65 BC, stated: “It is exercise alone that supports the spirits, and keeps the mind in vigor.”
The CDC recommends that adults should get 150 minutes of physical activity weekly.
Regular exercise has been shown to help high blood pressure, obesity, heart disease, diabetes, and depression, among others.
Exercise also helps people feel less tired.
Regular exercise can have a profoundly positive impact on depression, anxiety, and ADHD.
It also relieves stress, improves memory, helps sleep better, and boosts overall mood.
Studies show that exercise can treat mild to moderate depression as effectively as antidepressant medication but without the side-effects, of course.
Types of physical exercises
aerobics
bodybuilding
weight training
Percent means out of one hundred.
It is often shown with the symbol "%".
It is used even if there are not a hundred items.
The number is then scaled so it can be compared to one hundred.
Percent is also used to indicate changes in numerical quantities.
For example, we have a bowl of fruit with three apples and one orange.
The percentage of apples is 3 out of 4, or 3/4 = 75/100 = 75%.
A percentage is only one way of writing a ratio; one can also write it as a fraction or decimal.
There are ways to convert fractions to percentages or decimals to percentages.
Percentages are useful in practice, because it allows one to compare things that are not out of the same number.
For example, exam marks are often percentages, which can compare them even if there are more questions on one exam paper than the other.
Writing is the act of recording language on a visual medium using a set of symbols.
The symbols must be known to others, so that the text may be read.
A text may also use other visual systems, such as illustrations and decorations.
These are not called writing, but may help the message work.
Usually, all educated people in a country use the same writing system to record the same language.
To be able to read and write is to be literate.
Writing differs from speech because the readers need not be present at the time.
We can read writing from long ago, and from different parts of the world.
Text stores and communicates knowledge.
Writing is one of the greatest inventions of the human species.
It was invented after people settled in towns, and after agriculture started.
Writing dates from about 3,300BC, which is over 5000 years ago, in the Middle East.
Writing today is usually on paper, though there are ways to print on almost any surface.
Television and movie screens can also display writing, and so can computer screens.
Many writing materials were invented, long before paper.
Clay, papyrus, wood, slate and parchment (prepared animal skins) have all been used.
The Romans wrote on waxed tablets with a pointed stylus; this was popular for temporary notes and messages.
The later invention of paper by the Chinese was a big step forward.
Writing is traditionally done using a hand tool such as a pencil, a pen, or a brush.
More and more, however, text is created by input on a computer keyboard.
Definition of writing
Partial writing: Writing is any system of graphic symbols which conveys some thought.
Full writing: Writing is any graphic system which can convey any and all thought.p5
Therefore, depending on an author's definition of writing, the term may be used in different ways.
With many early systems we do not know what they do convey.
The central idea is that a full writing system must be able to represent anything that might be said in spoken language.p7, 217 From this point of view the invention of the rebus is an essential step.
We can only be sure a sign system is full writing if we can translate the symbols into a modern language.
In the case of some ancient scripts we cannot do this.
History of writing
Writing was invented independently a number of times.
The Sumerian, the ancient Egyptian, the Chinese and the Mayan writings are separate in their invention.p85 All these writing systems started with pictographs, symbols that stood for things.
Then they developed a mixture of methods.
Our own alphabetic system  is different.
It is based on the sounds of spoken language.
All alphabets are modified versions of the first one, which originated with the Phoenicians and the Ancient Greeks.
The Sumerians lived in Mesopotamia, between the Tigris and Euphrates rivers.
5000 years ago this was a fertile region and is now mostly in Iraq.
The Sumerians developed a form of writing called cuneiform.
Triangular marks were pressed into soft clay tablets.
After the clay had dried in the sun the tablets were baked.
Then they were carried somewhere else for others to read.
We know that its first uses were for trade, accounting and administration.
The earliest signs were mostly pictorial, but soon they stood as symbols for objects, ideas and sounds.
This writing system was extremely successful, and outlasted the Sumerian empire.
It was then used by other civilisations in the Middle East, such as the Old
Akkadian, Babylonian, Assyrian, Elamite, Hittite, Old Persian and Ugaritic empires.
The last cuneiform inscription was dated as AD75.
Thus the system had lasted for more than 3000 years.p71 Each version of cuneiform had to be deciphered separately, because all the languages were different.
Documents (including stone objects) written in more than one language provided the clues.
This is the most famous of the old forms of writing, or scripts.
It was invented at roughly the same time as cuneiform, yet was quite different in style, and used different materials.
Egyptians ended up with three writing systems for the same language.
Hieroglyphic: the famous pictorial language on stone monuments.
Hieratic: a cursive  ('running') script used by the priests.
Demotic: a cursive script used by the people.
The writing tools used varied according to the material which was written on.
The two cursive scripts were written with reed pens and carbon inks onto papyrus.
If the material was cloth, then the writing was done by a brush.
Many examples survive.
The hieroglyphs were inscribed (carved) into stone (hammer & chisel) or painted onto stone surfaces.
Many survive, some with the original colours intact.
The key event in the decipherment of hieroglyphic writing was the discovery of the Rosetta Stone.
This is a granite slab with the same message written in hieroglyphic, demotic and in Greek.
Ancient Greek is well understood, and made possible the interpretation of the other two scripts.
Chinese is the language with the largest number of native speakers.
Its history dates back to about 1400BC.p183 The Chinese writing system is idio-syllabic, a mixed method using characters which may have one or more of these elements:
Pictographic: representing objects.
Visual logic: the number '3' is three horizontal strokes.
Complex logic: the sun is a box with a horizontal mid-stroke.
Rebus: "sounds like..." the character for wheat is also used for 'come' because the words are homophonous (sound alike).
Semantic-phonetic: combination of a character for meaning with another for sound (pronunciation).
Chinese has a huge number of characters: in the region of 50,000.p186 Because of this, printing methods were never really successful in China, despite their early invention.
In the 14th century Wang Tzhen had sixty thousand wood block characters cut, a huge investment in time and money.
He printed 100 copies of a local gazette, and was author of a treatise on agriculture and other technical works.
Even with printing machines from Europe in the 19th century, the process was hampered by the huge number of characters, which slowed the composition to a snail's pace.
China has eight regional languages that are mutually unintelligible, and many true dialects.
The system appears to work mainly because as many as 70% speak Mandarin.
Fluency in Chinese reading and writing is undoubtedly difficult to achieve, and this must act as a brake on the drive for literacy.
There have been a number of attempts to reform or simplify the system.
The most radical in Pinyin, which is a program to replace Chinese characters with an alphabetic system.
This was supported by Mao, but faltered after his death.
It seems that the idea of an alphabet–a script based entirely upon sound–arose only once, and has been copied and adapted to suit many different languages.
Although no alphabet fits its language perfectly, it is flexible enough to fit any language approximately.
It was a unique invention.p12
Our alphabet is called the Roman alphabet, as compared with the Cyrillic and other alphabets.
All of these come from the ancient Greek alphabet, which dates back to about 1100 to 800BC.p167 The Greek alphabet was probably developed from the Phoenician script, which appeared somewhat earlier, and had some similar letter-shapes.
The Phoenician language was a Semitic language, often called Canaanite.
The Semitic group of languages includes Arabic, Maltese, Hebrew and also Aramaic, the language spoken by Jesus.
We do not know much about how the alphabetic idea arose, but the Phoenicians, a trading people, came up with letters which were adapted by the early Greeks to produce their alphabet.
The one big difference is that the Phoenician script had no pure vowels.
Arabic script has vowels which may be shown by diacritics (small marks above or below the line).
The oldest Qu'ran manuscripts had no diacritics.
Israeli children today use texts with vowel 'dots' added, to about the third grade.p89
No ancient script, alphabetic or not, had pure vowels before the Greeks.
The Greek alphabet even has two vowels for 'e' and two for 'o', to distinguish between the long and short sounds.
It is fairly clear from this that careful thought went into both the Phoenician invention and the Greek adaptation.
However, no details survive of either process.
Semitic scripts apparently derive from Proto-Sinaitic, a script of which only 31 inscriptions (plus 17 doubtful) are known.
It is thought by some researchers that the original source of this script was the Egyptian hieratic script.
By the late Middle Kingdom (about 1900BC) hieratic had added some alphabetic signs for representing the consonants of foreign names.
Egyptian activity in Sinai was at its height at that time.
A similar idea had been suggested many years before.
Undeciphered scripts
There are a number of scripts which have never been deciphered, despite much effort.p145 Perhaps the most famous are the script of the Indus Valley civilization, and Etruscan.
The Indus River civilisation predates other literate civilisations on the Indian subcontinent, going back to about 2500BC.
Their cities of Mohenjo-Daru and Harappa were well-planned, with good drainage.
The script is found on seal stones, terracotta, bronze, bone and ivory.
All are brief, and the language is unknown.
The Etruscan language used Greek letter-forms, and is found mainly on Etruscan tombs, from Tuscany through to Venice.
They were an empire before the Romans, who defeated them, and absorbed their ideas.
All knowledge of their language was lost, except that some of the names on tomb memorials can be read from the Greek letters.
Vinča symbols
The Tărtăria tablets are three tablets discovered in 1961 in the village of Tărtăria (Hungarian: Alsótatárlaka).
This is about  from Alba Iulia in Romania.
The tablets, dated to around 5300 BC, have symbols in clay: the "Vinča symbols".
Some claim they are a yet undeciphered language.
If this is so, they would be the earliest known form of writing.
In 1908 similar symbols were found during excavations, by Miloje Vasić (1869–1956) in Vinča.
This is a suburb of Belgrade (Serbia), some 300 km from Turdaș.
Later, more were found in another part of Belgrade.
Since 1875 over one hundred and fifty Vinča sites have been found in Serbia alone.
Many, including Vinča itself, have not been fully excavated.
The culture of the whole area is called the Vinča culture.
Although some of these symbols look exactly the same as some letters in Etruscan, Greek, and Aramaic, they are generally regarded as an original, independent development.
It is only in the last 150 years that most people have been able to read and write in Europe and North America.
In many other parts of the world this did not happen until the 20th century.
Until then, literacy was mainly for clerics, that is, people who had training as priests.
Even wealthy people were often illiterate, and used scribes to write for them.
The invention of printing came before mass literacy.
Before 1500, each book had to be created by hand, so there were few books available compared to the billions in the world today.
Mass literacy needed cheap books.
The ordinary use of writing by means of a pen and paper.
Can refer to writing for oneself, as in a diary, but mostly it refers to sending letters.
Once it was almost the only means of communication between people who were separated.
Now, the telephone and e-mail are the most common means of distance communication.
kk:Жазу
rock (geology), a hard substance made of minerals, often found in or on the ground
Rock and roll music, a form of popular music that started in the 20th century
Plato was one of the most important classical Greek philosophers.
He lived from 427 BC to 348 BC.
A wealthy man, he owned at least 50 slaves and created the first university school, called "The Academy".
Plato was a student of Socrates (who did not write) and the teacher of Aristotle, who founded another university, known as the Lyceum.
Plato wrote about many ideas in philosophy that are still talked about today.
He wrote about ideas of deductive reasoning.
One modern philosopher, Alfred North Whitehead, said that all philosophy since Plato has just been comments on his works.
Plato wrote his books in the form of dialogues with two people or more talking about ideas, and sometimes disagreeing about them.
The Laws is Plato's longest dialogue and probably his last.
Socrates is usually the main person in Plato's dialogues.
Usually, Socrates talks with people about their ideas, and tries to see if they believe anything that is illogical.
Other people in the stories often become angry with Socrates because of this.
People who study Plato argue about whether Socrates really said the same things that Plato makes him say, or whether Plato just used Socrates as a character, to make the ideas he was talking about seem more important.
Plato opposed the rhetorics of sophism and insisted on true justice and equality in his work Gorgias, and on immortality of soul in Phaedo.
One of Plato's most famous works is The Republic (in Greek, Politeia, or 'city').
In that work, he describes Socrates's vision of an "ideal" state.
The method of questioning in this dialogue, called the Socratic method, is as important as the content.
The Republic contains ideas of Socrates: "Socrates said it, Plato wrote it."
Works by Plato
There are many dialogues that were supposed to be written by Plato.
This list includes those he probably did write.
427 BC births
340s BC deaths
Ancient Greek philosophers
A book is a set of printed sheets of paper held together between two covers.
The sheets of paper are usually covered with a text, language and illustrations.
The book is a more flexible format than the earlier idea of the scroll.
The change from scrolls to books began in the Roman Empire, and took many centuries to become complete.
A writer of a book is called an author.
Someone who draws pictures in a book is called an illustrator.
Books can have more than one author or illustrator.
A book can also be a text in a larger collection of texts.
That way a book is perhaps written by one author, or it only treats one subject area.
Books in this sense can often be understood without knowing the whole collection.
Examples are the Iliad, Odyssey, Bible and Torah.
All of them consist of a number of “books” in this sense of the word.
Encyclopedias often have separate articles written by different people, and published as separate volumes.
Each volume is a book.
Hardcover books have hard covers made of cardboard covered in cloth or leather and are usually sewn together.
Paperback books have covers of stiff paper and are usually glued together.
The words in books can be read aloud and recorded on tapes or compact discs.
These are called "audiobooks".
Books can be borrowed from a library or bought from a bookstore.
People can make their own books and fill them with family photos, drawings, or their own writing.
Some books are empty inside, like a diary, address book, or photo album.
Most of the time, the word "book" means that the pages inside have words printed or written on them.
Some books are written just for children, or for entertainment, while other books are for studying something in school such as math or history.
Many books have photographs or drawings.
Content of books
These books are novels, about stories that did not happen, and have been imagined by the author.
Some books are based on real events from history, but the author has created imaginary characters or dialogue for the events.
Books of non-fiction are about true facts or things that have really happened.
Some examples are dictionaries, cookbooks, textbooks for learning in school, or a biography (someone's life story).
Between the written manuscript and the book lie several inventions.
Manuscripts are hand-made, but books are now industrial products.
A common type of manuscript was the scroll, which was a long sheet rolled up.
The sheet could have been made of papyrus (made by the Egyptians, by weaving the inner stems of the papyrus plant and then hammering them together), or parchment or vellum (very thin animal skin, first used by the ancient Greeks), or paper (made from plant fibers, invented by the Chinese).
Manuscripts of this kind lasted to the 16th century and beyond.
Turning the manuscript into a book required several developments.
The codex
The Romans were the first people to put separate pieces of manuscript between covers, to form a codex.
This was more convenient to handle and store than scrolls, but was not yet a book as we understand it.
Scrolls and codices were written and copied by hand.
The Chinese invented woodblock printing, where shapes are carved out of a block of wood, then ink is applied to the carved side, and the block is pressed onto paper.
This woodcut method was slow because the symbols and pictures were made by cutting away the surrounding wood.
Johannes Gutenberg was the first to invent a machine for printing, the printing press, in the 15th century.
This involved more than just a press, it involved the production of movable metal type suitable for the machine process.
Initially, the machines were slow, and needed a printer's muscle to make them work.
The Industrial Revolution brought steam power and later electrification.
Paper and ink
Paper had been invented in China in the 8th century, but it was kept secret for a long time.
In Europe hand-made paper was available from about 1450.
It was cheaper than parchment but still expensive, and the early printing was a slow process.
Therefore, books remained rare.
In 1800 the first machines for making paper from wood pulp were invented.
New kinds of inks were also invented for various purposes, and machines were driven by steam engines and later by electricity.
The common cheap supply of paper fed the faster printing machines, and books became cheaper.
At the same time, in America, Britain and continental Europe, more people learnt to read.
So, in the 19th century, many ordinary people could afford to buy books and could actually read them.
Also in the 19th century came public libraries, so poorer people could get access to the best books.
Printing was done on large sheets of paper, which were then folded, guillotined (cut) and sewn into the covers.
Bookbinding and all the other processes have been done by machines since the 19th century.
Today some of the technologies have been changed, especially those involving illustration and typography.
However, books look much the same as they did, with more illustration in color, but basically the same.
That is because experience has shown that readers need certain things for pleasurable reading.
Graphic design and typography are the practical arts used to make books attractive and useful to readers.
WikiHow article on How to read a Book
Google Book Search (Beta)
Bestseller list of all times
History of printing
A sundial shows the current solar time during the day.
It does this because the sun appears to move through the sky.
At different times in the day when the sun is shining, a shadow is cast in different places on the dial.
A person marks the dial with the time at a certain shadow.
This lets users easily see the time.
There are a few commonly seen designs, such as the 'ordinary' or standard horizontal garden sundial.
However, sundials can be designed for any surface where a fixed object casts a predictable shadow.
They may be horizontal or vertical or tilted.
Ancient Egypt had sundials.
Other cultures developed them further, including the Greeks and Romans.
Sunbeams and Sundials Children's guide to the sun, the seasons and sundials.
There is a book from 1319 that talks about sundails
There is another old book from the 1500's that talks about how to make a sundial.
It's written in the Arabic language
A peninsula is a region of land that sticks out in a body of water.
It is also defined as a piece of land with water on three sides.
Many countries are on peninsulas, and may either take up part of a peninsula (such as Portugal) or all of it (such as India).
Parts of a country may also be on a peninsula.
For example, Jutland is a peninsula, as is Baja California in Mexico.
If Eurasia is considered a continent then the continent of Europe is technically a peninsula.
In this case, the great peninsulas of Europe, the Iberian, Italian, and Balkan peninsulas would technically be peninsulas within peninsulas.
The area of the European Peninsula, comprised of Europe minus Russia, Fennoscandia, and any islands, is roughly 4.4 million square kilometers.
Referencens
Derivative (linguistics), a word that is made from a more basic word
Derivative (chemistry), a substance that has similar properties to the original.
However, one or more components of the original are replaced
Derivative (finance), or derivative security
Derivative (mathematics), a central idea of calculus
Derivative works made from an existing work of art
Combinatorial game theory, also known as CGT is a branch of applied mathematics and theoretical computer science that studies combinatorial games, and is distinct from "traditional" or "economic" game theory.
CGT arose in relation to the theory of impartial games, the two-player game of Nim in particular, with an emphasis on "solving" certain types of combinatorial games.
A game must meet several conditions to be a combinatorial game.
The game must have at least two players.
The game must be sequential (i.e. Players alternate turns.)
The game must have perfect information (i.e. no information is hidden, as in Poker.)
The game must be deterministic (i.e. non-chance).
Luck is not a part of the game.
The game must have a defined amount of possible moves.
The game must eventually end.
The game must end when one player can no longer move.
These combinatorial games can be represented by trees, each vertex of which is the game resulting from a particular move from the game directly below it on the tree.
These games can be assigned game values.
Finding these game values is of great interests to CG theorists, as is the theoretical concept of game addition.
The sum of two games is the game in which each player on her/his turn must move in only one of the two games, leaving the other as it was.
Elwyn Berlekamp, John Conway and Richard Guy are the founders of the theory.
They worked together in the 1960s.
Their published work was called Winning Ways for Your Mathematical Plays.
In the theory, there are two players called left and right.
A game is something that allows left and right to make moves to other games.
For example, in the game of chess, there is a usual starting setup.
One could also, however, think of a chess game after the first move as a different game, with a different setup.
So each position is also called a game.
Games have the notation {L|R}.
are the games the left player can move to.
are the games the right player can move to.
If you know chess notation, then the usual chess setup is the game
Chess is very complex.
It is better to think of easier games.
Nim, for example, is much simpler to think about.
Nim is played like this:
There are zero or more piles of counters.
On a turn, a player may take as many counters from one pile as that player wants.
The player who cannot make a move loses.
The easiest game of Nim starts with no counters at all!
In such a case, neither player can move.
That is shown as {|}.
Both sides are empty, because neither player can move.
The first player to go cannot move, and so will lose.
In CGT, people often write {|} as the symbol 0 (zero).
The next-easiest game has only one pile, with just one counter.
If the left player goes first, that player must take the counter, leaving right with no moves ({|}, or 0).
If instead right moves first, there will be no more moves for left.
So both left and right can make a move to 0.
That is shown as {{|}|{|}}, or {0|0}.
The first player to move will win.
Games equal to {0|0} are very important.
They are written with the symbol, * (star).
Nim is a simple game used for examples in combinatorial game theory.
The rules of nim are simple:
The game begins with some piles of counters.
Players alternate turns.
On a turn, a player takes counters from a pile.
At least one counter must be taken, but up to 3.
All counters must be in the same pile.
If a player cannot take a counter, that player loses.
There is a simple mathematical strategy to play the game perfectly.
If both players play perfectly, the winner is determined by the initial setup.
cs:Rozšířená forma#NIM
Blue is one of the colors of the rainbow that people can see.
It is one of the seven colors of the rainbow along with red, orange, yellow, green, indigo and violet.
Apart from indigo and violet, it has the shortest wavelength of these colors (about 470 nanometers).
Blue is the color of the Earth's sky and sea.
Earth looks blue when seen from outer space by astronauts.
Blue is a color used to show coldness.
It is also one of the colors your lips can turn if you are chilly.
Blue is the color of a bluebird.
A blue jay is the color blue.
Meaning of blue
In Western cultures since the 1940s, blue is associated with men/boys, while pink is associated with women/girls.
Before the 1940s, it was the other way around, so blue was for women/girls and pink was for men/boys.
Nobody knows exactly why it changed.
Comparison of blue, indigo, violet and purple
Tones of blue color comparison chart
Blue-violet
Electric blue
Teal blue
Memory is the personal record of past experiences.
It is the brain's ability to store information to use later.
The Greeks considered memory (Mnemosyne) as the mother of Muses, for without her there would be no art and no science.
Short-term memory, the ability to keep information in mind for a short time, like remembering a phone number long enough to find a piece of paper.
Long-term memory, the ability to remember things long after they happen, like remembering a holiday you had last year.
Human skills
Murder is when one person kills another person on purpose.
If a person does something that makes someone else die, without the intention of killing, it is homicide and may be manslaughter.
An accident caused by carelessness may be negligent homicide.
Sometimes, a death caused by someone else may not be a crime, for example killing in self-defense.
A person who commits murder is called a murderer.
The legal definition of "murder" and "manslaughter" may be different between countries.
A killing in war is not usually called "murder" by those who fight in the war.
Killing in self defense is usually not "murder", but sometimes manslaughter.
Some countries do not even have manslaughter as a legal concept, and only have murder; the countries that do not have manslaughter charge with murder instead.
In fact, the United States did not have manslaughter on the books until the 20th century.
England was the first country to indoctrinate manslaughter, and the United States was second.
Most common circumstances for murder in the United States (1999)
Argument (unspecified) (3,391)
Robbery (1,010)
Juvenile gang killing (579)
Contravention of narcotic drug laws (564)
Argument over money or property (211)
Brawl due to influence of alcohol (187)
Romantic triangle (133)
Gangland killing (116)
Brawl due to influence of narcotics (111)
Burglary (79)
Worst cities for murder in the United States (1999)
New York's status as the murder capital of the world improved during the 1990s.
What follows are the number of murders for 1999:
New York, New York (671)
Chicago, Illinois (642)
Los Angeles, California (425)
Detroit, Michigan (415)
Philadelphia, Pennsylvania (292)
Houston, Texas (241)
Washington, D.C. (241)
Dallas, Texas (191)
New Orleans, Louisiana (158)
Atlanta, Georgia (143)
Attempted murder, or "attempt murder" in common law countries, also sometimes called "murder attempt", is when someone tries to kill another person.
Just planning a murder is not enough.
The act must come close to, but does not actually take the life of the other person.
It was punishable by death and the execution was carried out in Ancient Egypt, Ancient Mesopotamia, the Indus River Valley, Ancient Greece, The Roman Empire, and of course, China, which is by far the most populated country in the world, to this day.
As with murder, attempted murder is a mortal sin to the Catholic Church.
"Assassination" is a word which means murdering a prominent person for a reason.
The word is most used when the person who was killed was a celebrity or was a person involved in politics.
The people who carry out assassinations are called "assassins" or "Hit-men".
An assassin may murder someone for political reasons, for money, or for other reasons, such as favors owed and revenge.
Assassination is the same as murder and is mortal sin to the Catholic Church.
The word "Assassin" comes from Hashishin,  a Muslim group that was active in the Middle East from the 8th to the 14th centuries.
This secret society killed people for political and religious reasons.
It is thought that the assassins were under the influence of hashish and opium during their killings or during their training.
The word assassin comes from either hashashim, the influence of the drugs, or hassansin, after their leader, Hassan-i Sabbah.
Murdersuicide
No one is tracking the number of murder–suicides in the United States.
However, medical studies estimate between 1,000 and 1,500 deaths per year in the United States are murder-suicides.
Birds (Aves) are a group of animals with backbones which evolved from dinosaurs.
Technically speaking, they are dinosaurs.
Birds are endothermic.
The heat loss from their bodies is slowed down by their feathers.
Modern birds are toothless: they have beaked jaws.
They lay hard-shelled eggs.
They have a high metabolic rate, a four-chambered heart and a strong yet lightweight skeleton.
Birds live all over the world.
They range in size from the 5 cm (2 in) bee hummingbird to the 2.70 m (9 ft) ostrich.
They are the tetrapods with the most living species: about ten thousand.
More than half of these are passerines, sometimes known as perching birds.
Birds are the closest living relatives of the Crocodilia.
This is because they are the two main survivors of a once huge group called the Archosaurs.
Modern birds are not descended from Archaeopteryx.
According to DNA evidence, modern birds (Neornithes) evolved in the long Upper Cretaceous period.
More recent estimates showed that  modern birds originated early in the Upper Cretaceous.
Primitive bird-like dinosaurs are in the broader group Avialae.
They have been found back to the mid-Jurassic period, around 170 million years ago.
Many of these early "stem-birds", such as Anchiornis, were not yet capable of fully powered flight.
Many had primitive characteristics like teeth in their jaws and long bony tails.p274
The Cretaceous–Palaeogene extinction event 66 million years ago killed off all the non-avian dinosaur lines.
Birds, especially those in the southern continents, survived this event and then migrated to other parts of the world.
Diversification occurred around the Cretaceous–Palaeogene extinction event.
Birds have wings which are more or less developed depending on the species.
The only known groups without wings are the extinct moa and elephant birds.
Wings, which evolved from forelimbs, gave birds the ability to fly.
Later, many groups evolved with reduced wings, such as ratites, penguins and many island species of birds.
The digestive and respiratory systems of birds are also adapted for flight.
Some bird species in aquatic environments, particularly seabirds and some waterbirds, have evolved as good swimmers.
In general, birds are effective, and inherit their behaviour almost entirely.
The key elements of their life are inherited.
It was a great discovery that birds never learn to fly.
So it is quite wrong to say, when a chick waves its wings in the nest "It's learning to fly".
What the chick is doing is exercising its muscles.
They develop the ability to fly automatically (assuming they are species that do fly).
And if they are species which migrate, that behaviour is also inherited.
Many species migrate over great distances each year.
Other main features of their life may be inherited, though they can and do learn.
Birds have good memories which they use, for example, when they search for food.
Several bird species make and use tools.
Some social species pass on some knowledge across generations, a form of culture.
Birds are social.