the-french-artist/wikipedia_20220301.simple_sentence_split huggingface dataset:
Asia - Lake Baikal is the largest lake that is completely in Asia.
The Caspian Sea, the largest lake on Earth, is on the Europe-Asia border (an artificial border) and so both continents share this lake.
Australia - Lake Eyre, that most of the time is without water; it takes water when it rains a lot.
Europe - Lake Ladoga, followed by Lake Onega, both in northwestern Russia.
North America - Lake Superior.
South America - Lake Maracaibo but it is like a bay because it has a wide opening to sea.
The largest freshwater lake of South America is Lake Titicaca, which is also the highest body of water on Earth at 3,821 m (12,507 ft) above sea level where boats can travel.
Notable lakes
The largest lake in the world by area is the Caspian Sea, with 394,299 km².
The largest freshwater lake by area is Lake Superior (82,414 km²), part of the Great Lakes.
The longest freshwater lake is Lake Tanganyika, with a length of about 660 km.
Lake Baikal is the second longest (about 630 km from tip to tip).
The deepest lake is Lake Baikal in Siberia, with a bottom at 1,637 m (5,371 ft).
Lake Tanganyika (1,470 m) is the second deepest lake.
The highest lake of the world is a small lake (pond) without a name on Ojos del Salado at 6,390 m (20,965 ft).
But the highest navigable lake is Lake Titicaca in Peru and Bolivia at 3,812 m (12,507 ft).
The lowest lake of the world is the Dead Sea, bordering Israel and Jordan at 418 m (1,371 ft) below sea level.
It is also one of the lakes with highest salt concentration.
Lake Enriquillo in Dominican Republic is the only saltwater lake in the world where crocodiles live.
Something that is from or related to France
The French language
French people
French cuisine
East is one of the 4 main directions on a compass (called cardinal directions).
East is normally to the right on most maps.
For example: Japan is east of China, which is itself east of Pakistan.
When “The East” is described: it usually refers to the countries of Asia (especially from Pakistan eastwards like China and India).
The sun and moon are also seen to rise in the east.
A tire is a ring of material that covers the rim of a wheel.
Most road vehicles and many other vehicles use rubber tires.
Tires help vehicles to move smoothly.
Some metro trains and trams also use rubber tires on their steel wheels to provide better traction than the steel tires of other trains.
Tires need to be changed after their treads wear away.
Driving with worn tires is very dangerous.
It can cause the tire to explode and the driver to lose control.
Tires were made of leather for thousands of years, and of iron or steel for hundreds.
Pneumatic tires were invented in the 1840s and again in the 1880s.
They became commonplace early in the 20th century.
Tires are made of different types of rubber.
Softer rubber is used in summer or when the tires need better traction, for example, in auto racing.
Tires made of harder rubber are made for long lasting performance, like long-distance truck carriers.
There are many different types of tires.
They come in different sizes and have different tread patterns.
There are many different sizes of tires.
On car and truck tires, they are marked with 3 numbers and might look like: 225/60R16.
The first number is the width in millimeters of the tire at the widest point when it is mounted and inflated.
The second number is the sidewall (side of the tire) height as a ratio or percentage of the width.
The last number is the wheel diameter in inches.
Tire width = 225mm
Sidewall height = 135mm (225 * .60 = 135)
Wheel diameter = 16 inches
Very large tires (for example, tires on big mining trucks) use different units.
For example: 59/80R63.
The first number is the width in inches of the tire.
The second number is the sidewall height as a ratio of the width.
Tire damage
Most tires today do not have a tube inside of them.
There are grooves in the wheel that let the tire be popped into place and hold a lot of air pressure.
If there is a crack in the tire, it will not be able to hold its air.
Tire leaks are very common.
The most common cause is a hole from a nail or screw.
This can usually be fixed by patching the inside of the tire so that it can hold air again.
If the hole is close to or in the side of the tire, it can not be fixed.
This is because the sides of the tire flexes to support the weight of the vehicle.
A patch will not be able to handle the stress.
Mud and snow tires
Mud and Snow, (or M+S, or M&S), is a designation used by manufacturers for all-season and winter tires.
Most are designed to provide improved performance under low temperature conditions, compared to summer tires.
The tread compound is usually softer than that used in tires for summer conditions.
This provides better grip on ice and snow, but wears more quickly at higher temperatures.
Tires may have well above average numbers of sipes in the tread pattern to grip the ice.
M&S relates to the percentage of tread void area.
On four-wheel drive vehicles, M&S tires are often standard equipment.
A population is the number of living people that live together in the same place.
A city's population is the number of people living in that city.
These people are called inhabitants or residents.
The population includes all individuals that live in that certain area.
The world population was estimated to have reached 7.5 billion in April 2017.
Asia is the most populous continent, with its 4.3 billion inhabitants being 60% of the world population.
The most populous country is China with 1.4 billion people.
Population density is the average number of people in a place.
Urban areas such as big cities have a high population density.
People there live close to each other.
In areas with a low population density, people usually live far away from each other, such as in rural areas out in the countryside.
Usually population refers to the number of humans in a certain area.
The maximum population that can be supported in an area is called the carrying capacity.
Population trends
Global population is going up, but the population growth rate is declining all over the world.
Growth in poor countries is faster than in rich ones; some rich countries have a population pyramid that is nearly square.
Urbanization is also common, and urban areas usually have lower birth rates.
In population growth, births exceed deaths.
In the modern world this is due to reduction of infant deaths, control of infectious diseases, and improved agriculture so more people can eat.
World: +420 million
Africa: +146 million
Asia: +223 million
Europe: +3 million
Latin America and Caribbean: +35 million
Northern America: +14 million
Oceania: +2.9 million
Human population control is the practice of altering the rate of growth of a human population.
Concerns about overpopulation and its effects on poverty, environmental degradation, and political stability led to efforts to reduce population growth rates.
YAN Kun(2011).
The tendency equation of the population and its limit value in the United Kingdom (Brief annotation of the connection equation(R)), Xi'an: Xi'an Modern Nonlinear Science Applying Institute.
Snow is a form of ice.
Snow forms when water in the atmosphere becomes frozen.
Snow comes in all different shapes and sizes.
At the freezing point of water (0° Celsius, 32° Fahrenheit), snow melts and becomes liquid water.
Sometimes, the snow will melt very fast and become water vapor.
This is called sublimation.
The opposite, where water vapor becomes snow, is called deposition.
Snow is used for some winter sport activities like skiing and sledding.
Sometimes people make artificial snow so they can ski.
People also commonly build things out of snow for fun.
Snow can also be dangerous, as it can lower visibility and make driving very difficult.
When it snows, the snow will melt a little during the daytime and freeze again at night.
This makes ice which can make driving conditions very treacherous.
Snow plows are used to remove snow from roads to make driving easier and safer.
Also, sand or salt may be added to the road to help tires grip the road.
When salt is mixed with snow, the snow will melt more easily.
This is because salt water has a lower melting point than fresh water (water without salt).
A blizzard is a dangerous type of a snowstorm.
A blizzard produces strong winds that keep the snow in the air, thus reducing visibility.
Sometimes it produce thunder snow, which is snow with lightning and thunder.
West is one of the 4 main directions on a compass.
West is normally to the left on most maps.
For example: (Germany is located to the west of Poland, which is itself located to the west of Lithuania).
When “The West” is used in everyday speech: it usually refers to the nations of Europe (Especially from Croatia Westward) and its daughter states in the Americas and Australasia.
The sun and moon also set in the west.
Rarefaction -- Ray box -- Reflection -- Refraction -- Ripple tank  --
A president is the leader of a country or a company or other group.
A president is usually elected by the people in that group.
Voting is one way to elect a president.
Electing a President
The President of the United States is elected by the electoral college.
Some other countries choose a president this way.
In some, the Parliament does it.
Some countries have direct elections to choose a president.
Many countries have a monarch instead of a president and some have neither.
Companies have presidents.
They are elected by the people who own part of the company.
In some companies, the people who are workers for the company elect (vote for) their company president.
Power of a President
The president of a country is not the same thing as a prime minister.
A prime minister is part of a parliament, but a president is not.
In some countries, (such as the United States or France), the president has more power and responsibility than anyone else.
Such a president is often called the nation's chief executive.
As chief executive, the president must take an active role in all phases of government.
In other countries (such as India, Israel or the Republic of Ireland), to be president is more of an honor or a symbol, and the position has no real power.
This kind of president is often called "head of state".
The American President is restricted by the written United States Constitution, which was written to make sure that the American executive never became as powerful as in the British system.
The British Prime Minister is part of both the Legislature and Executive, whereas the American President is the head of the Executive.
The American governmental system shows a clear separation of powers unlike the British system.
All the president's ministerial appointments have to be vetted by Congress (Parliament) and Congress may have an opposition majority.
The president does not have the ability to introduce and influence legislation in the same way as the British prime minister.
Congress has much greater control over the budget and foreign policy than the British Parliament.
There are broad areas of American life, such as education, crime and punishment, over which the president has virtually no influence at all.
The president even has very limited control over the economy.
Presidents of the United States
International Lakes in Africa
Lake Albert (Mobuto-Sese-Seko)
Lake Edward
Lake Nyasa (Lake Malawi)
in Democratic Republic of the Congo (Zaire)
Lake Mai-Ndombe (Lake Leopold II)
Lake Tshangalele
Lake Tumba
in Egypt
Lake Mariout
in Ethiopia
Lake Abaya
Lake Chew Bahir (Lake Stefanie)
Lake T'ana
in Ghana
Lake Volta
in Kenya
Lake Baringo
Lake Elmenteita
Lake Naivasha
Lake Nakuru
Lake Turkana (Lake Rudolf or Rudolph)
in Malawi
Lake Chilwa
in Mozambique
Cabora Bassa Lake
in Nigeria
Kainji Lake
in Tanzania
Lake Burigi
Lake Eyasi
Lake Ikimba
Lake Jipe
Lake Kitangiri
Lake Manyara
Lake Mdutu
Nyumba ya Mumgu Reservoir
Lake Sagara
in Uganda
Lake Bisina
Lake Kyoga
Lake Kwania
in Zambia
Lake Mweru Wantipa
Lake Bangweulu
Lake Vida
International Lakes in Asia
in Cambodia
Tonlé Sap Lake
in China ( See also Lakes in China)
Lake Daze Co
Lake Dongting
Lake Tianchi
Lake Dian
Lake Qinghai
Lake Taihu
Sea of Galilee (Lake Tiberias, Yam Kinneret)
Lake Agmon
Lake Ram
Swamps Cabara
in Kazakhstan
Lake Balkhash
Lake Zaysan
in Kyrgyzstan
Issyk Kul
in Nepal
in Russia (see also "in Russia" under #Europe, List of lakes in Russia)
Lake Baikal (Lake Baykal)
Lake Teletskoye
in Taiwan
in Turkey
International Lakes in Europe
Lake Geneva (France, Switzerland; Lac Léman or Lac de Genève)
Lake Constance (Austria, Germany, Switzerland; Bodensee)
Lake Peipus (Estonia, Russia)
Lake Ohrid (Albania, Macedonia)
Lake of Lugano (Switzerland, Italy)
Lake Maggiore (Switzerland, Italy; Lago Maggiore)
Lake Ferto/Lake Neusiedler (Austria, Hungary; Neusiedlersee)
Lake Big Prespa (Albania, Macedonia, Greece)
Lake Small Prespa (Albania, Macedonia, Greece)
Lake Vistytis (Lithuania, Russia)
in Albania (see also: List of Albanian lakes)
Lake Shkodër
Lake Pogradec
Lakes of Lure
Lakes of Belsh
in Austria
Lake Attersee
Lake Klopeiner
Lake Wörther
in Finland
Lake Haukivesi
Lake Inarinjärvi
Lake Kallavesi
Lake Oulujärvi
Lake Pielinen
Lake Pihlajavesi
Lake Päijänne
Lake Annecy (lac d'Annecy)
Lac de Serre-Ponçon
Lake of Bourget
Lac de Paladru
Lac d'Orient
Arendsee
Aussenalster
Baldeneysee
Bederkesaer See
Binnenalster
Brahmsee
Bullensee
Dümmer
Fleesensee
Gothensee
Halterner See
Kellersee
Lake Constance (Bodensee)
Maschsee
Müggelsee
Odertalsperre
Okertalsperre
Pfaffenteich
Plöner See
Scharmützelsee
Schmollensee
Tegeler See
Wannsee
Wolgastsee
Zwischenahner Meer
in Hungary
in Ireland (see also List of Irish lochs and loughs)
Lough Allen
Lough Conn
Lough Derg (two lakes)
Lough Erne (two lakes)
Lough Mask
Lough Owel
Lough Ree
Lough Rynn
Lake Bracciano (Lago di Bracciano)
Lake Bolsena (Lago di Bolsena)
Lake Como (Lago di Como)
Lake Garda (Lago di Garda)
Lake Trasimeno (Lago Trasimeno)
in Latvia
Lake Burtnieks
in Netherlands
IJsselmeer
Ketelmeer
Veluwemeer
in Poland
Lake Dabie (Jezioro Dabie in Szczecin)
Lake Mamry (Jezioro Mamry in Mazury lake district)
Lake Sniardwy (Jezioro Sniardwy in Mazury lake district)
in Romania
in Russia (see also "in Russia" under #Asia, List of lakes in Russia)
Lake Onega (Onega, Onezhskoe ozero, Onezhskoe)
Lake Pskov
in Slovenia
Lake Bled (Blejsko jezero)
Lake Bohinj (Bohinjsko jezero)
Cerkni?ko jezero
martinsko jezero
Lakes of Triglav (Triglavska jezera)
Lake Roxen
in Switzerland (see also List of lakes of Switzerland)
in the United Kingdom (see also List of Scottish lochs, List of lakes in the Lake District)
Bala Lake
Derwentwater
Gwernan Lake
Kielder Water (Northumberland, England)
Loch Awe/Etive
Loch Shin
Loch Tay
Tal-y-llyn
Thirlmere
International Lakes in North America
Lake Erie †
Lake Huron †
Lake Nicaragua (Lake Cocibolca)
Lake Ontario †
Lake Superior †
in Canada
Lake Abitibi
Lake Athabasca
Berg Lake
Manicouagan Reservoir
Lake Manitoba
Moraine Lake
Lake Nipigon
Reindeer Lake
Lac Saint-Louis
Smallwood Reservoir
Sproat Lake
Lake Winnipegosis
in the United States of America
Beaver Lake
Lake Bemidji
Caddo Lake
Canandaigua Lake
Cass Lake
Cayuga Lake
Chargoggagoggmanchauggagoggchaubunagungamaugg
Detroit Lake
East Okoboji Lake
Indian Lake (Ohio)
Lake Hopatcong
Lake Itasca
Keuka Lake
Lake Kickapoo
Lacamas Lake
Lake Mead
Lake Michigan †
Portage Lake
Lake Sammamish
Seneca Lake
Town Lake
Lake Travis
Tug Lake
West Okoboji Lake
Lake Winnipesaukee
Lake Winnebago
in Australia
in Indonesia
Lake Toba (on Sumatra)
In New Zealand (minor lakes not listed)
In the North Island
Mount Ruapehu's Crater Lake on Mount Ruapehu
Lake Waikaremoana
Lake Wairarapa
In the South Island
Lake Aviemore
Lake Benmore
Lake Brunner
Lake Coleridge
Lake Ellesmere
Lake Hauroko
Lake Manapouri
Lake Monowai
Lake Ohau
Lake Rotoiti
Lake Rotoroa
Lake Sumner
Lake Waitaki
Lake Wakatipu
Lake Wanaka
(Not yet classified by country:)
International Lakes in South America
Former lakes
Fictional lakes
Lake Evendim
Lake Mithrim
Galileo Galilei (15 February 1564 – 8 January 1642) was an Italian polymath.
Galileo was originally going to be a doctor but became a tutor instead.
He was a professor of mathematics and natural science in Padua and Pisa.
People most remembered him today for his conflict with the Catholic Church of his day, which led to his trial for heresy by the Inquisition.
Galileo was born on 15 February 1564 in Pisa, Duchy of Florence.
He was the eldest of five siblings.
His father was Vincenzo Galilei, who was a scholar and a musician.
In 1574, the Galileo family moved to Florence and he started his formal education in the Camaldolese monastery.
Some people believe that Galileo was the first person to build a telescope.
This is not true, but he was the first person to publish his observations of astronomical objects through a telescope.
He discovered that the Milky Way is made of many stars.
He discovered that the Moon has hills.
He found four moons around Jupiter.
Those moons are now called the Galilean moons.
He discovered sunspots, which are dark areas of the Sun.
He saw that the planet Venus has light and dark phases just like the Moon.
This helped people to know that the Sun is at the centre of the Solar System, as Nicolaus Copernicus had said.
Galileo worked more at physics than at astronomy.
He studied natural forces, and was one of the most important discoverers of the part of physics that is now called kinematics, including the discovery of the kinematic principle of relativity.
However, he is often remembered now for things that either did not happen, or failed.
A legend says that he climbed the Leaning Tower of Pisa, and dropped cannonballs of different weights, to see which would strike the ground first.
Even though their weights were not the same, they hit the ground at the same time.
Galileo found that objects fall to the ground at the same rate, unless things like wind resistance change the rate.
This went against the views of Aristotle, an ancient philosopher whose theory was different.
Galileo's findings were ignored by most people, and Aristotle's view was still accepted as correct until Isaac Newton proved Galileo was right.
This also led to Newton creating his Law of Gravity.
Galileo also tried to determine the speed of light.
He climbed a hill, and had an assistant climb another hill, both carrying lanterns with closed shutters.
He then opened the shutter of his lantern.
His assistant opened his own shutter when he saw Galileo's lantern.
Galileo then measured the time it took for his assistant's shutter to open.
Knowing the time difference, and the distance between the hills, he tried to estimate the speed of light.
However, this did not work.
Siderius nuncius (starry messenger).
Venice 1610.
Discovery of 'new worlds' with the telescope.
Dialogo sopra i due massimi sistemi del mondo, Tolemaico et Copernicano.
Florence, 1632.
The famous 'dialogue between two world systems, Ptolemaic and Copernican'.
Discorsi et demonstrazioni mathematiche, intorno a due nuove scienze. (
discourses and mathematical demonstrations relating to two new sciences) Leiden 1638.
This, on kinematics, a non controversial subject, was written when Galileo was under house arrest, and published in Holland, out of the Inquisition's territory.
Trial for heresy
Galileo came to accept the findings of Copernicus, that the Sun was the center of the then-known universe, and not the Earth.
Because he promoted this and other ideas, he came to the notice of the Committee of Propaganda, the dreaded Inquisition.
The Church taught that the Earth stood still, while everything in the sky moved around it.
The Inquisition ruled in 1616 that other theories could only be discussed as possibilities, not facts.
Galileo said he would obey.
He played a major part in the scientific revolution through this argument.
Galileo later discussed the question in his most famous work, Dialogue Concerning the Two Chief World Systems, published in 1632 by permission of the Inquisition.
His scientific writing was usually in Latin for hundreds of scientists around Europe, but this was one of the books he wrote in Italian so thousands of Italians could read it.
The book was in the form of conversations between three men.
The man representing the Church's point of view was called 'Simplicio'.
Church leaders who liked his earlier books were angry at this one.
The Inquisition took action in 1633.
He was arrested and put on trial.
They found him "vehemently suspect of heresy".
They reminded him of the fate of Giordano Bruno, who had been burnt at the stake for heresy on topics such as transubstantiation and the Trinity.
Bruno also believed the Earth went round the Sun and stars had planets.
The Inquisition forced Galileo to recant (say he was wrong) under the threat of execution, and to withdraw his works from publication.
Galileo spent the last ten years of his life under house arrest.
Galileo continued to write about physics and other topics, but not astronomy.
Galileo has become synonymous with a warrior for scientific truth.
Although he had to retract his writings at his trial, it is widely believed that after the trial he insisted that Earth does move around the sun, saying the famous phrase "Eppur si muove''' – still it moves.''
The saying itself became a slogan for science.
Galileo Galilei died on  in Arcetri, Grand Duchy of Tuscany, Italy.
Previously, he was buried in a small room next to the novices' chapel at the end of a corridor.
Later, he was reburied in the main body of the basilica in 1737 after a monument had been built there in his honour.
List of science books of 17th century
1564 births
1642 deaths
Italian astronomers
People from Pisa
Italian physicists
An agreement is writing down a promise made.
Agreements are common in law and business.
For example, when a person takes out a loan or hires someone to work, an agreement is usually signed so that everyone understands what and when things must be done.
When a person agrees to do something or to not do something, that person is making a promise.
A promise can be made   (by saying it), or it can be written down as a contract.
Breaking a promise, or not keeping it, is often just bad manners, but it can sometimes be illegal, such as when a contract is not kept.
A vow is a special promise.
It is mostly used in a religious sense or in ceremonies such as marriages when the couple who are being married make their "marriage vows", promising to be faithful to one another.
An oath is a promise in the legal sense.
When someone has to give evidence in a court of law they "swear an oath".
This means that they promise they will tell the truth.
Water on the Earth evaporates (turns into an invisible gas) and rises up into the sky.
Higher up where the air is colder, the water condenses: it changes from a gas to drops of water or crystals of ice.
We see these drops of water as clouds.
The drops fall back down to earth as rain, and then the water evaporates again.
This is called the "water cycle".
The atmosphere always has some water vapour.
Clouds form when the atmosphere can no longer hold all the invisible air vapor.
Any more water vapor condenses into very small water drops.
Warm air holds more water vapor than cool air.
So if warm air with lots of water inside cools, it can form a cloud.
These are ways air can cool enough to form clouds:
when air close to the ground is heated by the sun and rises to where the air is colder.
along weather fronts warmer air is cooled as it runs into colder air;
when air goes up the side of a mountain it cools as it goes higher;
when warm air goes over something colder such as cool water in a lake) or ground that is cooled at night it cools.
Clouds are heavy.
The water in a cloud can have a mass of several million tons.
Every cubic metre (m3) of the cloud has only about 5 grams of water in it.
Cloud droplets are also about 1000 times heavier than evaporated water, so they are much heavier than air.
They do not fall, but stay in the air, because there is warm air all round the heavier water droplets.
When water changes from gas to droplets, this makes heat.
Because the droplets are very small, they "stick" to the warm air.
Sometimes, clouds appear to be brilliant colors at sunrise or sunset.
This is due to dust particles in the air.
Cloud classification
Clouds are classified according to how they look and how high the base of the cloud is in the sky.
This system was suggested in 1803.
There are different sorts of clouds because the air where they form can be still or moving forward or up and down at different speeds.
Very thick clouds with large enough water droplets can make rain or snow, and the biggest clouds can make thunder and lightning.
Cirrus clouds are high and thin.
The air is very cold at high levels, so these clouds are made of ice crystals instead of water droplets.
Cirrus clouds are sometimes called mares' tails because they look like the tails of a horse.
Stratus clouds are like flat sheets.
They may be low-level clouds (stratus), medium-level (altostratus), high-level (cirrostratus), or thick multi-level clouds that make rain or snow (nimbostratus).
Stratocumulus clouds are in the form of rolls or ripples.
They may be low-level clouds (stratocumulus), medium-level (altocumulus), or high-level (cirrocumulus).
Cumulus clouds are puffly and small when they first form.
They may grow into heap clouds that have moderate vertical extent (nothing added to the name), or become towering vertical clouds (towering cumulus).
Cumulonimbus clouds are very large cumulus-type clouds that usually develop cirrus tops and sometimes other features that give them their own unique look.
High-Level clouds
High clouds form from  in cold places,  in mild regions and  in the very hot tropics.
They are too high and thin to produce rain or snow.
Cirrus (Ci)
Cirrocumulus (Cc)
Cirrostratus (Cs)
Medium-level clouds
Middle clouds usually form at  in colder areas.
However, they may form as high as  in the tropics where it's very warm all year.
Middle clouds are usually made of water droplets but may also have some ice crystals.
They occasionally produce rain or snow that usually evaporates before reaching the ground.
Altocumulus (Ac)
Altostratus (As)
Low-level clouds
Low-level clouds are usually seen from near ground level to as high as .
Low clouds are usually made of water droplets and may occasionally produce very light rain, drizzle, or snow.
Stratocumulus (Sc)
Stratus (St)
Moderate-vertical clouds
These are clouds of medium thickness that can form anywhere from near ground level to as high as .
Medium-level cumulus does not have alto added to its name.
The tops of these clouds are usually not much higher than .
Vertical clouds often create rain and snow.
They are made mostly of water droplets, but when they push up through cold higher levels they may also have ice crystals.
Cumulus (Cu)
Nimbostratus (Ns)
Towering-vertical clouds
These clouds are very tall with tops usually higher than .
They can create heavy rain and snow showers.
Cumulonimbus, the biggest clouds of all, can also produce thunderstorms.
These clouds are mostly made of water droplets, but the tops of very large cumulonimbus clouds are often made mostly of ice crystals.
Towering cumulus (Tcu)
Cumulonimbus (Cb)
As a sign
Water is essential for life as we know it.
It is present throughout the Solar System, and was part of the Earth from its formation.
The source of the water was the same as the source of the Earth's rock : the cloud particles which condensed in the origin of the solar system.
The cycle starts when water on the surface of the Earth evaporates.
Evaporation means the sun heats the water which turns into a gas.
Then, water collects as water vapour in the sky.
This makes clouds.
Next, the water in the clouds gets cold.
This makes it become liquid again.
This process is called condensation.
Then, the water falls from the sky as rain, snow, sleet or hail.
This is called precipitation.
The water sinks into the surface and also collects into lakes, oceans, or aquifers.
It evaporates again and continues the cycle.
Humans activities that affect the water cycle
Building dams
Removing groundwater from wells
Water abstraction from rivers
Water vapor is water that is in the form of a vapor, or gas.
It is a part of the water cycle.
When liquid water is heated to boiling point, 100 degrees Celsius (212 F), it turns into vapor.
Water vapor can also be produced directly from ice; this is called sublimation.
Steam is water vapor, but clouds are liquid water.
The amount of water vapor in air is called humidity and it affects weather conditions.
In the cold, breathing out causes the water vapor in the breath to freeze.
Water vapour is transparent.
The small droplets that look white like mist are actually liquid.
Solid is one of the three common states of matter.
The molecules in solids are closely bound together, they can only vibrate.
This means solids have a definite shape that only changes when a force is applied.
This is different to liquids and gases which move randomly, a process called flow.
When a solid becomes a liquid, this is called melting.
Liquids become solid by freezing.
Some solids, like dry ice, can turn into gas without turning liquid first.
Kinds of solids
The forces between the atoms in a solid can take many forms.
For example, a crystal of sodium chloride (common salt) is made up of ionic sodium and chlorine, which are held together by ionic bonds.
In diamond or silicon, the atoms share electrons and make covalent bonds.
In metals, electrons are shared in metallic bonding.
Some solids, like most organic compounds, are held together with "van der Waals forces" coming from the polarization of the electronic charge cloud on each molecule.
The dissimilarities between the types of solid come from the differences between their bonding.
Most metals are strong, dense, and good conductors of electricity and heat.
The mass of the elements in the periodic table, those to the left of a diagonal line drawn from boron to polonium, are metals.
Mixtures of two or more elements in which the big component is a metal are known as alloys.
The strength and relialbility of metals has led to their widespread use in making of buildings and other things, as well as in most vehicles, many tools, pipes, road signs and railroad tracks.
Iron and aluminium are the two most commonly used metals.
They are also the most common metals in the Earth's crust.
Iron is most commonly used in the form of an alloy, steel, which has up to 2.1% carbon, making it much harder than pure iron.
Since metals are good conductors of electricity, they are valuable in electrical tools and for carrying an electric current over long distances with little energy loss.
Because of this, electrical power grids rely on metal cables to get electricity.
Home electrical systems, for example, are wired with copper for its good conducting uses.
The high thermal conductivity of most metals also makes them useful for stovetop cooking utensils.
Minerals are natural solids formed through many geological processes under high pressures.
To be thought as a true mineral, a substance must have a crystal structure with uniform physical things throughout.
Minerals differ in composition from pure elements and simple salts to very complex silicates with thousands of known forms.
In contrast, a rock sample is a random aggregate of minerals and/or mineraloids, and has no specific chemical composition.
Most of the rocks of the Earth's crust have quartz (crystalline SiO2), feldspar, mica, chlorite, kaolin, calcite, epidote, olivine, augite, hornblende, magnetite, hematite, limonite and a few other minerals.
Some minerals, like quartz, mica or feldspar are common, while others have been found in only a few places in the world.
The largest group of minerals by far is the silicates (most rocks are ≥95% silicates), which are made largely of silicon and oxygen, also with ions of aluminium, magnesium, iron, calcium and other metals.
Evaporation is when a liquid becomes a gas without forming bubbles inside the liquid volume.
If bubbles are formed we are talking instead about "boiling".
For example, water left in a bowl will slowly disappear.
The water evaporates into water vapor, the gas phase of water.
The water vapor mixes with the air.
When the molecules in a liquid are heated, they move faster.
This makes them full of energy and so the particles collide with each other, and eventually they become so far apart that they become a gas.
Differences between evaporation and boiling
During evaporation only the molecules near the liquid surface are changing from liquid to vapor.
During boiling the molecules inside the volume of the liquid are also changing to vapor.
For this reason during evaporation no bubbles are formed, instead they are formed during boiling.
Evaporation can happen at any temperature, while boiling happens only at a specified temperature called the "boiling point".
Evaporation happens slowly, but boiling happens quickly.
Rate of evaporation
Some liquids evaporate more quickly than others.
There are many factors that affect the evaporation rate.
A contract is an agreement or promise that the law can enforce.
The law will enforce some agreements but not others.
For example, in most places, if a parent promises to take a child to get ice cream, the law will not enforce that promise as a legal contract.
Sometimes, a contract is written down and signed by the people agreeing to it, but it does not always need to be.
People usually sign a contract when something important or costly is being done.
For example, when people take a job, they will sometimes sign a contract with their employers.
The contract will show what the person must do as part of his job, how much they will be paid, and so on.
The person and the employer will sign the contract, and it will become a legal promise.
If someone breaks a contract, another person might sue him or her.
In a lawsuit about a contract, the court will look at the contract, listen to what the people who made the contract say about it, and then make a decision about what the contract means.
It is the part of us that others interact with.
On the face are organs of sight, smell, hearing.
Especially in a four-legged animal, the face is the part which goes first into the world, and that is why the sense organs and the mouth are there.
Kolkata (spelled Calcutta before 1 January 2001) is the capital city of the Indian state of West Bengal.
It is the second largest city in India after Mumbai.
It is on the east bank of the River Hooghly.
When it is called Calcutta, it includes the suburbs.
This makes it the third largest city of India.
This also makes it the world's 8th largest metropolitan area as defined by the United Nations.
Kolkata served as the capital of India during the British Raj until 1911.
Kolkata was once the center of industry and education.
However, it has witnessed political violence and economic problems since 1954.
Since 2000, Kolkata has grown due to economic growth.
Like other metropolitan cities in India, Kolkata struggles with poverty, pollution and traffic congestion.
The discovery of the nearby Chandraketugarh, an archaeological site has proved that people have lived there for over two millennia.
The history of Kolkata begins when the English East India Company arrived in 1690.
Job Charnock, an administrator with the Company is traditionally known as the founder of this city.
However some academics say that Charnock is not the city's founder.
At that time Kolkata, ruled by the Nawab of Bengal Siraj-Ud-Daulah, had three villages.
They were Kalikata, Govindapur and Sutanuti.
The British in the late 17th century wanted to build a fort near Govindapur.
This was to become more powerful than Dutch, the Portuguese, and the French.
In 1702, the British completed the construction of old Fort William, which was used to station its troops and as a regional base.
Calcutta was declared a Presidency City, and later became the headquarters of the Bengal Presidency.
When regular fights with French forces started, in 1756 the British began to upgrade their fortifications.
When this was protested, the Nawab of Bengal Siraj-Ud-Daulah attacked and captured Fort William.
This led to the infamous Black Hole incident.
A force of Company sepoys and British troops led by Robert Clive recaptured the city the next year.
Calcutta became the capital of British India in 1772,.
However, the capital shifted to the hilly town of Shimla during the summer months every year, starting from the year 1864.
Richard Wellesley, the Governor General between 1797–1805, helped in the growth of the city and its public architecture.
This led to the description of Calcutta as "The City of Palaces".
The city was a centre of the British East India Company's opium trade during the 18th and 19th century; locally produced opium was sold at auction in Kolkata, to be shipped to China.
Former national capitals
A pencil is a kind of writing equipment that is also used to draw, usually on paper.
Most pencil cores are made of graphite powder mixed with a clay binder.
So, a pencil is usually made with a piece of graphite mixed with clay that has a wood case around it.
The shape is usually a hexagonal prism but some pencils are square or cylinder.
Colored pencils are a kind that do not use greyish silver graphite.
Instead, the core is colorful.
Colored pencils or crayons are usually meant for drawing rather than writing.
The difference between pens and pencils
The important difference between pens and pencils is that the tip of a pencil is made of solid graphite (or other material) which is rubbed off onto the paper.
A pen has a tip, usually made of metal, with liquid ink coming out and onto the paper.
Writing with a pen can smudge when it is still wet.
Writing from a pencil can be erased, but writing from a pen usually cannot, unless it uses a special type of ink and eraser.
Another early writing instrument was the stylus, which was a thin stick of wood or metal, often lead.
It was used for scratching onto black wax that covered white wood, a method used by the Romans.
The word pencil comes from the Latin word  which means "little tail".
It is an invention of the 16th century in England.
Discovery of graphite deposits
Some time before 1565 (it may have been as early as 1500), a large deposit of graphite was found in Borrowdale, Cumbria.
The locals found that it was very useful for marking sheep.
This deposit of graphite was extremely pure and solid, and it could easily be sawn into sticks.
This is still the only large scale deposit of graphite ever found in this solid form.
Chemistry was in its early stages and the substance was thought to be a form of lead.
Consequently, it was called plumbago (Latin for "lead ore").
The black core of pencils is still  referred to as lead, even though it never had the element lead.
The value of graphite was soon realized, mainly because it could be used to line the moulds for cannonballs.
The mines were taken over by the Crown and guarded.
When enough stocks of graphite had been added up, the mines were flooded to prevent theft until more was needed.
Graphite had to be sneakily moved out for use in pencils.
Because graphite is soft, it requires some form of holder.
Graphite sticks were at first wrapped in string or in sheepskin for stability.
The news of the usefulness of these early pencils spread far and wide, attracting the attention of artists all over the known world.
England continued to have a monopoly on the production of pencils until a method of reconstituting the graphite powder was found.
The distinctively square English pencils continued to be made with sticks cut from natural graphite into the 1860s.
The town of Keswick, near the original findings of block graphite, has a pencil museum.
The first attempt to manufacture graphite sticks from powdered graphite was in Nuremberg, Germany, in 1662.
It used a mixture of graphite, sulphur, and antimony.
Wood holders added
The Italians first thought of wooden holders.
In 1560, an Italian couple named Simonio and Lyndiana Bernacotti created the first blueprints for the modern carpentry pencil to mark their carpentry pieces.
Their version was instead a flat, oval, more compact type of pencil.
They did this at first by hollowing out a stick of juniper wood.
Shortly thereafter, a superior technique was discovered: two wooden halves were carved, a graphite stick inserted, and the two halves then glued together–essentially the same method in use to this day.
English and German pencils were not available to the French during the Napoleonic Wars.
France was under naval blockade imposed by Great Britain and could not import the pure graphite sticks from the British Grey Knotts mines – the only known source in the world for solid graphite.
In 1795, Nicholas Jacques Conté discovered a method of mixing powdered graphite with clay and forming the mixture into rods that were then fired in a kiln.
By varying the ratio of graphite to clay, the hardness of the graphite rod could also be varied.
This method of manufacture, which had been earlier discovered by the Austrian Joseph Hardtmuth of Koh-I-Noor in 1790, remains in use.
In England, pencils continued to be made from whole sawn graphite.
Henry Bessemer's first successful invention (1838) was a method of compressing graphite powder into solid graphite thus allowing the waste from sawing to be reused.
American colonists imported pencils from Europe until after the American Revolution.
Benjamin Franklin advertised pencils for sale in his Pennsylvania Gazette in 1729, and George Washington used a three-inch pencil when he surveyed the Ohio Territory in 1762.
It is said that William Munroe, a cabinetmaker in Concord, Massachusetts, made the first American wood pencils in 1812.
This was not the only pencil-making occurring in Concord.
Henry David Thoreau discovered how to make a good pencil out of inferior graphite using clay as the binder; this invention was prompted by his father's pencil factory in Concord, which employed graphite found in New Hampshire in 1821 by Charles Dunbar.
Eraser attached
On 30 March 1858, Hymen Lipman received the first patent for attaching an eraser to the end of a pencil.
In 1862 Lipman sold his patent to Joseph Reckendorfer for $100,000, who went to sue the pencil manufacturer Faber-Castell for infringement.
In 1875, the Supreme Court of the United States ruled against Reckendorfer declaring the patent invalid.
The first attempt to manufacture graphite sticks from powdered graphite was in Nuremberg, Germany in 1662.
They used a mixture of graphite, sulfur and antimony.
Though usable, they were not as good as the English pencils.
English and German pencils were not available to the French during the Napoleonic wars.
In 1795 Nicholas Jacques Conté discovered a method of mixing powdered graphite with clay and forming the mixture into rods which were then fired in a kiln.
By varying the ratio of graphite to clay, the hardness of the graphite rod could also be varied (the more clay, the harder the pencil, and the lighter the color of the mark).
This method of making pencils is still used today.
Modern day pencils
Today, pencils are made industrially by mixing finely ground graphite and clay powders, adding water, forming long spaghetti-like strings, and firing them in a kiln.
The resulting strings are dipped in oil or molten wax which seeps into the tiny holes of the material, resulting in smoother writing.
A juniper or incense-cedar plank with several long parallel grooves is cut to make something called a slate, and the graphite/clay strings are inserted into the grooves.
Another grooved plank is glued on top, and the whole thing is then cut into individual pencils, which are then varnished or painted.
Logic is the study of reasoning.
The rules of logic let philosophers make valid logical deductions about the world.
Logic helps people decide whether something is true or false.
Logic is often written in syllogisms, which are one type of logical proof.
A syllogism is made from a collection of statements used to logically prove the final statement, called the conclusion.
One popular example of a logical syllogism was written by the Classical Greek philosopher Aristotle:
The conclusion is the final statement.
This syllogism connects the first two statements to make a logical deduction: Socrates is mortal.
The syllogism is made from three logical statements or propositions.
These statements are short sentences describing a small step in a logical argument.
The small statements make up the argument, the same way atoms make up molecules.
When logic is correct, the statements are said to "follow" from each other.
Statements have a truth value, meaning they can be proved to be true or false, but not both.
Illogical statements or mistakes in logic are called logical fallacies.
Symbolic logic
Logical statements can be written in a special type of short hand writing, which includes the symbols of the symbolic logic.
These symbols are used to describe logical reasoning in an abstract way.
is read like "and", meaning both statements apply.
is read like "or", meaning at least one of the statements applies.
is read like "implies", "are," or "If ... then ...".
It represents the result of a logical statement.
is read like "not", or "it is not the case that ...".
is read like "therefore", which is used to mark the conclusion a logical argument.
is read like "parentheses".
They group logical statements together.
Statements in parentheses should always be considered first, following the order of logical operations.
Similar to mathematical symbols for operations like addition and subtraction, symbolic logic separates abstract logic from the English-language meaning of the original statements.
With these abstract symbols, people can study pure logic without the use of a specific written language.
The syllogism is now written in the most abstract and simple way possible.
Any distracting elements, such as English language words, have been removed.
Anyone who understands logical symbolism can understand this argument.
Logical proof
A logical proof is a list of statements put in a specific order to prove a logical point.
Each statement in the proof is either an assumption made for the sake of argument, or has been proven to follow from earlier statements in the proof.
All proofs must start with some assumptions, such as "humans exist" in the above syllogism.
A proof shows that one statement, the conclusion, follows from the starting assumptions.
With a proof, we can prove that "Aristotle is mortal" logically follows from "Aristotle is a man" and "All men are mortal".
Some statements are always true.
That kind of statement is called tautology.
One popular classical tautology, credited to the philosopher Parmenides of Elea, says "That which is, is.
That which is not, is not."
This essentially means that true statements are true and false statements are false.
Due to their simple nature, tautologies may not always be helpful in building logical arguments.
A tautology is represented in symbolic logic as , meaning "Either a or not a." Assuming that there are no unmentioned possibilities, this covers every possible case.
Another symbol used to represent a tautology is .
Because logic is a tool used to think more rationally, it can be used in countless ways.
Symbolic logic is employed far and wide, from philosophical treatises to complicated mathematical equations.
Computers use the rules of logic to run algorithms, which let computer programs make decisions based on data.
Logic is critical to pure mathematics, statistics, and data analysis.
Logic is also studied in philosophy.
People who study math create proofs that use logical rules to show that mathematical theorems are correct.
There is an area of mathematics called mathematical logic that studies logic using mathematics.
Communism is a socio-economic political ideology and movement.
It strives to set up a society where there are no states and where there is no money.
Additionally, it wants the means of production (like factories, tools and farms) to be in the hands of the people (which is the definition of socialism).
This is the opposite to capitalism where there is money, a state and class.
In capitalism, there is a working class (people who don't own the means of production) and the capitalist class (people who own the means of production).
Communist thinkers believe this can happen if the working class take away the power of the bourgeoisie (the capitalist class, sometimes called the ruling class) and establish worker control of the means of production.
There are now only 5 communist countries.
Four of these follow different forms of Marxism-Leninism (a theory of communism and Marxism) - Vietnam, China, Cuba and Laos.
The fifth, North Korea, now officially follows Juche (which is a variant of Marxism).