adityasasidhar/Wikipedia_Cleaned huggingface dataset:
The multiplicative inverse property means that when we multiply a number and its reciprocal, the result is 1. Algebraically, it states the following: formula_106, which is the same as formula_107. For example, the multiplicative inverse (or reciprocal) of 2 is 1/2. To get the reciprocal of a fraction, switch the numerator and the denominator: the reciprocal of formula_108 is formula_109.
In addition to "elementary algebra", or basic algebra, there are advanced forms of algebra, taught in colleges and universities, such as abstract algebra, linear algebra, and universal algebra. This includes how to use a matrix to solve many linear equations at once. Abstract algebra is the study of things that are found in equations, going beyond numbers to the more abstract with groups of numbers.
Many math problems are about physics and engineering. In many of these physics problems time is a variable. The letter used for time is formula_110. Using the basic ideas in algebra can help reduce a math problem to its simplest form making it easier to solve difficult problems. Energy is formula_54, force is formula_112, mass is formula_60, acceleration is formula_82 and speed of light is sometimes formula_115. This is used in some famous equations, like formula_116 and formula_117 (although more complex math beyond algebra was needed to come up with that last equation).
Atoms are very small, but their exact size depends on the type. Atoms are from 0.1 to 0.5 nanometers across. One nanometer is about 100,000 times smaller than the width of a human hair. This makes one atom impossible to see without special tools. Scientists learn how they work by doing experiments.
Atoms are made of three kinds of subatomic particles. These are protons, neutrons, and electrons. Protons and neutrons have much more mass. These are in the middle of the atom, called the nucleus. Lightweight electrons move quickly around them. The electromagnetic force holds the nucleus and electrons together.
Atoms with the same number of protons belong to the same chemical element. Examples of elements are carbon and gold. Atoms with the same number of protons, but different numbers of neutrons, are called isotopes. Usually an atom has the same number of electrons as protons. If an atom has more or less electrons than protons, it is called an ion, and has an electric charge.
Atoms can join by chemical bonds. Many things are made of more than one kind of atom. These are chemical compounds or mixtures. A group of atoms connected by chemical bonds is called a molecule. For example, a water molecule is made of two hydrogen atoms and one oxygen atom. The forming or breaking of bonds is a chemical reaction.
Atoms split if the forces inside are too weak to hold them together. This is what causes radioactivity. Atoms can also join to make larger atoms at very high temperatures, such as inside a star. These changes are studied in nuclear physics. Most atoms on Earth are not radioactive. They are rarely made, destroyed, or changed into another kind of atom.
In 1777 French chemist Antoine Lavoisier defined the term "element" as we now use it. He said that an element was any substance that could not be broken down into other substances by the methods of chemistry. Any substance which could be broken down was a "compound".
In 1803, English philosopher John Dalton suggested that elements were made of tiny, solid balls called atoms. Dalton believed that all atoms of the same element have the same mass. He said that compounds are formed when atoms of more than one element combine. In any one compound, the atoms would always combine in the same numbers.
In 1827, British scientist Robert Brown looked at pollen grains in water under his microscope. The pollen grains appeared to be shaking. Brown used Dalton's atomic theory to describe patterns in how they moved. This was called "Brownian motion". In 1905 Albert Einstein used mathematics to prove that the pollen particles were being moved by the motion, or heat, of individual water molecules. By doing this, he proved that atoms are real without question.
In 1869, Russian scientist Dmitri Mendeleev published the first periodic table. The periodic table groups elements by their atomic number (how many protons they have; this is usually the same as the number of electrons). Elements in the same column, or group, usually have similar qualities. For example, helium, neon, argon, krypton, and xenon are all in the same column and are very similar. All these elements are gases that have no color or smell. Also, they cannot combine with other atoms to form compounds. Together they are known as noble gases.
The physicist J.J. Thomson was the first person to discover electrons. This happened while he was working with cathode rays in 1897. He learned they had a negative charge, and the rest of the atom had a positive charge. Thomson made the plum pudding model, which said that an atom was like plum pudding: the dried fruit (electrons) were stuck in a mass of pudding (having a positive charge).
In 1913, Niels Bohr created the Bohr model. This model showed that electrons travel around the nucleus in fixed circular orbits. This was better than the Rutherford model, but it was still not completely true.
In 1925, chemist Frederick Soddy discovered that some elements had more than one kind of atom, called isotopes. Soddy believed that each different isotope of an element has a different mass. To prove this, chemist Francis William Aston built the mass spectrometer, which measures the mass of single atoms. Aston proved that Soddy was right. He also found that the mass of each atom is a whole number times the mass of the proton. This meant that there must be some particles in the nucleus other than protons. In 1932, physicist James Chadwick shot alpha particles at beryllium atoms. He saw that a particle shot out of the beryllium atoms. This particle had no charge, but about the same mass as a proton. He named this particle the neutron.
In 1937, German chemist Otto Hahn became the first person to make nuclear fission in a laboratory. He discovered this by chance when shooting neutrons at a uranium atom, hoping to make a new isotope. However, instead of a new isotope, the uranium changed into a barium atom, a smaller atom than uranium. Hahn had "broken" the uranium atom. This was the world's first recorded nuclear fission reaction. This discovery led to the creation of the atomic bomb and nuclear power, where fission happens over and over again, creating a chain reaction.
Later in the 20th century, physicists went deeper into the mysteries of the atom. Using particle accelerators, they discovered that protons and neutrons were made of other particles, called quarks.
An atom is made of three main particles: the proton, the neutron, and the electron. Protons and neutrons have nearly the same size and mass (about grams). The mass of an electron is about 1800 times smaller (about grams). Protons have a positive charge, electrons have a negative charge, and neutrons have no charge. Most atoms have no charge. The number of protons (positive) and electrons (negative) are the same, so the charges balance out to zero. However, ions have a different number of electrons than protons, so they have a positive or negative charge.
Scientists believe that electrons are elementary particles: they are not made of any smaller pieces. Protons and neutrons are made of quarks of two kinds: up quarks and down quarks. A proton is made of two up quarks and one down quark, and a neutron is made of two down quarks and one up quark.
The nucleus is in the middle of the atom. It is made of protons and neutrons. The nucleus makes up more than 99.9% of the mass of the atom. However, it is very small: about 1 femtometer (10 m) across, which is around 100,000 times smaller than the width of an atom, so it has a very high density.
Usually in nature, two things with the same charge repel or shoot away from each other. So for a long time, scientists did not know how the positively charged protons in the nucleus stayed together. We now believe that the attraction between protons and neutrons comes from the "strong nuclear force". This force also holds together the quarks that make up the protons and neutrons. Particles called mesons travel back and forth between protons and neutrons, and carry the force.
The number of neutrons in relation to protons defines whether the nucleus stays together or goes through radioactive decay. When there are too many neutrons or protons, the atom tries to make the numbers smaller or more equal by removing the extra particles. It sends out radiation in the form of alpha, beta, or gamma decay. Nuclei can also change in other ways. Nuclear fission is when the nucleus breaks into two smaller nuclei, releasing a lot of energy. This release of energy makes nuclear fission useful for making bombs, and electricity in the form of nuclear power.
The other way nuclei can change is through nuclear fusion, when two nuclei join or fuse to make a larger nucleus. This process requires very high amounts of energy to overcome the electric repulsion between the protons, as they have the same charge. Such high energies are most common in stars like our Sun, which fuses hydrogen for fuel. However, once fusion happens, far more energy is released, because some of the mass becomes energy.
The energy needed to break a nucleus into protons and neutrons is called its nuclear binding energy. This energy can be converted to mass, as stated by Einstein's famous formula "E" = "mc". Medium-sized nuclei, such as iron-56 and nickel-62, have the highest binding energy per proton or neutron. They will probably not go through fission or fusion, because they cannot release energy in this way. Very small and very large atoms have low binding energy, so they are most willing to go through fission or fusion.
Electrons orbit, or travel around, the nucleus. They are called the atom's "electron cloud". They are attracted to the nucleus because of the electromagnetic force. Electrons have a negative charge, and the nucleus always has a positive charge, so they attract each other.
The Bohr model shows that some electrons are farther from the nucleus than others in different levels. These are called "electron shells". Only the electrons in the outer shell can make chemical bonds. The number of electrons in the outer shell determines whether the atom is stable or which atoms it will bond with in a chemical reaction. If an atom has only one shell, it needs two electrons to be complete. Otherwise, the outer shell needs eight electrons to be complete.
The Bohr model is important because it has the idea of energy levels. The electrons in each shell have a certain amount of energy. Shells that are farther from the nucleus have more energy. When a small burst of energy called a photon hits an electron, the electron can jump into a "higher-energy" shell. This photon must carry exactly the right amount of energy to bring the electron to the new energy level. A photon is a burst of light, and the amount of energy determines the color of light. So each kind of atom will absorb certain colors of light, called the absorption spectrum. An electron can also send out, or emit, a photon, and fall into a "lower energy" shell. For the same reason, the atom will only send out certain colors of light, called the emission spectrum.
The complete picture is more complicated. Unlike the Earth moving around the Sun, electrons do not move in a circle. We cannot know the exact place of an electron. We only know the probability, or chance, that it will be in any place. Each electron is part of an "orbital", which describes where it is likely to be. No more than two electrons can be in one orbital; these two electrons have different "spin".
For each shell, numbered 1, 2, 3, and so on, there may be a number of different orbitals. These have different shapes, or point in different directions. Each orbital can be described by its three "quantum numbers". The "principal quantum number" is the electron shell number. The "azimuthal quantum number" is represented by a letter: s, p, d, or f. Depending on the principal and azimuthal quantum numbers, the electron can have more or less energy. There is also a "magnetic quantum number", but it does not usually affect the energy level. As more electrons are added, they join orbitals in order from lowest to highest energy. This order starts as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d. For example, a chlorine atom has 17 electrons. So, it will have:
In other words, it has 2 electrons in the first shell, 8 in the second shell, and 7 in the third shell.
The number of protons in an atom is called its "atomic number". Atoms of the same element have the same atomic number. For example, all carbon atoms have six protons, so the atomic number of carbon is six. Today, 118 elements are known. Depending on how the number is counted, 90 to 94 elements exist naturally on earth. All elements above number 94 have only been made by humans. These elements are organized on the periodic table.
Because protons and neutrons have nearly the same mass, and the mass of electrons is very small, we can call the number of protons and neutrons in an atom its "mass number". Most elements have several isotopes with different mass numbers. To name an isotope, we use the name of the element, followed by its mass number. So an atom with six protons and seven neutrons is called carbon-13.
Sometimes, we need a more exact measurement. The exact mass of an atom is called its "atomic mass". This is usually measured with the atomic mass unit (amu), also called the dalton. One amu is exactly 1/12 of the mass of a carbon-12 atom, which is grams. Hydrogen-1 has a mass of about 1 amu. The heaviest atom known, oganesson, has a mass of about 294 amu, or grams. The average mass of all atoms of a particular element is called its "atomic weight".
The size of an atom depends on the size of its electron cloud. Moving down the periodic table, more electron shells are added. As a result, atoms get bigger. Moving to the right on the periodic table, more protons are added to the nucleus. This more positive nucleus pulls electrons more strongly, so atoms get smaller. The biggest atom is caesium, which is about 0.596 nanometers wide according to one model. The smallest atom is helium, which is about 0.062 nanometers wide.
When atoms are far apart, they attract each other. This attraction is stronger for some kinds of atoms than others. At the same time, the heat, or kinetic energy, of atoms makes them always move. If the attraction is strong enough, relative to the amount of heat, atoms will form a solid. If the attraction is weaker, they will form a liquid, and if it is even weaker, they will form a gas.
Chemical bonds are the strongest kinds of attraction between atoms. The movement of electrons explains all chemical bonds.
Atoms usually bond with each other in a way that fills or empties their outer electron shell. The most reactive elements have an almost full or almost empty outer shell. Atoms with a full outer shell, called noble gases, do not usually form bonds.
There are three main kinds of bonds: ionic bonds, covalent bonds, and metallic bonds.
All atoms attract each other by Van der Waals forces. These forces are weaker than chemical bonds. They are caused when electrons move to one side of an atom. This movement gives a negative charge to that side. It also gives a positive charge to the other side. When two atoms line up their sides with negative and positive charges, they will attract.
Although atoms are mostly empty space, they cannot pass through each other. When two atoms are very close, their electron clouds will repel each other by the electromagnetic force.
To understand how magnets work, we can look at the properties of the atom. Any magnet has a north and south pole, and a certain strength. The direction and strength of a magnet, together, are called its magnetic moment. Every electron also has a magnetic moment, like a tiny magnet. This comes from the electron's spin and its orbit around the nucleus. The magnetic moments for the electrons add up to a magnetic moment for the whole atom. This tells us how atoms act in a magnetic field.
Every electron has one of two opposite spins. We can think of one as turning to the right, and the other as turning to the left. If every electron is paired with an electron with the opposite spin in the same orbital, the magnetic moments will cancel out to zero. Atoms like this are called diamagnetic. They are only weakly repelled by a magnetic field.
However, if some electrons are not paired, the atom will have a lasting magnetic moment: it will be paramagnetic or ferromagnetic. When atoms are paramagnetic, the magnetic moment of each atom points in a random direction. They are weakly attracted to a magnetic field. When atoms are ferromagnetic, the magnetic moments of nearby atoms act on each other. They point in the same direction. This means that the whole object is a magnet, and it can point in the direction of a magnetic field. Ferromagnetic materials, such as iron, cobalt, and nickel, are strongly attracted to a magnetic field.
Some elements, and many isotopes, have what is called an "unstable nucleus". This means the nucleus is either too big to hold itself together, or it has too many protons or neutrons. When a nucleus is unstable, it has to eliminate the excess mass of particles. It does this through radiation. An atom that does this is called "radioactive". Unstable atoms emit radiation until they lose enough particles in the nucleus to become stable. All atoms above atomic number 82 (82 protons, lead) are radioactive.
There are three main kinds of radioactive decay: alpha, beta, and gamma.
Every radioactive element or isotope has a "half-life". This is how long it takes half of any sample of atoms of that type to decay into a different isotope or element.
Nearly all the hydrogen atoms in the Universe, most of the helium atoms, and some of the lithium atoms were made soon after the Big Bang. Even today, about 90% of all atoms in the Universe are hydrogen.
All other atoms come from nuclear fusion in stars, or sometimes from cosmic rays that hit atoms. At the start of their life, all stars fuse hydrogen to make helium. The least massive stars, red dwarfs, are expected to stop there. All other stars will then fuse helium to make carbon and oxygen. In stars like the Sun, the temperature and pressure are too low to make larger atoms. But more massive stars continue fusion, until they create iron (atomic number 26) or nickel (atomic number 28). Atoms can also grow larger when neutrons or protons hit them. This could happen inside stars or in supernovae. Most atoms on Earth were made by a star that existed before the Sun.
People make very large atoms by smashing together smaller atoms in particle accelerators. However, these atoms often decay very quickly. Oganesson (element 118) has a half-life of 0.00089 seconds. Even larger atoms may be created in the future.
Astronomy is the scientific study of celestial bodies. Stars, galaxies, planets, moons, asteroids, comets and nebulae are studied, as are supernovae explosions, gamma ray bursts, and cosmic microwave background radiation. Astronomy includes the development, physics, chemistry, meteorology and movement of celestial bodies. The big questions are the structure and development of the universe.
Astronomy is one of the oldest sciences. The patterns in the night sky were called constellations by the Arabs. They used the positions of the stars to navigate, and to find when was the best time to plant crops.
Astrophysics is an important part of astronomy. A related subject, cosmology, is concerned with studying the universe as a whole, and the way the universe changed over time. Astronomy is not the same as "astrology", a belief that the motion of the stars and the planets may affect human lives.
There are two main types of astronomy, "observational" and "theoretical" astronomy. Observational astronomy uses telescopes and cameras to "observe" or look at stars, galaxies and other astronomical objects. Theoretical astronomy explains what we see. It predicts what might happen. Observations show whether the predictions work. The main work of astronomy is to explain puzzling features of the universe. For many years the most important issue was the motions of planets. Many other topics are now studied.
Day-time astronomy is possible. First, there's the Sun, but observing directly is dangerous. It is too bright, and can burn your eyes and can cause permanent blindness. To look at the Sun you need proper shields and equipment. Some other individual bright stars and planets can be seen during daylight hours through a telescope or a powerful pair of binoculars.
Ancient Greeks tried to explain the motions of the sun and stars by taking measurements. A mathematician named Eratosthenes was the first who measured the size of the Earth and proved that the Earth is a sphere. A theory by another mathematician named Aristarchus was, that the sun is the center and the Earth is moving around it. This is known as heliocentrism. Only a few people thought it was right. The rest continued to believe in the "geocentric" model. Most of the names of constellations and stars come from Greeks of that time.
During the renaissance a priest named Nicolaus Copernicus thought, from looking at the way the planets moved, that the Earth was not the center of everything. Based on previous works, he said that the Earth was a planet and all the planets moved around the sun. This brought back the old idea of heliocentrism. Galileo Galilei built his own telescopes, and used them to look more closely at the stars and planets for the first time. He agreed with Copernicus. The Catholic Church thought Galileo was wrong. He spent the rest of his life under house arrest. Heliocentric ideas were soon improved by Johannes Kepler and Isaac Newton, who invented the theory of gravity.
The opening of this new window on the Universe saw the discovery of entirely new things, for example pulsars, which sent regular pulses of radio waves out into space. The waves were first thought to be alien in origin because the pulses were so regular that (so it was thought) it implied an artificial source.
The period after World War II saw more observatories. Large and accurate telescopes were built and operated at good observing sites, usually by governments. For example, Bernard Lovell began radio astronomy at Jodrell Bank using leftover military radar equipment. By 1957, the site had the largest steerable radio telescope in the world. Similarly, the end of the 1960s saw the start of the building of dedicated observatories at Mauna Kea in Hawaii, a good site for visible and infra-red telescopes thanks to its high altitude and clear skies.
Noise phenomena tend to relate to things that happened a long time ago. The signal from these events bounce around the Universe until it seems to come from everywhere and varies little in intensity. In this way, it is "noise", the background signal that pervades every instrument used for astronomy. The most common example of noise is static seen on analogue televisions. The principal astronomical example is: cosmic background radiation.
Data analysis is the process of getting more information out of an astronomical observation than by simply looking at it. The observation is first stored as data. This data then has various techniques used to analyse it.
Solar astronomy is the study of the Sun. The Sun is the closest star to Earth at around 92 million (92,000,000) miles away. It is the easiest to observe in detail. Observing the Sun can help us understand how other stars work and are formed. Changes in the Sun can affect the weather and climate on Earth. A stream of charged particles called the Solar wind is constantly sent off from the Sun. The Solar wind hitting the Earth's magnetic field causes the northern lights.
Stellar Astronomy
Planetary astronomy is the study of planets, moons, dwarf planets, comets and asteroids as well as other small objects that orbit stars. The planets of our own Solar System have been studied in depth by many visiting spacecraft such as Cassini-Huygens (Saturn) and the Voyager 1 and 2.
Galactic astronomy is the study of distant galaxies. Studying distant galaxies is a good way of learning about our own galaxy, as the gases and stars in our own galaxy make it difficult to observe. Galactic astronomers try to understand the structure of galaxies and how they are formed by using different types of telescopes and computer simulations.
Gravitational wave astronomy is the study of the Universe in the gravitational wave spectrum. So far, all astronomy that has been done has used the electromagnetic spectrum. Gravitational waves are ripples in spacetime emitted by very dense objects changing shape, which include white dwarves, neutron stars and black holes. Because no one has been able to detect gravitational waves directly, the impact of gravitational wave astronomy has been limited.
Great discoveries also produce unsolved problems. This is just a short-list:
Architecture is the process of designing structures and buildings. It uses both art and engineering. Examples include houses, churches, hotels, office buildings, roads, tunnels and bridges.
Academic human anatomists are usually employed by universities, medical schools and teaching hospitals. They are often involved in teaching and research. Gross anatomy studies parts of the body that are big enough to see. Micro-anatomy studies smaller parts.
An asteroid is a minor planet that orbits within the inner solar system. It is a small object in the Solar System that travels around the Sun. It is like a planet but smaller. They range from very small (smaller than a car) to 600 miles (1000 km) across. A few asteroids have asteroid moon.
The name "asteroid" means "like a star" in the ancient Greek language. Asteroids may look like small stars in the sky, but they really do move around the Sun. Like planets, asteroids do not make their own light. Because of this, some people think "asteroids" is not a good name, and think that the name "planetoid" ("like a planet") would be a better name.
Giuseppe Piazzi found the first asteroid, in 1801. He called it Ceres, and it is the biggest object in the asteroid belt. Others, like Juno, Pallas, and Vesta were found later. In the 1850s, so many had been found that they were numbered by a Minor planet designation starting with 1 Ceres. Today, astronomers using computerized telescopes find thousands of asteroids every month. Asteroid impact prediction is one of their purposes.
Most asteroids in our Solar System are in the asteroid belt between Mars and Jupiter. Many are not in the main asteroid belt. The ones that come close to Earth are called Near-Earth asteroids. Some scientists think asteroids striking the Earth killed off all the dinosaurs and caused some of the other extinction events.
Afghanistan, officially the Islamic Emirate of Afghanistan is a country in Asia. It borders Pakistan in the south and east, Iran in the west, Turkmenistan, Uzbekistan and Tajikistan in the north, and China in the far northeast. Kabul is the capital city.
Afghanistan is currently governed by the Taliban, after the collapse of the internationally recognized Islamic Republic of Afghanistan on 15 August 2021. In early times people passed through it with animals and other goods as it connected China and India with Central Asia and the Middle East. More recently, Afghanistan has been damaged by many years of war. There are not enough jobs.
The country is around in size. There are 40.976 million people in Afghanistan. There are about 3 million Afghan refugees (people who had to leave the country) in Pakistan and Iran. In 2011 Kabul, had about 3,691,400 people living in it.
United Nations Human Rights Council decided in October 2021 to appoint (an independent expert, or) United Nations special rapporteur on "Afghanistan to [find out about, or] probe violations carried out by the Taliban and" others who are now part of a [big] conflict.
Afghanistan has many mountains. The mountains are called the Hindu Kush and Himalayas. The tallest mountain in Afghanistan is Mount Nowshak. There are plains (which have soil that is good for growing plants) and foothills. Parts of the country are also dry, especially the Registan Desert. Afghanistan has snow and glaciers in the mountains. Amu Darya is the big water stream, or river.
The country has a lot of a valuable stone called lapis lazuli, which was used to decorate the tomb of the Egyptian pharaoh Tutankhamun.
Many people have moved through or invaded the land of Afghanistan. Today's people of Afghanistan are known as "Afghans".
The largest group of people are the Pashtuns. These make up about half the population. Tajiks are the second-largest ethnic group, making up about one-fifth of the population. Before the 20th century, Tajiks were called Sarts and some come from Iranian peoples. Most Pashtuns are also related to the Iranian peoples. Some Pashtuns and Tajiks marry each other but at the same time they are rivals. The third-largest group are the Hazaras. They are native to the Hazaristan area in central Afghanistan. The country's other groups include the Uzbek, Aimaq, Turkmen, Nuristani, Baloch, and Pashayi.
Dari-Persian and Pashto are the official languages of Afghanistan. Many people speak both languages. Both are Indo-European languages from the Iranian languages sub-family. They are usually written with the Arabic alphabet. Uzbek and Turkmen are widely spoken in the north and Nuristani and Pashai are spoken in the east. Around 99% of Afghans follow the religion of Islam.
Afghanistan is a largely rural country. This means there are only a few major cities. About one fifth of the population live in cities. Kabul, the capital, is the largest city. It is south of the Hindu Kush range and alongside the Kabul River. Other cities are Kandahar, Herat, Mazar-e Sharif, and Jalalabad. The rural population is made up of farmers and nomads. The farmers live mainly in small villages along the rivers. The nomads live in tents while moving from place to place with their animals and belongings. Some people live in the high central mountains. Some live in the deserts in the south and southwest. Millions of people left Afghanistan to get away from the wars that happened in the late 20th and early 21st centuries. Most of them went to Pakistan and Iran.
Afghanistan is in the path of important trade routes that connect southern and eastern Asia to Europe and the Middle East. Because of this, many empire builders have tried to rule over the area. Signs that these emperors were near Afghanistan still exist in many parts of the country. Afghanistan is near what used to be the Silk Road. The peoples of Afghanistan helped develop major world religions, traded and exchanged many products, and sometimes controlled politics and culture in Asia.
The Oxus civilization expanded as far east as western edge of the Indus Valley during the period between 2200 and 1800 B.C. These people, who were the ancestors of the Indo-Aryans, used the term "Aryan" to identify their ethnicity, culture, and religion. Scholars know this when they read the ancient texts of these people; the Avesta of Iranic peoples and the Vedas of Indo-Aryans.
Before the middle of the sixth century BCE, Afghanistan was held by the Medes. Then the Achaemenids took over control of the land and made it part of the Persian empire. Alexander the great defeated and conquered the Persian Empire in 330 BCE. He founded some cities in the area. The people used Macedonian culture and language. After Alexander, Greco-Bactrians, Scythians, Kushans, Parthians and Sassanians ruled the area.
In the 10th century, the local Ghaznavids turned Ghazni into their capital and firmly established Islam throughout all areas of Afghanistan, except the Kafiristan region in the northeast. Mahmud of Ghazni, a great Ghaznavid sultan, conquered the Multan and Punjab region, and carried raids into the heart of India. Mohammed bin Abdul Jabbar Utbi, a historian from the 10th century, wrote that thousands of "Afghans" were in the Ghaznavid army. The Ghaznavid dynasty was replaced by the Ghorids of Ghor in the late 12th century, who reconquered Ghaznavid territory in the name of Islam and ruled it until 1206. The Ghorid army also included ethnic Afghans.
Between south of the Hindu Kush and the Indus River (today's Pakistan) was the native land of the Afghan tribes. They called this land "Afghanistan" (meaning "land of the Afghans"). The Afghans ruled the rich northern Indian subcontinent with their capital at Delhi. From the 16th to the early 18th century, Afghanistan was disputed between the Safavids of Isfahan and the Mughals of Agra who had replaced the Lodi and Suri Afghan rulers in India. The Safavids and Mughals occasionally oppressed the native Afghans but at the same time the Afghans used each empire to punish the other. In 1709, the Hotaki Afghans rose to power and completely defeated the Persian Empire. Then they marched towards the Mughals of India and defeated them with the help of the Afsharid forces under Nader Shah Afshar.
During the 1800s, Afghanistan became a buffer zone between two powerful empires, the British Indian Empire and the Russian Empire. As British India advanced into Afghanistan, Russia felt threatened and expanded southward across Central Asia. To stop the Russian advance, Britain tried to make Afghanistan part of its empire but the Afghans fought wars with British-led Indians from 1839 to 1842 and from 1878 to 1880. After the third war in 1919, Afghanistan under King Amanullah gained respect and recognition as a completely independent state.
Most people in Afghanistan opposed the sudden Soviet presence in their country. For nearly a decade, anti-Communist Islamic forces known as "Mujahideen" were trained in Pakistan to fight the Soviets and the Afghan government. The United States and other anti-Soviet countries supported the Mujahideen. In the long war, over one million Afghan civilians were killed. The Soviet Army also lost more than 15,000 soldiers in that war. Millions of Afghans left their country to stay safe in neighboring Pakistan and Iran. In 1989 the Soviet Army withdrew the last of its troops.
After the Soviets left in 1989, the Afghan Civil War started; different Afghan warlords began fighting for control of the country. The warlords received support from other countries, including neighboring Pakistan and Iran. A very conservative Islamic group known as the Taliban emerged in an attempt to end the civil war. By the late 1990s the Taliban had gained control over 95% of Afghanistan. A group known as the Northern Alliance, based in northern Afghanistan near the border with Tajikistan, continued to fight against the Taliban.
The Taliban ruled Afghanistan according to their strict version of Islamic law. People whom the Taliban believed violated these laws were given cruel punishments. In addition, the Taliban completely restricted the rights of women. Because of such policies, most countries refused to recognize the Taliban government. Only Pakistan, Saudi Arabia and the United Arab Emirates accepted them as the official government. The Taliban also angered other countries by allowing suspected terrorists to live freely in Afghanistan. Among them were Osama bin Laden and members of the al-Qaeda terrorist network. In September 2001, the United States blamed bin Laden for the terrorist attacks on the World Trade Center in New York City and the Pentagon outside Washington, D.C. The Taliban refused to hand him over to the United States. In response, the United States and its allies launched a bombing campaign against al-Qaeda in October 2001. Within months the Taliban abandoned Kabul, and a new government led by Hamid Karzai came to power, but fighting between the Taliban and US-led armies continued. Taliban fighters have gone into Afghanistan from neighboring Pakistan. Afghans accused Pakistan's military of being behind the Taliban militants but Pakistan rejected this and stated that a stable Afghanistan is in Pakistan's own interest.
In December 2004, Hamid Karzai became the first democratically elected president of Afghanistan. NATO began rebuilding Afghanistan, including its military and government institutions. Many schools and colleges were built. Freedom for women improved. Women can study, work, drive, and run for office. Many Afghan women work as politicians, some are ministers while at least one is a mayor. Others have opened businesses, or joined the military or police. Afghanistan's economy has also improved dramatically, and NATO agreed in 2012 to help the country for at least another 10 years after 2014. Afghanistan improved diplomatic ties with many countries in the world and continues.
In August 2021, the Cabinet of Afghanistan lost its power. Most of the country fell to the Taliban on 15 August 2021 with President Ashraf Ghani escaping the country. As of 18 August 2021, the former government's last remaining holdout is the Panjshir Valley.
Angola, officially the Republic of Angola, is a country in southern Africa. It shares borders with Namibia in the south, the Democratic Republic of the Congo in the north, and Zambia in the east. Its west border touches the Atlantic Ocean. Its coastline is 1600 kilometers. Angola's capital is Luanda. The country has many natural resources. Angola is the seventh largest country in Africa. The capital and most populated city of Angola is Luanda.
After independence there was a civil war from 1975 to 2002. Cuba and the Soviet Bloc supported the ruling People's Movement for the Liberation of Angola (MPLA). South Africa supported the insurgent National Union for the Total Independence of Angola (UNITA) until the end of apartheid. The war ended after the rebel leader Jonas Savimbi was killed.
Angola is the world's twenty-third largest country. Angola is bordered by Namibia to the south, Zambia to the east, the Democratic Republic of the Congo to the north-east, the Republic of the Congo via the exclave of Cabinda, and the South Atlantic Ocean to the west.
Argentina is a federal republic. The people of Argentina vote for a President to rule them and Senators and Deputies to speak for them and make laws for them. The President is Javier Milei since December 2023.
Argentina is almost 3,700 km long from north to south, and 1,400 km from east to west (maximum values). It can be divided into three parts: the Pampas in the central part of the country, Patagonia in the southern part down to Tierra del Fuego; and the Andes mountain range along the western border with Chile, with the highest point in the province of Mendoza. Cerro Aconcagua, at 6,960 metres (22,834 ft), is the Americas' highest mountain.
The majority of the Argentineans are descendants of Europeans mainly from Spain, Italy, Russia, France, Germany , Arabs other Europeans countries and Mestizo representing more than 90% of the total population of the country. More than 300,000 Roma gypsies live in Argentina. Since the 1990s, Romanian, Brazilian and Colombian gypsies arrived in Argentina.
Austria (, ; ), officially the Republic of Austria ( ), is a country in Central Europe. Around Austria there are the countries of Germany, Czech Republic, Slovakia, Hungary, Slovenia, Italy, Switzerland, and Liechtenstein.
The people in Austria speak German, a few also speak Hungarian, Slovenian and Croatian. The capital of Austria is Vienna ("Wien").
From the early Middle Ages, the area of modern-day Austria was a part of the Holy Roman Empire. The capital of the Holy Roman Empire was the Austrian city Vienna. The Austrian Habsburg family were the rulers of the Empire and the son of the Holy Roman Emperor held the title of Archduke of Austria.
In 1806, France defeated the Holy Roman Empire and replaced it with the Confederation of the Rhine. Former Holy Roman Emperor Francis II became the Emperor of the new Austrian Empire, which later became Austria-Hungary.
In 1914, Franz Ferdinand was assassinated in Sarajevo. Austria-Hungary declared war on Serbia and this led to World War I. In 1918, both Austria and Hungary became republics. They also both split into two separate countries.
During World War II, Austria was part of Nazi Germany. It became independent in May 1945.
Austria is a mountainous country since it is partially in the Alps. Grossglockner is the tallest mountain in Austria. The high mountainous Alps in the west of Austria flatten somewhat into low lands and plains in the east of the country where the Danube flows.
Austria has a continental climate.
Austria is a democratic republic. The President of Austria is the head of state and the Chancellor of Austria is the head of government.
It is a neutral state, that means it does not take part in wars with other countries. It has been in the United Nations since 1955 and in the European Union since 1995.
Currently, the chancellor is Karl Nehammer The previous chancellor was Alexander Schallenberg (2021). Austria has been a member-state of the United Nations since 1955, the European Union since 1995 and OPEC since 2019.
Armenia (, "Hayastan"), officially the Republic of Armenia, is a landlocked country located in the Armenian Highlands, spanning Eastern Europe and Western Asia.
The Hittites and Hayasa-Azzi may have played a significant role in the ethnicity of Armenians. It has an ancient cultural heritage. One of the earliest Armenian kingdoms such as Urartu was established in 860 BC and by the 6th century BC it was replaced by the Satrapy of Armenia. The Kingdom of Armenia reached its height under Tigranes the Great in the 1st century BC and became the first state in the world to adopt Christianity as its official religion in the late 3rd or early 4th century AD. The official date of state adoption of Christianity is 301.
During World War I, Armenians living in their ancestral lands in the Ottoman Empire were systematically
exterminated in the Armenian Genocide, perpetrated by Ottoman Young Turks. Around 1.5 million people were slaughtered and many more deported. In 1918, following the Russian Revolution, all non-Russian countries declared their independence after the Russian Empire ceased to exist, leading to the establishment of the First Republic of Armenia. By 1920, the state was incorporated into the Transcaucasian Socialist Federative Soviet Republic, and in 1922 became a founding member of the Soviet Union. In 1936, the Transcaucasian state was dissolved, transforming its constituent states, including the Armenian Soviet Socialist Republic, into full Union republics. The modern Republic of Armenia became independent in 1991 during the dissolution of the Soviet Union.
Armenia is a Christian majority country, with European and some wider Eurasian cultural influences. The Republic of Armenia recognises the Armenian Apostolic Church, the world's oldest national church, as the country's primary religious establishment. The unique Armenian alphabet was invented by Mesrop Mashtots in 405 AD.
Armenia is a member of the Council of Europe, the Eurasian Economic Union and the Collective Security Treaty Organization. Armenia supports the de facto independent Republic of Artsakh, which was proclaimed in 1991.
When archaeologists do fieldwork, they look for remains, often by digging in the ground. As settlements (places where people lived in groups) change and grow, old buildings get buried. Usually, this is a natural process. A typical student project is to leave an object in a place where there is nothing going on. It will get covered rather quickly, because wind, water and plants will bury it. Sometimes buildings are deliberately buried to make way for new buildings. Ancient Rome, for example, is now up to 40 feet (12 metres) below the present city. This process of natural or man-made burial is why archaeological fieldwork involves digging, and is expensive and takes a long time.
Animals (or Metazoa) are living creatures with many cells. Animals get their energy from other living things. Usually, they eat them or are parasites. Animals, plants, fungi, and some other living things have complex cells, so they are grouped together as eukaryotes.
The study of animals is called zoology. The study of ancient life is called palaeontology.
Most animals are mobile, meaning they can move around. Animals take in oxygen, and give out carbon dioxide. This cellular respiration is part of their metabolism (chemical working). In both these ways they are different from plants. Also, the cells of animals have different cell membranes to other eukaryotes like plants and fungi.
There are many different types of animals. The common animals most people know are only about 3% of the animal kingdom. When biologists look at animals, they find things that certain animals have in common. They use this to group the animals in a biological classification. Several million species may exist, but biologists have only identified about one million.
Animals can mainly be divided into two main groups: the invertebrates and the vertebrates. Vertebrates have a backbone, or spine; invertebrates do not. Vertebrates are the only group to have an adaptive immune system, which may be partly responsible for their size and success.
The animal mode of nutrition is called heterotrophic because they get their food from other living organisms. Some animals eat only plants; they are called herbivores. Other animals eat only meat and are called carnivores. Animals that eat both plants and meat are called omnivores. Some animals get their energy from photosynthetic protists that live inside them.
The fossil record of animals goes back about 600 million years to the Ediacaran period, or somewhat earlier. During the whole of this long time, animals have been constantly evolving, so that the animals alive on Earth today are very different from those on the edges of the sea-floor in the Ediacaran.
In difficult situations, the acceleration can be calculated using mathematics: in calculus, acceleration is the derivative of the velocity (with respect to time), formula_10.
The formula of Newton's Second Law of Motion is formula_11,
where formula_12 is the acceleration, formula_13 is the force, and formula_14 the mass.
In Great Britain, blood sausage is called "black pudding". The ingredients include pig's blood, suet, bread, barley and oatmeal. Bury is well known for them. The most common kind of German "Blutwurst" is made from fatty pork meat, beef blood and filler such as barley. Though already cooked and "ready to eat" it is usually served warm.
A boot is a type of footwear that protects the foot and ankle. Boots are higher and larger than shoes and sandals. Some boots are high enough to protect the calves (lower part of the leg) as well. Some boots are held on with "bootstraps" or "bootlaces". Some also have spats or "gaiters" to keep water out. Most have a very strong "boot sole", the bottom part of a boot.
In many countries a company or business can ask the courts for "bankruptcy protection" to try and protect the business so that the creditors cannot destroy all of the physical capital and goodwill by breaking it apart and moving it away. The aim of this is to provide more time for the business to reorganise itself and to work out a new deal between the owners and the people with whom the business owes money. In many countries this is called "going into administration".
The journey of breakfast sausages began centuries ago in Europe, with each European country adding its unique twist. For instance, Germany is known for its variety of wursts, while Italian sausages often feature fennel and garlic. This evolution reflects changes in societal norms and eating habits, transitioning from a means of preservation to a convenient breakfast option.
Breakfast sausages are a good protein source but can be high in saturated fat and sodium. Leaner versions are available, and for those looking for plant-based alternatives, vegetarian sausages offer similar textures and flavors but are lower in fat and cholesterol-free.
Breakfast sausages are a staple in many cultures. In the US, they are often paired with pancakes and eggs. In the UK, they are a key part of the 'full English breakfast.' German Bratwurst and Italian sausages with fennel and garlic are examples of how different regions have embraced and adapted breakfast sausages.
Creative ways to incorporate breakfast sausages into meals include Sausage and Egg Muffin Cups, Sausage Breakfast Casseroles, and Sausage and Vegetable Skillets. These recipes demonstrate the versatility of breakfast sausages in various cuisines.