1.
Baba Vida
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Baba Vida is a medieval fortress in Vidin in northwestern Bulgaria and the towns primary landmark. Baba Vida is 39 metres above sea level, the construction of the fortress began in the 10th century at the place of the Ancient Roman castell Bononia. The building of Baba Vida is tied to a legend, according to which a Danubian Bulgarian king who ruled at Vidin had three daughters, Vida, Kula and Gamza, prior to his death, he divided his realm among the three. Vida, the eldest, was given Vidin and the north to the Carpathians, Kula was awarded Zaječar and the Timok Valley. Although Gamza and Kula married to drunkard and warlike nobles, Vida remained unmarried, the name of the castle means Granny Vida. Baba Vida served as Vidins main defensive installation during the course of the Middle Ages, the Baba Vida stronghold stood an eight-month-long siege by Byzantine forces led by Basil II, but was destroyed and once again erected during the rule of Ivan Stratsimir, as whose capital it served. Between 1365 and 1369, the fortress was in Hungarian hands, Vidin was suddenly attacked by the forces of Louis I of Hungary, but it took several months to conquer Baba Vida. In 1369, Ivan Sratsimir managed to control of his capital. In 1388, the Ottomans invaded Sratsimirs lands and forced him to become their vassal, in 1396, he joined an anti-Ottoman crusade led by the King of Hungary, Sigismund, placing his resources at the crusaders disposal. The crusade ended in the disastrous Battle of Nicopolis at Nikopol, Bulgaria, with the Ottomans capturing most of Sratsimirs domains shortly thereafter, today, Baba Vida castle functions as a museum. Being a popular tourist attraction, the fortress is being kept in repair, website about Baba Vida Baba Vida at Vidin-Info Baba Vida at Travel. Pop. bg
2.
Vidin
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Vidin is a port town on the southern bank of the Danube in north-western Bulgaria. It is close to the borders with Romania and Serbia, and is also the centre of Vidin Province. An agricultural and trade centre, Vidin has a fertile hinterland renowned for its wines, the name is archaically spelled as Widdin in English. Old name Dunonia itself meant fortified hill in Celtic with the typically dun found frequently in Celtic place names, Vidin is the westernmost important Bulgarian Danube port and is situated on one of the southernmost sections of the river. The New Europe Bridge, completed in 2013, connects Vidin to the Romanian town of Calafat on the bank of the Danube. Previously, a ferry located 2 km from the town was in use for that purpose, Vidin emerged at the place of an old Celtic settlement known as Dunonia. The settlement evolved into a Roman fortified town called Bononia, the town grew into one of the important centres of the province of Upper Moesia, encompassing the territory of modern north-western Bulgaria and eastern Serbia. When Slavs settled in the area, they called the town Badin or Bdin, similarly, Anna Komnene refers to it as Vidynē in the Alexiad. Vidins main landmark, the Baba Vida fortress, was built in the period from the 10th to the 14th century, in the Middle Ages Vidin used to be an important Bulgarian city, a bishop seat and capital of a large province. Between 971 and 976 the town was the center of Samuils possessions while his brothers ruled to the south, in 1003 Vidin was seized by Basil II after an eight-month siege because of the betrayal of the local bishop. Its importance once again rose during the Second Bulgarian Empire and its despots were influential figures in the Empire and were on several occasions chosen for Emperors, from the mid 13th century it was ruled by the Shishman family. In 1356, Bulgarian Tsar Ivan Alexander isolated Vidin from the Bulgarian monarchy, in 1365, the Tsardom of Vidin was occupied by Magyar crusaders. Under Hungarian rule, the city known as Bodony. In 1369, the Second Bulgarian empire drove out the Hungarian military, the Ottomans went on to conquer the despotates of Dobrudzha, Prilep and Velbazhd as well. Vidins independence did not last long, in 1396 the Ottomans invaded and turned Vidin into a sanjdak. In the late years of Ottoman rule, Vidin was the centre of Turkish rebel Osman Pazvantoğlus breakaway state. In 1853, The Times of London reported that Widdin, as it was called, was a town, with a population of about 26,000. Widdin is one of the important fortified places of the line of the Danube
3.
Bulgaria
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Bulgaria, officially the Republic of Bulgaria, is a country in southeastern Europe. It is bordered by Romania to the north, Serbia and Macedonia to the west, Greece and Turkey to the south, with a territory of 110,994 square kilometres, Bulgaria is Europes 16th-largest country. Organised prehistoric cultures began developing on current Bulgarian lands during the Neolithic period and its ancient history saw the presence of the Thracians, Greeks, Persians, Celts, Romans, Goths, Alans and Huns. With the downfall of the Second Bulgarian Empire in 1396, its territories came under Ottoman rule for five centuries. The Russo-Turkish War of 1877–78 led to the formation of the Third Bulgarian State, the following years saw several conflicts with its neighbours, which prompted Bulgaria to align with Germany in both world wars. In 1946 it became a one-party socialist state as part of the Soviet-led Eastern Bloc, in December 1989 the ruling Communist Party allowed multi-party elections, which subsequently led to Bulgarias transition into a democracy and a market-based economy. Bulgarias population of 7.2 million people is predominantly urbanised, most commercial and cultural activities are centred on the capital and largest city, Sofia. The strongest sectors of the economy are industry, power engineering. The countrys current political structure dates to the adoption of a constitution in 1991. Bulgaria is a parliamentary republic with a high degree of political, administrative. Human activity in the lands of modern Bulgaria can be traced back to the Paleolithic, animal bones incised with man-made markings from Kozarnika cave are assumed to be the earliest examples of symbolic behaviour in humans. Organised prehistoric societies in Bulgarian lands include the Neolithic Hamangia culture, Vinča culture, the latter is credited with inventing gold working and exploitation. Some of these first gold smelters produced the coins, weapons and jewellery of the Varna Necropolis treasure and this site also offers insights for understanding the social hierarchy of the earliest European societies. Thracians, one of the three primary groups of modern Bulgarians, began appearing in the region during the Iron Age. In the late 6th century BC, the Persians conquered most of present-day Bulgaria, and kept it until 479 BC. After the division of the Roman Empire in the 5th century the area fell under Byzantine control, by this time, Christianity had already spread in the region. A small Gothic community in Nicopolis ad Istrum produced the first Germanic language book in the 4th century, the first Christian monastery in Europe was established around the same time by Saint Athanasius in central Bulgaria. From the 6th century the easternmost South Slavs gradually settled in the region, in 680 Bulgar tribes under the leadership of Asparukh moved south across the Danube and settled in the area between the lower Danube and the Balkan, establishing their capital at Pliska
4.
Siege engine
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A siege engine is a device that is designed to break or circumvent city walls and other fortifications in siege warfare. Some have been operated close to the fortifications, while others have used to attack from a distance. From antiquity, siege engines were constructed largely of wood and tended to use mechanical advantage to fling stones, with the development of gunpowder and improved metallurgical techniques, siege engines became artillery. Collectively, siege engines or artillery together with the necessary troops, the earliest engine was the battering ram, developed by the Assyrians, followed by the catapult in ancient Greece. The first Mediterranean people to use advanced siege machinery were the Carthaginians and these engines influenced the ruler of Syracuse, Dionysius I, who developed a catapult in 399 BC. The first two rulers to use of siege engines to a large extent were Philip II of Macedonia. The most utilized engines were simple battering rams, or tortoises, for sea sieges or battles, seesaw-like machines were used. These were giant ladders, hinged and mounted on a base mechanism and they were normally mounted on two or more ships tied together and some sambykē included shields at the top to protect the climbers from arrows. Other hinged engines were used to catch enemy equipment or even opposing soldiers with opposable appendices which are probably ancestors to the Roman corvus, other weapons dropped heavy weights on opposing soldiers. The Romans preferred to assault enemy walls by building earthen ramps or simply scaling the walls, soldiers working at the ramps were protected by shelters called vineae, that were arranged to form a long corridor. Wicker shields were used to protect the front of the corridor during its construction, another Roman siege engine sometimes used resembled the Greek ditch-filling tortoise, called a musculus. The Roman Legions first used siege towers around 200 BC, the first documented occurrence of ancient siege artillery pieces in Europe was the gastraphetes, a kind of large crossbow. These were mounted on wooden frames, greater machines forced the introduction of pulley system for loading the projectiles, which had extended to include stones also. Later torsion systems appeared, based on sinew springs, the onager was the main Roman invention in the field. Much of what we now know of the technology of the time came to us from Books 14 and 15 on Siege Warfare from the Mo Jing. Recorded and preserved on bamboo strips, much of the text is now unfortunately extremely corrupted, medieval designs include a large number of catapults such as the Mangonel, Onager, the ballista, the traction trebuchet, and the counterweight trebuchet. These machines used mechanical energy to fling large projectiles to batter down stone walls, also used were the battering ram and the siege tower, a wooden tower on wheels that allowed attackers to climb up and over castle walls, while protected somewhat from enemy arrows. Another weapon was the petard, a device designed specifically for breaching gates
5.
Ancient history
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Ancient history is the aggregate of past events from the beginning of recorded human history and extending as far as the Early Middle Ages or the Postclassical Era. The span of recorded history is roughly 5,000 years, beginning with Sumerian Cuneiform script, the term classical antiquity is often used to refer to history in the Old World from the beginning of recorded Greek history in 776 BC. This roughly coincides with the date of the founding of Rome in 753 BC, the beginning of the history of ancient Rome. In India, ancient history includes the period of the Middle Kingdoms, and, in China. Historians have two major avenues which they take to better understand the ancient world, archaeology and the study of source texts, primary sources are those sources closest to the origin of the information or idea under study. Primary sources have been distinguished from secondary sources, which cite, comment on. Archaeology is the excavation and study of artefacts in an effort to interpret, archaeologists excavate the ruins of ancient cities looking for clues as to how the people of the time period lived. The study of the ancient cities of Harappa, Mohenjo-daro, the city of Pompeii, an ancient Roman city preserved by the eruption of a volcano in AD79. Its state of preservation is so great that it is a window into Roman culture and provided insight into the cultures of the Etruscans. The Terracotta Army, the mausoleum of the First Qin Emperor in ancient China, the discovery of Knossos by Minos Kalokairinos and Sir Arthur Evans. The discovery of Troy by Heinrich Schliemann, most of what is known of the ancient world comes from the accounts of antiquitys own historians. Although it is important to take account the bias of each ancient author. Some of the more notable ancient writers include Herodotus, Thucydides, Arrian, Plutarch, Polybius, Sima Qian, Sallust, Livy, Josephus, Suetonius, furthermore, the reliability of the information obtained from these surviving records must be considered. Few people were capable of writing histories, as literacy was not widespread in almost any culture until long after the end of ancient history, the earliest known systematic historical thought emerged in ancient Greece, beginning with Herodotus of Halicarnassus. He was also the first to distinguish between cause and immediate origins of an event, the Roman Empire was one of the ancient worlds most literate cultures, but many works by its most widely read historians are lost. Indeed, only a minority of the work of any major Roman historian has survived, prehistory is the period before written history. The early human migrations in the Lower Paleolithic saw Homo erectus spread across Eurasia 1.8 million years ago, the controlled use of fire occurred 800,000 years ago in the Middle Paleolithic. 250,000 years ago, Homo sapiens emerged in Africa, 60–70,000 years ago, Homo sapiens migrated out of Africa along a coastal route to South and Southeast Asia and reached Australia
6.
Fortification
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Fortifications are military constructions or buildings designed for the defense of territories in warfare, and also used to solidify rule in a region during peace time. Humans have constructed defensive works for many thousands of years, in a variety of increasingly complex designs, the term is derived from the Latin fortis and facere. From very early history to modern times, walls have been a necessity for cities to survive in a changing world of invasion. Some settlements in the Indus Valley Civilization were the first small cities to be fortified, in ancient Greece, large stone walls had been built in Mycenaean Greece, such as the ancient site of Mycenae. A Greek Phrourion was a collection of buildings used as a military garrison. These construction mainly served the purpose of a tower, to guard certain roads, passes. Though smaller than a fortress, they acted as a border guard rather than a real strongpoint to watch. The art of setting out a camp or constructing a fortification traditionally has been called castramentation since the time of the Roman legions. Fortification is usually divided into two branches, permanent fortification and field fortification, there is also an intermediate branch known as semi-permanent fortification. Castles are fortifications which are regarded as being distinct from the fort or fortress in that they are a residence of a monarch or noble. Roman forts and hill forts were the antecedents of castles in Europe. The Early Middle Ages saw the creation of towns built around castles. Medieval-style fortifications were made obsolete by the arrival of cannons in the 14th century. Fortifications in the age of black powder evolved into much lower structures with greater use of ditches and earth ramparts that would absorb, Walls exposed to direct cannon fire were very vulnerable, so were sunk into ditches fronted by earth slopes. The arrival of explosive shells in the 19th century led to yet another stage in the evolution of fortification, steel-and-concrete fortifications were common during the 19th and early 20th centuries. However the advances in warfare since World War I have made large-scale fortifications obsolete in most situations. Demilitarized zones along borders are arguably another type of fortification, although a passive kind, many military installations are known as forts, although they are not always fortified. Larger forts may be called fortresses, smaller ones were known as fortalices
7.
Momentum
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In classical mechanics, linear momentum, translational momentum, or simply momentum is the product of the mass and velocity of an object, quantified in kilogram-meters per second. It is dimensionally equivalent to impulse, the product of force and time, Newtons second law of motion states that the change in linear momentum of a body is equal to the net impulse acting on it. If the truck were lighter, or moving slowly, then it would have less momentum. Linear momentum is also a quantity, meaning that if a closed system is not affected by external forces. In classical mechanics, conservation of momentum is implied by Newtons laws. It also holds in special relativity and, with definitions, a linear momentum conservation law holds in electrodynamics, quantum mechanics, quantum field theory. It is ultimately an expression of one of the symmetries of space and time. Linear momentum depends on frame of reference, observers in different frames would find different values of linear momentum of a system. But each would observe that the value of linear momentum does not change with time, momentum has a direction as well as magnitude. Quantities that have both a magnitude and a direction are known as vector quantities, because momentum has a direction, it can be used to predict the resulting direction of objects after they collide, as well as their speeds. Below, the properties of momentum are described in one dimension. The vector equations are almost identical to the scalar equations, the momentum of a particle is traditionally represented by the letter p. It is the product of two quantities, the mass and velocity, p = m v, the units of momentum are the product of the units of mass and velocity. In SI units, if the mass is in kilograms and the velocity in meters per second then the momentum is in kilogram meters/second, in cgs units, if the mass is in grams and the velocity in centimeters per second, then the momentum is in gram centimeters/second. Being a vector, momentum has magnitude and direction, for example, a 1 kg model airplane, traveling due north at 1 m/s in straight and level flight, has a momentum of 1 kg m/s due north measured from the ground. The momentum of a system of particles is the sum of their momenta, if two particles have masses m1 and m2, and velocities v1 and v2, the total momentum is p = p 1 + p 2 = m 1 v 1 + m 2 v 2. If all the particles are moving, the center of mass will generally be moving as well, if the center of mass is moving at velocity vcm, the momentum is, p = m v cm. This is known as Eulers first law, if a force F is applied to a particle for a time interval Δt, the momentum of the particle changes by an amount Δ p = F Δ t
8.
Tension (physics)
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Tension is the opposite of compression. At the atomic level, when atoms or molecules are pulled apart each other and gain potential energy with a restoring force still existing. Each end of a string or rod under such tension will pull on the object it is attached to, to restore the string/rod to its relaxed length. In physics, tension, as a force, as an action-reaction pair of forces. The ends of a string or other object transmitting tension will exert forces on the objects to which the string or rod is connected and these forces due to tension are also called passive forces. Tension in a string is a scalar quantity. A string or rope is often idealized as one dimension, having length but being massless with zero cross section. If there are no bends in the string, as occur with vibrations or pulleys, then tension is a constant along the string, by Newtons Third Law, these are the same forces exerted on the ends of the string by the objects to which the ends are attached. If the string curves around one or more pulleys, it still have constant tension along its length in the idealized situation that the pulleys are massless and frictionless. A vibrating string vibrates with a set of frequencies that depend on the strings tension and these frequencies can be derived from Newtons laws of motion. Each microscopic segment of the string pulls on and is pulled upon by its neighboring segments, tension = τ where x is the position along the string. If the string has curvature, then the two pulls on a segment by its two neighbors will not add to zero, and there will be a net force on that segment of the string, causing an acceleration. With solutions that include the various harmonics on a stringed instrument, tension is also used to describe the force exerted by the ends of a three-dimensional, continuous material such as a rod or truss member. Such a rod elongates under tension, a system is in equilibrium when the sum of all forces is zero. ∑ F → =0 For example, consider a system consisting of an object that is being lowered vertically by a string with tension, T, at a constant velocity. ∑ F → = T → + m g → =0 A system has a net force when a force is exerted on it. Acceleration and net force always exist together, ∑ F → ≠0 For example, consider the same system as above but suppose the object is now being lowered with an increasing velocity downwards therefore there exists a net force somewhere in the system. In this case, negative acceleration would indicate that | m g | > | T |
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