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Bearing (mechanical)
A bearing is a machine element that constrains relative motion to only the desired motion, and reduces friction between moving parts. The design of the bearing may, for example, provide for free linear movement of the moving part or for free rotation around a fixed axis; or, it may ''prevent'' a motion by controlling the vectors of normal forces that bear on the moving parts. Most bearings facilitate the desired motion by minimizing friction. Bearings are classified broadly according to the type of operation, the motions allowed, or to the directions of the loads (forces) applied to the parts. Rotary bearings hold rotating components such as shafts or axles within mechanical systems, and transfer axial and radial loads from the source of the load to the structure supporting it. The simplest form of bearing, the '' plain bearing'', consists of a shaft rotating in a hole. Lubrication is used to reduce friction. In the ''ball bearing'' and ''roller bearing'', to reduce slid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roller Bearing
In mechanical engineering, a rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing rolling elements (such as balls or rollers) between two concentric, grooved rings called races. The relative motion of the races causes the rolling elements to roll with very little rolling resistance and with little sliding. One of the earliest and best-known rolling-element bearings are sets of logs laid on the ground with a large stone block on top. As the stone is pulled, the logs roll along the ground with little sliding friction. As each log comes out the back, it is moved to the front where the block then rolls on to it. It is possible to imitate such a bearing by placing several pens or pencils on a table and placing an item on top of them. See " bearings" for more on the historical development of bearings. A rolling element rotary bearing uses a shaft in a much larger hole, and cylinders called "rollers" tightly fill the space between ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ball Bearing2
A ball is a round object (usually spherical, but can sometimes be ovoid) with several uses. It is used in ball games, where the play of the game follows the state of the ball as it is hit, kicked or thrown by players. Balls can also be used for simpler activities, such as catch or juggling. Balls made from hard-wearing materials are used in engineering applications to provide very low friction bearings, known as ball bearings. Black-powder weapons use stone and metal balls as projectiles. Although many types of balls are today made from rubber, this form was unknown outside the Americas until after the voyages of Columbus. The Spanish were the first Europeans to see the bouncing rubber balls (although solid and not inflated) which were employed most notably in the Mesoamerican ballgame. Balls used in various sports in other parts of the world prior to Columbus were made from other materials such as animal bladders or skins, stuffed with various materials. As balls are one of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Accuracy And Precision
Accuracy and precision are two measures of ''observational error''. ''Accuracy'' is how close a given set of measurements ( observations or readings) are to their '' true value'', while ''precision'' is how close the measurements are to each other. In other words, ''precision'' is a description of '' random errors'', a measure of statistical variability. ''Accuracy'' has two definitions: # More commonly, it is a description of only ''systematic errors'', a measure of statistical bias of a given measure of central tendency; low accuracy causes a difference between a result and a true value; ISO calls this ''trueness''. # Alternatively, ISO defines accuracy as describing a combination of both types of observational error (random and systematic), so high accuracy requires both high precision and high trueness. In the first, more common definition of "accuracy" above, the concept is independent of "precision", so a particular set of data can be said to be accurate, precise, both, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Agostino Ramelli
Agostino Ramelli (1531–ca. 1610) was an Italian engineer best known for writing and illustrating the book of engineering designs ''Le diverse et artificiose machine del Capitano Agostino Ramelli'', which contains, among others, his design for the bookwheel. Ramelli was born in Ponte Tresa or Mesanzena, today in Switzerland. During the Siege of La Rochelle (1572–1573), he successfully engineered a mine under a bastion and breached the fortification,"One Good Turn: A Natural History of the Screwdriver and Screw" Witold Rybczynski p.47 making him popular with his commander, Henri d'Anjou, who later became King Henri III of France. In 1588 Ramelli published ''Le diverse et artificiose machine del Capitano Agostino Ramelli'', or ''The various and ingenious machines of Captain Agostino Ramelli''. The book contains 195 designs, over 100 of which are water-raising machines, such as water pumps or wells.Brashear, RonaldRamelli's Machines Smithsonian Libraries. Other desig ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Leonardo Da Vinci
Leonardo di ser Piero da Vinci (15 April 14522 May 1519) was an Italian polymath of the High Renaissance who was active as a painter, Drawing, draughtsman, engineer, scientist, theorist, sculptor, and architect. While his fame initially rested on his achievements as a painter, he also became known for #Journals and notes, his notebooks, in which he made drawings and notes on a variety of subjects, including anatomy, astronomy, botany, cartography, painting, and paleontology. Leonardo is widely regarded to have been a genius who epitomized the Renaissance humanism, Renaissance humanist ideal, and his List of works by Leonardo da Vinci, collective works comprise a contribution to later generations of artists matched only by that of his younger contemporary, Michelangelo. Born Legitimacy (family law), out of wedlock to a successful Civil law notary, notary and a lower-class woman in, or near, Vinci, Tuscany, Vinci, he was educated in Florence by the Italian painter and sculptor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Italy
Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical region. Italy is also considered part of Western Europe, and shares land borders with France, Switzerland, Austria, Slovenia and the enclaved microstates of Vatican City and San Marino. It has a territorial exclave in Switzerland, Campione. Italy covers an area of , with a population of over 60 million. It is the third-most populous member state of the European Union, the sixth-most populous country in Europe, and the tenth-largest country in the continent by land area. Italy's capital and largest city is Rome. Italy was the native place of many civilizations such as the Italic peoples and the Etruscans, while due to its central geographic location in Southern Europe and the Mediterranean, the country has also historicall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lake Nemi
Lake Nemi ( it, Lago di Nemi, la, Nemorensis Lacus, also called Diana's Mirror, la, Speculum Dianae) is a small circular volcanic lake in the Lazio region of Italy south of Rome, taking its name from Nemi, the largest town in the area, that overlooks it from a height. Archaeology and history The lake is famous for its sunken Roman ships. These ships were very large and technologically advanced for their time. The lake was sacred to the goddess Diana Nemorensis and the site of the festival Nemoralia. Near the sanctuary of Diana were found a number of diminutive bronze statues of draped women and men, each holding libation bowls and incense boxes. Four of these figures are now in the British Museum's collection. Emperors Caligula and Tiberius sailed Lake Nemi not merely to cool off in summer, but to assert themselves as Nemorensis, rulers aligning with the Stars, wedded to Earth's perpetual life-force. Near the temple of Diana was the sacred grove of Aricia. Here there w ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Nemi Ships
The Nemi ships were two ships, one larger than the other, built under the reign of the Roman emperor Caligula in the 1st century CE on Lake Nemi. Although the purpose of the ships is only speculated upon, the larger ship was an elaborate floating palace, which contained quantities of marble, mosaic floors, heating and plumbing, and amenities such as baths. Both ships featured technology thought to have been developed historically much later. It has been stated that the emperor was influenced by the lavish lifestyles of the Hellenistic rulers of Syracuse and Ptolemaic Egypt. Recovered from the lake bed in 1929, the ships were destroyed by fire in 1944 during World War II. Location Lake Nemi ( it, Lago di Nemi, la, Nemorensis Lacus) is a small circular volcanic lake in the Lazio region of Italy, south of Rome. It has a surface of and a maximum depth of . There is considerable speculation regarding why the emperor Caligula chose to build two large ships on such a small la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Roman Republic
The Roman Republic ( la, Res publica Romana ) was a form of government of Rome and the era of the classical Roman civilization when it was run through public representation of the Roman people. Beginning with the overthrow of the Roman Kingdom (traditionally dated to 509 BC) and ending in 27 BC with the establishment of the Roman Empire, Rome's control rapidly expanded during this period—from the city's immediate surroundings to hegemony over the entire Mediterranean world. Roman society under the Republic was primarily a cultural mix of Latin and Etruscan societies, as well as of Sabine, Oscan, and Greek cultural elements, which is especially visible in the Roman Pantheon. Its political organization developed, at around the same time as direct democracy in Ancient Greece, with collective and annual magistracies, overseen by a senate. The top magistrates were the two consuls, who had an extensive range of executive, legislative, judicial, military, and religious po ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wheel
A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be moved easily facilitating movement or transportation while supporting a load, or performing labor in machines. Wheels are also used for other purposes, such as a ship's wheel, steering wheel, potter's wheel, and flywheel. Common examples are found in transport applications. A wheel reduces friction by facilitating motion by rolling together with the use of axles. In order for wheels to rotate, a moment needs to be applied to the wheel about its axis, either by way of gravity or by the application of another external force or torque. Using the wheel, Sumerians invented a device that spins clay as a potter shapes it into the desired object. Terminology The English word '' wheel'' comes from the Old English word , from Proto-Germanic , f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hand Drill
A hand drill is the simplest primitive method to produce rapid rotary motion of a rod. It consists in holding the rod vertically between both hands and moving these back and forth, in opposite directions, as in rubbing them. The rod typically is one or two feet long and half an inch in diameter. Hand drills have been used by many primitive societies as a fire drill to start a fire. It is still often learned as a useful survival skill. A hand drill could also be used as a tool for drilling holes in hard materials such as wood, stone, or bone. For either use, the hands must also exert downward pressure while spinning the rod. As a result, the hands drift down the rod, and must be periodically raised to the top again. These interruptions can be avoided by cutting a notch at the top of the shaft, tying a cord through it, and then inserting the thumbs through loops in the cord. However, skilled operators can either maintain pressure with their hands almost stationary ver ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Djehutihotep
Djehutihotep ("''Thoth is satisfied''") was an ancient Egyptian nomarch of the fifteenth '' nomos'' of Upper Egypt (''" the Hare"'') during the twelfth dynasty, c. 1900 BC. Biography Djehutihotep lived under the reigns of Amenemhat II, Senusret II, and Senusret III and was one of the most powerful nomarchs of the Middle Kingdom. His tomb—the only one among the necropolis of Deir el-Bersha that wasn't damaged by the explosives used in recent quarrying methods—is well known for the great quality of its decorations, a work carried out by an artist named Amenaankhu. For this reason, it is believed that Djehutihotep died prior to the strict measures reducing the power of the nomarchs that were established by Senusret III. Indeed, as their charge became hereditary at the end of the Old Kingdom, the nomarchs became local rulers effectively, although not nominally, independent of the pharaohs. This situation led to excesses in the exercise of power that worsened steadil ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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