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Ball
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 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mesoamerican Ballgame
The Mesoamerican ballgame ( nah, ōllamalīztli, , myn, pitz) was a sport with ritual associations played since at least 1650 BC by the pre-Columbian people of Ancient Mesoamerica. The sport had different versions in different places during the millennia, and a newer, more modern version of the game, ''ulama'', is still played by the indigenous populations in some places.Fox, John (2012)''The ball: discovering the object of the game"'' 1st ed., New York: Harper. . Cf. Chapter 4: "Sudden Death in the New World" about the Ulama game. The rules of the Mesoamerican ballgame are not known, but judging from its descendant, ulama, they were probably similar to racquetball, where the aim is to keep the ball in play. The stone ballcourt goals are a late addition to the game. In the most common theory of the game, the players struck the ball with their hips, although some versions allowed the use of forearms, rackets, bats, or handstones. The ball was made of solid rubber and weigh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ball Game
This is a list of ball games and ball sports that include a ball as a key element in the activity, usually for scoring points. Ball games Ball sports fall within many sport categories, some sports within multiple categories, including: *Bat-and-ball games, such as cricket and baseball. * Invasion games, such as football and basketball. *Net and wall games, such as volleyball. **Racket sports, such as tennis, table tennis and badminton. *Throwing sports, such as dodgeball and bocce. **Cue sports, such as pool and snooker. **Target sports, such as golf and bowling. * Hand and ball-striking games, such as various handball codes, rebound handball, and four square. Popular ball games Games that are similar and have a common reference are grouped under the primary name such as bowling, football and hockey. A - E * Angleba * Apalachee ball game ** Crossminton * Bandy ** Rink bandy *** Rinkball * Baseball ** Baseball5 * Basketball ** 3x3 (basketball) ** Wheelchair basketball * Basque ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ball Bearings
A ball bearing is a type of rolling-element bearing that uses balls to maintain the separation between the bearing races. The purpose of a ball bearing is to reduce rotational friction and support radial and axial loads. It achieves this by using at least two races to contain the balls and transmit the loads through the balls. In most applications, one race is stationary and the other is attached to the rotating assembly (e.g., a hub or shaft). As one of the bearing races rotates it causes the balls to rotate as well. Because the balls are rolling they have a much lower coefficient of friction than if two flat surfaces were sliding against each other. Ball bearings tend to have lower load capacity for their size than other kinds of rolling-element bearings due to the smaller contact area between the balls and races. However, they can tolerate some misalignment of the inner and outer races. History Although bearings had been developed since ancient times, the first m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Juggling
Juggling is a physical skill, performed by a juggler, involving the manipulation of objects for recreation, entertainment, art or sport. The most recognizable form of juggling is toss juggling. Juggling can be the manipulation of one object or many objects at the same time, most often using one or two hands but also possible with feet. Jugglers often refer to the objects they juggle as ''props''. The most common props are balls, clubs, or rings. Some jugglers use more dramatic objects such as knives, fire torches or chainsaws. The term ''juggling'' can also commonly refer to other prop-based manipulation skills, such as diabolo, plate spinning, devil sticks, poi, cigar boxes, contact juggling, hooping, yo-yo, and hat manipulation. Etymology The words ''juggling'' and ''juggler'' derive from the Middle English ''jogelen'' ("to entertain by performing tricks"), which in turn is from the Old French '' jangler''. There is also the Late Latin form ''joculare'' of Latin ' ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sphere
A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the centre of the sphere, and is the sphere's radius. The earliest known mentions of spheres appear in the work of the ancient Greek mathematicians. The sphere is a fundamental object in many fields of mathematics. Spheres and nearly-spherical shapes also appear in nature and industry. Bubbles such as soap bubbles take a spherical shape in equilibrium. The Earth is often approximated as a sphere in geography, and the celestial sphere is an important concept in astronomy. Manufactured items including pressure vessels and most curved mirrors and lenses are based on spheres. Spheres roll smoothly in any direction, so most balls used in sports and toys are spherical, as are ball bearings. Basic terminology As mentioned earlier is th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Projectile
A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found in warfare and sports (for example, a thrown baseball, kicked football, fired bullet, shot arrow, stone released from catapult). In ballistics mathematical equations of motion are used to analyze projectile trajectories through launch, flight, and impact. Motive force Blowguns and pneumatic rifles use compressed gases, while most other guns and cannons utilize expanding gases liberated by sudden chemical reactions by propellants like smokeless powder. Light-gas guns use a combination of these mechanisms. Railguns utilize electromagnetic fields to provide a constant acceleration along the entire length of the device, greatly increasing the muzzle velocity. Some projectiles provide propulsion during flight by means of a rock ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rubber
Rubber, also called India rubber, latex, Amazonian rubber, ''caucho'', or ''caoutchouc'', as initially produced, consists of polymers of the organic compound isoprene, with minor impurities of other organic compounds. Thailand, Malaysia, and Indonesia are three of the leading rubber producers. Types of polyisoprene that are used as natural rubbers are classified as elastomers. Currently, rubber is harvested mainly in the form of the latex from the rubber tree (''Hevea brasiliensis'') or others. The latex is a sticky, milky and white colloid drawn off by making incisions in the bark and collecting the fluid in vessels in a process called "tapping". The latex then is refined into the rubber that is ready for commercial processing. In major areas, latex is allowed to coagulate in the collection cup. The coagulated lumps are collected and processed into dry forms for sale. Natural rubber is used extensively in many applications and products, either alone or in combination ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and Borders of China, borders fourteen countries by land, the List of countries and territories by land borders, most of any country in the world, tied with Russia. Covering an area of approximately , it is the world's third List of countries and dependencies by area, largest country by total land area. The country consists of 22 provinces of China, provinces, five autonomous regions of China, autonomous regions, four direct-administered municipalities of China, municipalities, and two special administrative regions of China, Special Administrative Regions (Hong Kong and Macau). The national capital is Beijing, and the List of cities in China by population, most populous cit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Black Powder
Gunpowder, also commonly known as black powder to distinguish it from modern smokeless powder, is the earliest known chemical explosive. It consists of a mixture of sulfur, carbon (in the form of charcoal) and potassium nitrate (saltpeter). The sulfur and carbon act as fuels while the saltpeter is an oxidizer. Gunpowder has been widely used as a propellant in firearms, artillery, rocketry, and pyrotechnics, including use as a blasting agent for explosives in quarrying, mining, building pipelines and road building. Gunpowder is classified as a low explosive because of its relatively slow decomposition rate and consequently low brisance. Low explosives deflagrate (i.e., burn at subsonic speeds), whereas high explosives detonate, producing a supersonic shockwave. Ignition of gunpowder packed behind a projectile generates enough pressure to force the shot from the muzzle at high speed, but usually not enough force to rupture the gun barrel. It thus makes a good propellant but is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Human Baby
An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to refer to juveniles of other organisms. A newborn is, in colloquial use, an infant who is only hours, days, or up to one month old. In medical contexts, a newborn or neonate (from Latin, ''neonatus'', newborn) is an infant in the first 28 days after birth; the term applies to premature, full term, and postmature infants. Before birth, the offspring is called a fetus. The term ''infant'' is typically applied to very young children under one year of age; however, definitions may vary and may include children up to two years of age. When a human child learns to walk, they are called a toddler instead. Other uses In British English, an ''infant school'' is for children aged between four and seven. As a legal term, ''infancy'' is more li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cognate
In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical effects on both the sound and the meaning of a word, cognates may not be obvious, and often it takes rigorous study of historical sources and the application of the comparative method to establish whether lexemes are cognate or not. Cognates are distinguished from loanwords, where a word has been borrowed from another language. The term ''cognate'' derives from the Latin noun '' cognatus blood relative'. Characteristics Cognates need not have the same meaning, which may have changed as the languages developed independently. For example English '' starve'' and Dutch '' sterven'' 'to die' or German '' sterben'' 'to die' all descend from the same Proto-Germanic verb, '' *sterbaną'' 'to die'. Cognates also do not need to look or sound sim ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Engineering
Engineering is the use of scientific principles to design and build machines, structures, and other items, including bridges, tunnels, roads, vehicles, and buildings. The discipline of engineering encompasses a broad range of more specialized fields of engineering, each with a more specific emphasis on particular areas of applied mathematics, applied science, and types of application. See glossary of engineering. The term ''engineering'' is derived from the Latin ''ingenium'', meaning "cleverness" and ''ingeniare'', meaning "to contrive, devise". Definition The American Engineers' Council for Professional Development (ECPD, the predecessor of ABET) has defined "engineering" as: The creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
