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Throw (engineering)
Throwing is an action which consists in acceleration, accelerating a projectile and then releasing it so that it follows a ballistics, ballistic trajectory, usually with the aim of impact (mechanics), impacting a remote target. This action is best characterized for animals with prehensibility, prehensile limbs: in this case the projectile is grasping, grasped, while the limb segments impart a motion of the hand through compounded mechanical advantage. For other animals, the definition of throwing is somewhat unclear, as other actions such as spitting or Spray (liquid drop), spraying may or may not be included. Primates are the most capable throwers in the animal kingdom, and they typically throw feces as a form of agonistic behavior. Of all primates, humans are by far the most capable throwers. They throw a large variety of projectiles, with a much greater efficacy and accuracy. Humans have thrown projectiles for hunting and in warfare – first through rock throwing, rock-thro ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rock Throwing
Stone throwing or rock throwing, when it is directed at another person (called stone pelting in India), is often considered a form of criminal battery. History The throwing of rocks or stones is one of the most ancient forms of ranged-weapon combat, with stone-throwing slings found among other weapons in the tomb of Tutankhamen, who died about 1325 BC. Xenophon mentions in his Hellenica the petrobóloi ( grc, πετροβόλοι), and Thucydides in the History of the Peloponnesian War and Dio Cassius in his Histories mention the lithobóloi ( grc, λιθοβόλοι), both meaning stone-throwers in Greek, as army units. De re militari (Latin "Concerning Military Matters") by the Roman writer Publius Flavius Vegetius Renatus details Roman soldiers training to throw stones as weapons. "Recruits are to be taught the art of throwing stones both with the hand and sling." And "Formerly all soldiers were trained to the practice of throwing stones of a pound weight with the h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Games
A game is a structured form of play, usually undertaken for entertainment or fun, and sometimes used as an educational tool. Many games are also considered to be work (such as professional players of spectator sports or games) or art (such as jigsaw puzzles or games involving an artistic layout such as Mahjong, solitaire, or some video games). Games are sometimes played purely for enjoyment, sometimes for achievement or reward as well. They can be played alone, in teams, or online; by amateurs or by professionals. The players may have an audience of non-players, such as when people are entertained by watching a chess championship. On the other hand, players in a game may constitute their own audience as they take their turn to play. Often, part of the entertainment for children playing a game is deciding who is part of their audience and who is a player. A toy and a game are not the same. Toys generally allow for unrestricted play whereas games come with present rules. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sports
Sport pertains to any form of competitive physical activity or game that aims to use, maintain, or improve physical ability and skills while providing enjoyment to participants and, in some cases, entertainment to spectators. Sports can, through casual or organized participation, improve participants' physical health. Hundreds of sports exist, from those between single contestants, through to those with hundreds of simultaneous participants, either in teams or competing as individuals. In certain sports such as racing, many contestants may compete, simultaneously or consecutively, with one winner; in others, the contest (a ''match'') is between two sides, each attempting to exceed the other. Some sports allow a "tie" or "draw", in which there is no single winner; others provide tie-breaking methods to ensure one winner and one loser. A number of contests may be arranged in a tournament producing a champion. Many sports leagues make an annual champion by arranging games in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Exercise
Exercise is a body activity that enhances or maintains physical fitness and overall health and wellness. It is performed for various reasons, to aid growth and improve strength, develop muscles and the cardiovascular system, hone athletic skills, weight loss or maintenance, improve health, or simply for enjoyment. Many individuals choose to exercise outdoors where they can congregate in groups, socialize, and improve well-being as well as mental health. In terms of health benefits, the amount of recommended exercise depends upon the goal, the type of exercise, and the age of the person. Even doing a small amount of exercise is healthier than doing none. Classification Physical exercises are generally grouped into three types, depending on the overall effect they have on the human body: * Aerobic exercise is any physical activity that uses large muscle groups and causes the body to use more oxygen than it would while resting. The goal of aerobic exercise is to increa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Recreation
Recreation is an activity of leisure, leisure being discretionary time. The "need to do something for recreation" is an essential element of human biology and psychology. Recreational activities are often done for enjoyment, amusement, or pleasure and are considered to be "fun". Etymology The term ''recreation'' appears to have been used in English first in the late 14th century, first in the sense of "refreshment or curing of a sick person", and derived turn from Latin (''re'': "again", ''creare'': "to create, bring forth, beget"). Prerequisites to leisure People spend their time on activities of daily living, work, sleep, social duties and leisure, the latter time being free from prior commitments to physiologic or social needs, a prerequisite of recreation. Leisure has increased with increased longevity and, for many, with decreased hours spent for physical and economic survival, yet others argue that time pressure has increased for modern people, as they are committed to too ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ranged Weapons
A ranged weapon is any weapon that can engage targets beyond hand-to-hand distance, i.e. at distances greater than the physical reach of the user holding the weapon itself. The act of using such a weapon is also known as shooting. It is sometimes also called projectile weapon or missile weapon because it typically works by launching solid projectiles ("missiles"), though technically a fluid-projector (which throws out pressurized streams of liquid or even gas) and a directed-energy weapon (which does not involve any tangible projectile) are also ranged weapons. In contrast, a weapon intended to be used in hand-to-hand combat is called a melee weapon. Ranged weapons give the attacker an advantage, since the target is often getting hit from beyond immediate visual range, therefore making it more difficult for the defenders to react and hitting back effectively. It also puts distance between the attacker and the opponent, which is a safer combat option since the close physical ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gun 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 propellan ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mechanism (engineering)
In engineering, a mechanism is a Machine, device that transforms input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components which may include: * Gears and gear trains; * belt drive, Belts and chain drives; * Cams and cam follower, followers; * Linkage (mechanical), Linkages; * Friction devices, such as brakes or clutches; * Structural components such as a frame, fasteners, bearings, springs, or lubricants; * Various machine elements, such as splines, pins, or keys. The German scientist Franz Reuleaux defines ''machine'' as "a combination of resistant bodies so arranged that by their means the mechanical forces of nature can be compelled to do work accompanied by certain determinate motion". In this context, his use of ''machine'' is generally interpreted to mean ''mechanism''. The combination of force and movement defines Power (physics), power, and a mechanism manages power to achieve a desired set of forces and ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Catapult
A catapult is a ballistic device used to launch a projectile a great distance without the aid of gunpowder or other propellants – particularly various types of ancient and medieval siege engines. A catapult uses the sudden release of stored potential energy to propel its payload. Most convert tension or torsion energy that was more slowly and manually built up within the device before release, via springs, bows, twisted rope, elastic, or any of numerous other materials and mechanisms. In use since ancient times, the catapult has proven to be one of the most persistently effective mechanisms in warfare. In modern times the term can apply to devices ranging from a simple hand-held implement (also called a "slingshot") to a mechanism for launching aircraft from a ship. The earliest catapults date to at least the 7th century BC, with King Uzziah, of Judah, recorded as equipping the walls of Jerusalem with machines that shot "great stones". Catapults are mentioned in Yajurveda un ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bow And Arrow
The bow and arrow is a ranged weapon system consisting of an elastic launching device (bow) and long-shafted projectiles ( arrows). Humans used bows and arrows for hunting and aggression long before recorded history, and the practice was common to many prehistoric cultures. They were important weapons of war from ancient history until the early modern period, where they were rendered increasingly obsolete by the development of the more powerful and accurate firearms. Today, bows and arrows are mostly used for hunting and sports. Archery is the art, practice, or skill of using bows to shoot arrows.Paterson ''Encyclopaedia of Archery'' p. 17 A person who shoots arrows with a bow is called a bowman or an archer. Someone who makes bows is known as a bowyer,Paterson ''Encyclopaedia of Archery'' p. 31 someone who makes arrows is a fletcher,Paterson ''Encyclopaedia of Archery'' p. 56 and someone who manufactures metal arrowheads is an arrowsmith.Paterson ''Encyclopaedia of Arche ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sling (weapon)
A sling is a projectile weapon typically used to throw a blunt projectile such as a stone, clay, or lead " sling-bullet". It is also known as the shepherd's sling or slingshot (in British English). Someone who specializes in using slings is called a slinger. A sling has a small cradle or ''pouch'' in the middle of two retention cords. A projectile is placed in the pouch. There is a loop on the end of one side of the retention cords. Depending on the design of the sling, either the middle finger or the wrist is placed through a loop on the end of one cord, and a tab at the end of the other cord is placed between the thumb and forefinger. The sling is swung in an arc, and the tab released at a precise moment. This action releases the projectile to fly to the target. The sling is much more than merely an extension of a human arm. By its double-pendulum kinetics, the sling enables stones (or spears) to be thrown much further than they could be by hand alone. The sling is i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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