1990
A skipping rope (British English) or jump rope (American English) is a tool used in the sport of skipping/jump rope where one or more participants jump over a rope swung so that it passes under their feet and over their heads. There are multiple subsets of skipping/jump rope, including single freestyle, single speed, pairs, three-person speed (Double Dutch), and three-person freestyle (Double Dutch freestyle).There are a few major organizations that support jump rope as a sport. Often separated by sex and age, events include hundreds of competitive teams all around the world. In the US, schools rarely have jump rope teams, and states do have sanction official events for elementary school. In freestyle events, jumpers use a variety of basic and advanced techniques in a routine of one minute, which is judged by a head judge, content judges, and performance judges. In speed events, a jumper alternates their feet with the rope going around the jumper every time one of their feet hits the ground for 30 seconds, one minute, or three minutes. The jumper is judged on the number of times the right foot touches the ground in those times.In the Philippines, about 180,000 fourth graders and teachers from at least 3,600 schools nationwide were chosen as beneficiaries of jump ropes through the joint project of the energy drink company, Department of Education (DepEd), and Philippine Jump Rope Association (PJRA).The Jump Rope for the Public School System project aims to complement with physical fitness by introducing children to home-based sports such as Jumping Rope. (Source : Philippine News Agency)Contents
History
1800 illustration of a woman with a skipping ropeExplorers reported seeing aborigines jumping with vines in the 16th century. European boys started skipping in the early 17th century. The activity was considered indecent for girls because they might show their ankles. Girls began skipping in the 18th century,adding skipping chants, owning the rope, controlling the game, and deciding who may participate.In the United States, domination of the activity by girls occurred when their families moved into the cities in the late 19th century. There, they found sidewalks and other smooth surfaces conducive to skipping, along with a host of contemporaries.
Techniques
There are many techniques that can be used when skipping. These can be used individually or combined in a series to create a routine.
Solo participants
For solo jumping, the participant jumps and swings the rope under their feet. The timing of the swing is matched to the jump. This allows them to jump the rope and establish a rhythm more successfully. This can be contrasted with swinging the rope at the feet and jumping, which would mean they were matching the jump to the swing. This makes it harder to jump the rope and establish a rhythm. Basic jump techniqueAlternate foot jump techniqueCriss-cross techniqueLeg over technique
Basic jump or easy jump
Jump with both feet slightly apart over the rope. Beginners usually master this technique first before moving onto more advanced techniques.
Alternate foot jump (speed step)
Use alternate feet to jump off the ground. This technique can be used to effectively double the number of jumps per minute as compared to the above technique. This step can be used for speed events.
Criss-cross
Also known as crossover or cross arms. Perform the basic jump whilst crossing arms in front of the body.Side swing
The rope is passed by the side of the participant's body without jumping it.EB (front-back cross or sailor)
Perform the criss-cross whilst crossing one arm behind the back.
Double under
A high basic jump, turning the rope twice under the feet. Turning the rope three times is called a triple under. In competitions, participants may attempt quadruple (quads) and quintuple under (quins) using the same method.
Boxer jump
One foot is positioned slightly forward and one foot slightly back. The person positions their bodyweight primarily over their front foot, with the back foot acting as a stabiliser. From this stance, the person jumps up several times (often 2-3 times) before switching their stance, so the front foot becomes the back foot, and the back foot becomes the front foot. And so forth. An advantage of this technique is that it allows the back leg a brief rest. So while both feet are still used in the jump, a person may find they can skip for longer than if they were using the basic two-footed technique.
Toad
Perform the criss-cross with one arm crossing under the opposite leg from the inside.Leg over / Crougar
A basic jump with one arm hooked under the adjacent leg.
Awesome Annie
Also known as Awesome Anna or swish. Alternates between a leg over and a toad without a jump in between.Inverse toad
Perform the toad whilst one arm crosses the adjacent leg from the outside.
Elephant
A cross between the inverse toad and the toad, with both arms crossing under one leg.
Frog or Donkey kick
The participant does a handstand, returns to their feet, and turns the rope under them. A more advanced version turns the rope during the return to the ground.
TJ
A triple-under where the first 'jump' is a side swing, the middle jump is a toad and the final jump in the open.Competition techniques[edit]Advanced competition techniqueDouble Dutch - Competition during a steel beach picnic on the ship USS Saipan (LHA-2)In competitions, participants are required to demonstrate competence using specific techniques. The selection depends on the judging system and the country in which the tournament is held.[citation needed]Health effects[edit]Skipping may be used as a cardiovascular workout, similar to jogging or bicycle riding, and has a high MET or intensity level. This aerobic exercise can achieve a "burn rate" of up to 700 to over 1,200 calories per hour of vigorous activity, with about 0.1 to nearly 1.1 calories consumed per jump, mainly depending upon the speed and intensity of jumps and leg foldings.[citation needed] Ten minutes of skipping are roughly the equivalent of running an eight-minute mile. Skipping for 15–20 minutes is enough to burn off the calories from a candy bar and is equivalent to 45–60 minutes of running, depending upon the intensity of jumps and leg swings. Many professional trainers, fitness experts, and professional fighters greatly recommend skipping for burning fat over any other alternative exercises like running and jogging.Weighted skipping ropes are available for such athletes to increase the difficulty and effectiveness of such exercise. Individuals or groups can participate in the exercise, and learning proper techniques is relatively simple compared to many other athletic activities. The exercise is also appropriate for a wide range of ages and fitness levels.Skipping grew in popularity in 2020 when gyms closed or people stayed home due to coronavirus restrictions across the world.These workouts can be done at home and do not require specialized equipment.
Competition
International
There are two main world organizations: International Rope Skipping Federation (FISAC-IRSF), and the World Jump Rope Federation (WJRF). There have been 11 World Championships on every alternate year by (FISAC), with the most recent held in Shanghai, China. There have been 7 World Jump Rope Championships held every year by (WJRF); the most recent taking place in Orlando, Florida. Other locations of this championship include Washington DC, France, and Portugal.In 2018 the International Rope Skipping Federation (FISAC-IRSF) and World Jump Rope Federation (WJRF) announced a merged organization called International Jump Rope Union. The International Jump Rope Union (IJRU) has become the 10th International Federation to gain GAISF Observer status. The decision was taken by the Global Association of International Sports Federations (GAISF) Council, which met during SportAccord in Bangkok. Observer status is the first step on a clear pathway for new International Federations towards the top of the Olympic Family pyramid. Those who wish to proceed will be assisted by GAISF, leading them into full GAISF membership through the Alliance of Independent Recognised Members of Sport (AIMS), and the Association of IOC Recognised International Sports Federations (ARISF).In 2019 the International Rope Skipping Organisations IRSO re-emerged and reactivated its activities. The organization is headed by the founder of Rope Skipping / Jump Rope sport Richard Cendali.
IRSO disagree and was not happy the way both organizations International Rope Skipping Federation and World Jump Rope Federation ignored several long-standing organizations in this merger. Various organizations that have long-standing for the development of the sport but eft out of the merger came under IRSO under the leadership of Richard Cendali. USA Jump Rope Federation and newly formed Asian Rope Skipping Association also joined IRSO and decided to host their World Championship in conjunction with AAU.
World Inter School
The first World Inter-School Rope Skipping Championship was held at Dubai, November 2015.
The second World Inter-School Rope Skipping Championship was held at Eger, Hungary. The Championship was organized by World Inter School Rope Skipping Organisation (WIRSO).Second, third and fourth
World Inter-School championships held in Hungary 2017, Hong Kong 2018 and Belgium 2019 respectively.
March 16, 2022
October 12, 2006
The sphericity of the Earth was established by Greek astronomy in the 3rd century BC, and the earliest terrestrial globe appeared from that period. The earliest known example is the one constructed by Crates of Mallus in Cilicia(now Çukurova in modern-day Turkey), in the mid-2nd century BC.No terrestrial globes from Antiquity have survived. An example of a surviving celestial globe is part of a Hellenistic sculpture, called the Farnese Atlas, surviving in a 2nd-century AD Roman copy in the Naples Archaeological Museum, Italy.Early terrestrial globes depicting the entirety of the Old World were constructed in the Islamic world.During the Middle Ages in Christian Europe, while there are writings alluding to the idea that the earth was spherical, no known attempts at making a globe took place before the fifteenth century.The earliest extant terrestrial globe was made in 1492 by Martin Behaim (1459–1537) with help from the painter Georg Glockendon.Behaim was a German mapmaker, navigator, and merchant. Working in Nuremberg, Germany, he called his globe the "Nürnberg Terrestrial Globe." It is now known as the Erdapfel. Before constructing the globe, Behaim had traveled extensively. He sojourned in Lisbon from 1480, developing commercial interests and mingling with explorers and scientists. He began to construct his globe after his return to Nürnberg in 1490.China made many mapping advancements such as sophisticated land surveys and the invention of the magnetic compass. However, no record of terrestrial globes in China exists until a globe was introduced by the Persian astronomer, Jamal ad-Din, in 1276.Another early globe, the Hunt–Lenox Globe, ca. 1510, is thought to be the source of the phrase Hic Sunt Dracones, or “Here be dragons”. A similar grapefruit-sized globe made from two halves of an ostrich egg was found in 2012 and is believed to date from 1504. It may be the oldest globe to show the New World. Stefaan Missine, who analyzed the globe for the Washington Map Society journal Portolan, said it was “part of an important European collection for decades.” After a year of research in which he consulted many experts, Missine concluded the Hunt–Lenox Globe was a copper cast of the egg globe.A facsimile globe showing America was made by Martin Waldseemueller in 1507. Another "remarkably modern-looking" terrestrial globe of the Earth was constructed by Taqi al-Din at the Constantinople Observatory of Taqi ad-Din during the 1570s.The world's first seamless celestial globe was built by Mughal scientists under the patronage of Jahangir.Globus IMP, electro-mechanical devices including five-inch globes have been used in Soviet and Russian spacecraft from 1961 to 2002 as navigation instruments. In 2001, the TMA version of the Soyuz spacecraft replaced this instrument with a digital map.
March 16, 2022
1492
A hair dryer, hairdryer or blow dryer is an electromechanical device that blows ambient or hot air over damp hair to speed the evaporation of water to dry the hair. Blow dryers enable better control over the shape and style of hair, by accelerating and controlling the formation of temporary hydrogen bonds within each strand. These bonds are powerful (allowing stronger hair shaping than the sulfur bonds formed by permanent waving products) but are temporary and extremely vulnerable to humidity. They disappear with a single washing of the hair.The normal use of a hair dryerHairstyles using blow dryers usually have volume and discipline, which can be further improved with styling products, hairbrushes, and combs during drying to add tension, hold and lift.Blow dryers were invented in the late 19th century. The first, stationary, model was created by Alexander F. Godefroy in his salon in France. The handheld, household hair dryer first appeared in 1920. Blow dryers are used in beauty salons by professional stylists and in the household by consumers.
1920
Zinedine Yazid Zidane was born on June 23, 1972, in Marseille, France. The son of Algerian immigrants, Zidane learned to play soccer in the streets of La Castellane, a rough section of Marseille. After starring for local youth clubs, 14-year-old Zidane was discovered at a French Football Federation training camp by AS Cannes recruiter Jean Varraud, and spent the next three years honing his skills in Cannes' youth division.
Zidane made his first professional appearance for Cannes at 17, scoring a goal in his debut. He transferred to Bordeaux in 1992, and in ensuing years the attacking midfielder earned renown for his sterling all-around play. Prone to the occasional flash of temper, Zidane otherwise was the embodiment of control with the ball at his feet, seemingly knowing when to maneuver through the defense, find a teammate with a pinpoint pass or rocket a shot at the goal.
Zidane transferred to Juventus F.C. in Italy's prestigious Series A League in 1996. The move brought a marked increase in visibility and expectations, but Zidane proved he was up to the challenge by steering Juventus to an Italian Super Cup, a UEFA Super Cup, an Intercontinental Cup and a pair of Series A titles over the next two seasons.At his peak when France hosted the 1998 World Cup, Zidane spearheaded Les Bleus' march through the tournament with his crisp passing and dribbling, and then scored twice as France shut down Brazil in the final, 3-0, to become a national hero. Two years later, Zidane again was the linchpin of the French team's run to international glory, which culminated with a 2-1 win over Italy for the European Championship.In 2001, Zidane signed with Spanish club Real Madrid for a world-record transfer fee of more than $66 million. The investment paid immediate dividends, as the French import helped Real Madrid win the coveted UEFA Champions League title in his first year and La Liga the following season.
Zidane had indicated he would retire after the 2006 World Cup in Germany, and it appeared his career was heading for a storybook finish when France advanced to the final against Italy. Instead, it ended in shocking fashion when, enraged by opponent Marco Materazzi's comments to him in extra time, he slammed his head into the Italian player's chest. Zidane was thrown out of the game, and France subsequently lost on penalty kicks.
Zidane joined Real Madrid's front office as an adviser and was named the club's sporting director in 2011. The following year, it was announced the French soccer legend would begin coaching at Real Madrid's youth academy, and in 2014 he was named coach of the club's B team.In January 2016, Zidane took over as manager of Real Madrid's first team. While some doubted how he would fare in front of a demanding owner and fan base, the icon soon silenced the critics with his overwhelming success, becoming the first manager to win two and then three consecutive Champions League titles. He also led Real Madrid to two UEFA Super Cups, two FIFA World Club Cups, one Spanish title and one Spanish Super Cup, before announcing he was stepping down in May 2018.However, Zidane was gone from the post for less than a year, as he returned to manage Real Madrid in March 2019.
In 2004, Zidane was named best European soccer player of the past 50 years by the UEFA Golden Jubilee Poll and was included in the FIFA 100, Pelé's list of the 125 greatest living players. He remains one of a handful of greats to win the FIFA World Player of the Year/Ballon d'Or award three times.
1972
Professional association football team based in manchester, england
One of the basic pieces of furniture, a chair is a type of seat. Its primary features are two pieces of a durable material, attached as back and seat to one another at a 90°-or-slightly-greater angle, with usually the four corners of the horizontal seat attached in turn to four legs—or other parts of the seat's underside attached to three legs or to a shaft about which a four-arm turnstile on rollers can turn—strong enough to support the weight of a person who sits on the seat (usually wide and broad enough to hold the lower body from the buttocks almost to the knees) and leans against the vertical back (usually high and wide enough to support the back to the shoulder blades). The legs are typically high enough for the seated person's thighs and knees to form a 90°-or-lesser angle. Used in a number of rooms in homes (e.g. in living rooms, dining rooms, and dens), in schools and offices (with desks), and in various other workplaces, chairs may be made of wood, metal, or synthetic materials, and either the seat alone or the entire chair may be padded or upholstered in various colors and fabrics.Chairs vary in design. An armchair has armrests fixed to the seat;a recliner is upholstered and under its seat is a mechanism that allows one to lower the chair's back and raise into place a fold-out footrest; a rocking chair has legs fixed to two long curved slats; and a wheelchair has wheels fixed to an axis under the seat.
HistoryMain article: History of the chairThe Coronation Chair, circa 1300The Monobloc chair is a lightweight stackable polypropylenechair, usually white in colour, often described as the world's most common plastic chair.The chair has been used since antiquity, although for many centuries it was a symbolic article of state and dignity rather than an article for ordinary use. "The chair" is still used as the emblem of authority in the House of Commons in the United Kingdom and Canada, and in many other settings. In keeping with this historical connotation of the "chair" as the symbol of authority, committees, boards of directors, and academic departments all have a 'chairman' or 'chair'.Endowed professorships are referred to as chairs. It was not until the 16th century that chairs became common. Until then, people sat on chests, benches, and stools, which were the ordinary seats of everyday life. The number of chairs which have survived from an earlier date is exceedingly limited; most examples are of ecclesiastical, seigneurial or feudal origin.[citation needed]Chairs were in existence since at least the Early Dynastic Period of Egypt (c. 3100 BC). They were covered with cloth or leather, were made of carved wood, and were much lower than today's chairs – chair seats were sometimes only 10 inches (25 cm) high.In ancient Egypt chairs appear to have been of great richness and splendor. Fashioned of ebony and ivory, or of carved and gilded wood, they were covered with costly materials, magnificent patterns and supported upon representations of the legs of beasts or the figures of captives. Generally speaking, the higher ranked an individual was, the taller and more sumptuous was the chair he sat on and the greater the honor. On state occasions the pharaoh sat on a throne, often with a little footstool in front of it.The average Egyptian family seldom had chairs, and if they did, it was usually only the master of the household who sat on a chair. Among the better off, the chairs might be painted to look like the ornate inlaid and carved chairs of the rich, but the craftsmanship was usually poor.The earliest images of chairs in China are from 6th-century Buddhist murals and stele, but the practice of sitting in chairs at that time was rare. It was not until the 12th century that chairs became widespread in China. Scholars disagree on the reasons for the adoption of the chair. The most common theories are that the chair was an outgrowth of indigenous Chinese furniture, that it evolved from a camp stool imported from Central Asia, that it was introduced to China by Christian missionaries in the 7th century, and that the chair came to China from India as a form of Buddhist monastic furniture. In modern China, unlike Koreaor Japan, it is no longer common to sit at floor level.In Europe, it was owing in great measure to the Renaissance that the chair ceased to be a privilege of state and became a standard item of furniture for anyone who could afford to buy it. Once the idea of privilege faded the chair speedily came into general use. Almost at once the chair began to change every few years to reflect the fashions of the day.Thomas Edward Bowdich visited the main Palace of the Ashanti Empire in 1819, and observed chairs engrossed with gold in the empire. In the 1880s, chairs became more common in American households and usually there was a chair provided for every family member to sit down to dinner. By the 1830s, factory-manufactured “fancy chairs” like those by Sears. Roebuck, and Co. allowed families to purchase machined sets. With the Industrial Revolution, chairs became much more available.The 20th century saw an increasing use of technology in chair construction with such things as all-metal folding chairs, metal-legged chairs, the Slumber Chair,[citation needed] moulded plastic chairs and ergonomic chairs. The recliner became a popular form, at least in part due to radio and television.The modern movement of the 1960s produced new forms of chairs: the butterfly chair (originally called the Hardoy chair), bean bags, and the egg-shaped pod chair that turns. It also introduced the first mass-produced plastic chairs such as the Bofinger chair in 1966. Technological advances led to molded plywoodand wood laminate chairs, as well as chairs made of leather or polymers. Mechanical technology incorporated into the chair enabled adjustable chairs, especially for office use. Motors embedded in the chair resulted in massage chairs.
Air conditioning, often abbreviated as A/C or AC, is the process of removing heat and controlling the humidity of air in an enclosed space to achieve a more comfortable interior environment by use of powered "air conditioners" or a variety of other methods, including passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning (HVAC).Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used within vehicles or single rooms to massive units that can cool large buildings.Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates.According to the International Energy Agency (IEA), as of 2018, 1.6 billion air conditioning units were installed, which accounted for an estimated 20% of energy usage in buildings globally with the number expected to grow to 5.6 billion by 2050. The United Nations called for the technology to be made more sustainable to mitigate climate change using techniques including passive cooling, evaporative cooling, selective shading, windcatchers and better thermal insulation. CFC and HCFC refrigerants such as R-12 and R-22, respectively, used within air conditioners have caused damage to the ozone layer, and HFC refrigerants such as R-410a and R-404a, which were designed to replace CFCs and HCFCs, are instead exacerbating climate change. Both issues happen due to venting of refrigerant to the atmosphere, such as during repairs. HFO refrigerants, used in some if not most new equipment, solve both issues with an ozone damage potential (ODP) of zero and a much lower global warming potential (GWP) in the single or double digits vs. the three or four digits of HFCs.
History Air-conditioning dates back to prehistory. Ancient Egyptian buildings used a wide variety of passive air-conditioning techniques.These became widespread from the Iberian Peninsula through North Africa, the Middle East, and Northern India. Similar techniques were developed in hot climates elsewhere.[further explanation needed]Passive techniques remained widespread until the 20th century, when they fell out of fashion, replaced by powered A/C. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs.An array of air conditioners outside a commercial office buildingAir conditioners allow the building indoor environment to remain relatively constant largely independent of changes in external weather conditions and internal heat loads. They also allow deep plan buildings to be created and have allowed people to live comfortably in hotter parts of the world.
Development
Preceding discoveries
In 1558, Giambattista della Porta described a method of chilling ice to temperatures far below its freezing point by mixing it with potassium nitrate (then called "nitre") in his popular science book Natural Magic.[7][8][9] In 1620, Cornelis Drebbel demonstrated "Turning Summer into Winter" for James I of England, chilling part of the Great Hall of Westminster Abbey with an apparatus of troughs and vats. Drebbel's contemporary Francis Bacon, like della Porta a believer in science communication, may not have been present at the demonstration, but in a book published later the same year, he described it as "experiment of artificial freezing" and said that "Nitre (or rather its spirit) is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its own cold, but the salt by supplying activity to the cold of the snow."In 1758, Benjamin Franklin and John Hadley, a chemistry professor at University of Cambridge, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that the evaporation of highly volatile liquids (such as alcohol and ether) could be used to drive down the temperature of an object past the freezing point of water. They conducted their experiment with the bulb of a mercury-in-glass thermometer as their object and with a bellows used to speed up the evaporation. They lowered the temperature of the thermometer bulb down to −14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). Franklin noted that soon after they passed the freezing point of water 0 °C (32 °F), a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm (1⁄4 in) thick when they stopped the experiment upon reaching −14 °C (7 °F). Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."The 19th century included a number of developments in compression technology. In 1820, English scientist and inventor Michael Faraday discovered that compressing and liquefying ammoniacould chill air when the liquefied ammonia was allowed to evaporate.[12] In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped to eventually use his ice-making machine to regulate the temperature of buildings and envisioned centralized air conditioning that could cool entire cities. Gorrie was granted a patent in 1851, but following the death of his main backer he was not able to realise his invention.In 1851, James Harrison created the first mechanical ice-making machine in Geelong, Australia, and was granted a patent for an ether vapor-compression refrigeration system in 1855 that produced three tons of ice per day.In 1860, Harrison established a second ice company and later entered the debate over how to compete against the American advantage of ice-refrigerated beef sales to the United Kingdom.
First A/C devices
Willis Carrier, who is credited with building the first modern electrical air conditioning unitElectricity made development of effective units possible. In 1901, American inventor Willis H. Carrier built what is considered the first modern electrical air conditioning unit. In 1902, he installed his first air-conditioning system, in the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, New York; his invention controlled both the temperature and also the humidity which helped maintain consistent paper dimensions and ink alignment at the printing plant. Later, together with six other employees, Carrier formed The Carrier Air Conditioning Company of America, a business that in 2020 employed 53,000 employees and was valued at $18.6 billion.In 1906, Stuart W. Cramer of Charlotte, North Carolina was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning," using it in a patent claim he filed that year as analogous to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.[23]Domestic air conditioning soon took off. In 1914, the first domestic air conditioning was installed in Minneapolis in the home of Charles Gilbert Gates. It is however possible that the huge device (c. 7 x 6 x 20 ft) was never used, as the house remained uninhabited (Gates had already died in October 1913).In 1931, H.H. Schultz and J.Q. Sherman developed what would become the most common type of individual room air conditioner: one designed to sit on a window ledge. The units went on sale in 1932 at a considerable price (the equivalent of $120,000 to $600,000 in today's money.)[12] A year later the first air conditioning systems for cars were offered for sale.Chrysler Motors introduced the first practical semi-portable air conditioning unit in 1935,and Packard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939.
Further development
Types of air conditioner
Mini-split and multi-split systems
Evaporator, indoor unit, or terminal, side of a ductless split-type air conditionerDuctless systems (often mini-split, though there are now ducted mini split) typically supply conditioned and heated air to a single or a few rooms of a building, without ducts and in a decentralized manner. Multi-zone or multi-split systems are a common application of ductless systems and allow up to eight rooms (zones or locations) to be conditioned independently from each other, each with its own indoor unit and simultaneously from a single outdoor unit. The main problem with multi-split systems is the length of the refrigerant lines for connecting the external unit to the internal ones.[citation needed] Though the same challenge exists for central ACs.The first mini-split systems were sold in 1954–1968 by Mitsubishi Electric and Toshiba in Japan, where its development was motivated by the small size of homes.[35][36][37] Multi-zone ductless systems were invented by Daikin in 1973, and variable refrigerant flow systems (which can be thought of as larger multi-split systems) were also invented by Daikin in 1982. Both were first sold in Japan.Variable refrigerant flow systems when compared with central plant cooling from an air handler, eliminate the need for large cool air ducts, air handlers, and chillers; instead cool refrigerant is transported through much smaller pipes to the indoor units in the spaces to be conditioned, thus allowing for less space above dropped ceilings and a lower structural impact, while also allowing for more individual and independent temperature control of spaces, and the outdoor and indoor units can be spread across the building. Variable refrigerant flow indoor units can also be turned off individually in unused spaces.
Ducted central systems
Split-system central air conditioners consist of two heat exchangers, an outside unit (the condenser) from which heat is rejected to the environment and an internal heat exchanger (the fan coil unit, air handling unit, or evaporator) with the piped refrigerant being circulated between the two. The FCU is then connected to the spaces to be cooled by ventilation ducts.
Central plant cooling
See also: ChillerAn industrial air conditioning unit on top of the shopping mall Passage in Linz, Austria.Large central cooling plants may use intermediate coolant such as chilled water pumped into air handlers or fan coil units near or in the spaces to be cooled which then duct or deliver cold air into the spaces to be conditioned, rather than ducting cold air directly to these spaces from the plant, which is not done due to the low density and heat capacity of air which would require impractically large ducts. The chilled water is cooled by chillers in the plant, which use a refrigeration cycle to cool water, often transferring its heat to the atmosphere even in liquid-cooled chillers through the use of cooling towers. Chillers may be air or liquid-cooled.
Portable units
A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit (such as a central air conditioner).[citation needed]Hose systems, which can be monoblock or air-to-air, are vented to the outside via air ducts. The monoblock type collects the water in a bucket or tray and stops when full. The air-to-air type re-evaporates the water and discharges it through the ducted hose and can run continuously. Such portable units draw indoor air and expel it outdoors through a single duct.Many portable air conditioners come with heat as well as dehumidification function.Window unit and packaged terminal
Main article:
Packaged terminal air conditionerThe packaged terminal air conditioner (PTAC), through-the-wall, and window air conditioners are similar. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heaters, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump. They may be installed in a wall opening with the help of a special sleeve on the wall and a custom grill that is flush with the wall and window air conditioners can also be installed in a window, but without a custom grill.
Packaged air conditioner
Packaged air conditioners (also known as self-contained units) are central systems that integrate into a single housing all the components of a split central system, and deliver air, possibly through ducts, to the spaces to be cooled. Depending on their construction they may be outdoors or indoors, on roofs (rooftop units),draw the air to be conditioned from inside or outside a building and be water, refrigerant or air-cooled. Often, outdoor units are air-cooled while indoor units are liquid-cooled using a cooling tower.
Operation
Operating principles
Main article: Vapor-compression refrigerationA simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressorCooling in traditional AC systems is accomplished using the vapor-compression cycle, which uses the forced circulation and phase change of a refrigerant between gas and liquid to transfer heat. The vapor-compression cycle can occur within a unitary, or packaged piece of equipment; or within a chiller that is connected to terminal cooling equipment (such as a fan coil unit in an air handler) on its evaporator side and heat rejection equipment such as a cooling tower on its condenser side. An air source heat pump shares many components with an air conditioning system, but includes a reversing valve which allows the unit to be used to heat as well as cool a space.Air conditioning equipment will reduce the absolute humidity of the air processed by the system if the surface of the evaporator coil is significantly cooler than the dew point of the surrounding air. An air conditioner designed for an occupied space will typically achieve a 30% to 60% relative humidity in the occupied space.Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed to reduce the evaporator temperature and therefore condense more water. A dehumidifier uses the same refrigeration cycle but incorporates both the evaporator and the condenser into the same air path; the air first passes over the evaporator coil where it is cooled and dehumidified before passes over the condenser coil where it is warmed again before being released back into the room again.[citation needed]Free cooling can sometimes be selected when the external air happens to be cooler than the internal air and therefore the compressor needs not be used, resulting in high cooling efficiencies for these times. This may also be combined with seasonal thermal energy storage.
Heating
Main article: Heat pumpSome air conditioning systems have the option to reverse the refrigeration cycle and act as air source heat pump, therefore producing heating instead of cooling in the indoor environment. They are also commonly referred to as "reverse cycle air conditioners". The heat pump is significantly more energy efficient than electric resistance heating, because it moves energy from air or groundwater to the heated space, as well as the heat from purchased electrical energy. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator and discharges cold air (colder than the ambient outdoor air).Air-source heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 4–13 °C (40–55 °F), because heat pumps become inefficient in more extreme cold. This is partly because ice forms on the outdoor unit's heat exchanger coil, which blocks airflow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil back to being the condenser coil, so that it can heat up and defrost. Some heat pump systems will therefore have a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary indoor air cooling, which would otherwise be uncomfortable in the winter.The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as an electrical heater, a natural gas, Heating oil or wood-burning fireplace or central heating, which is used instead of the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during the milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.
Performance
Main articles: coefficient of performance, Seasonal energy efficiency ratio, and European seasonal energy efficiency ratioThe coefficient of performance (COP) of a air conditioning system is a ratio of useful heating or cooling provided to work required. Higher COPs equate to lower operating costs. The COP usually exceeds 1; however, the exact value is highly dependent on operating conditions, especially absolute temperature and relative temperature between sink and system, and is often graphed or averaged against expected conditions.Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration," with each approximately equal to the cooling power of one short ton (2,000 pounds (910 kg) of ice melting in a 24-hour period. The value is equal to 12,000 BTUIT per hour, or 3,517 watts. Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.[citation needed]The efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. A similar standard is the European seasonal energy efficiency ratio (ESEER).
Impact
Health effects
In hot weather, air conditioning can prevent heat stroke, dehydration from excessive perspiration, and other problems related to hyperthermia. Heat waves are the most lethal type of weather phenomenon in developed countries. Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people with allergies, especially mold.[citation needed]Poorly maintained water cooling towers can promote the growth and spread of microorganisms such as Legionella pneumophila, the infectious agent responsible for Legionnaires' disease. As long as the cooling tower is kept clean (usually by means of a chlorine treatment), these health hazards can be avoided or reduced. The state of New York has codified requirements for registration, maintenance, and testing of cooling towers to protect against Legionella.
Environmental impacts
Refrigerants have caused and continue to cause serious environmental issues, including ozone depletion and climate change, as several countries have not yet ratified the Kigali Amendment to reduce the consumption and production of hydrofluorocarbons.Current air conditioning accounts for 20% of energy consumption in buildings globally, and the expected growth of the usage of air conditioning due to climate change and technology uptake will drive significant energy demand growth. Alternatives to continual air conditioning include passive cooling, passive solar cooling natural ventilation, operating shades to reduce solar gain, using trees, architectural shades, windows (and using window coatings) to reduce solar gain.In 2018 the United Nations called for the technology to be made more sustainable to mitigate climate change.
Economic effects
Air conditioning caused various shifts in demography, notably that of the United States starting from the 1970s:The birth rate was lower in the spring than during other seasons until 1970s but this difference then declined over the next 30 years.The summer mortality rate, which had been higher in regions subject to a heatwave during the summer, also evened out.The Sun Belt now contains 30% of the total US population when it was inhabited by 24% of Americans at the beginning of the 20th century.First designed to benefit targeted industries such as the press as well as large factories, the invention quickly spread to public agencies and administrations with studies with claims of increased productivity close to 24% in places equipped with air conditioning.
Other techniques
Buildings designed with passive air conditioning are generally less expensive to construct and maintain than buildings with conventional HVAC systems with lower energy demands.While tens of air changes per hour, and cooling of tens of degrees, can be achieved with passive methods, site-specific microclimate must be taken into account, complicating building design.Many techniques can be used to increase comfort and reduce the temperature in buildings. These include evaporative cooling, selective shading, wind, thermal convection, and heat storage.
Passive ventilation
This section is an excerpt from Passive ventilation.The ventilation system of a regular earthship.Dogtrot houses are designed to maximise natural ventilation.Passive ventilation is the process of supplying air to and removing air from an indoor space without using mechanical systems. It refers to the flow of external air to an indoor space as a result of pressure differences arising from natural forces. There are two types of natural ventilation occurring in buildings: wind driven ventilation and buoyancy-driven ventilation. Wind driven ventilation arises from the different pressures created by wind around a building or structure, and openings being formed on the perimeter which then permit flow through the building. Buoyancy-driven ventilation occurs as a result of the directional buoyancy force that results from temperature differences between the interior and exterior.Since the internal heat gains which create temperature differences between the interior and exterior are created by natural processes, including the heat from people, and wind effects are variable, naturally ventilated buildings are sometimes called "breathing buildings".
Passive cooling
This section is an excerpt from Passive cooling.
A traditional Iranian solar cooling design using a wind towerPassive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption.This approach works either by preventing heat from entering the interior (heat gain prevention) or by removing heat from the building (natural cooling).Natural cooling utilizes on-site energy, available from the natural environment, combined with the architectural design of building components (e.g. building envelope), rather than mechanical systems to dissipate heat. Therefore, natural cooling depends not only on the architectural design of the building but on how the site's natural resources are used as heat sinks (i.e. everything that absorbs or dissipates heat). Examples of on-site heat sinks are the upper atmosphere (night sky), the outdoor air (wind), and the earth/soil.
Passive cooling is an important tool for design of buildings for climate change adaptation – reducing dependency on energy-intensive air conditioning in warming environments.A pair of short windcatchers or malqaf used in traditional architecture; wind is forced down on the windward side and leaves on the leeward side (cross-ventilation). In the absence of wind, the circulation can be driven with evaporative cooling in the inlet (which is also designed to catch dust). In the center, a shuksheika (roof lantern vent), used to shade the qa'a below while allowing hot air rise out of it (stack effect).
Fans
Main article: Ceiling fanHand fans have existed since prehistory. Large human-powered fans built into buildings include the punkah.The 2nd-century Chinese inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered by prisoners.: 99, 151, 233 In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the Cool Hall (Liang Dian 涼殿) built in the imperial palace, which the Tang Yulin describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.: 134, 151
Thermal buffering
In areas which are cold at night or in winter, heat storage is used. Heat may be stored in earth or masonry; air is drawn past the masonry to heat or cool it.In areas which are below freezing at night in winter, snow and ice can be collected and stored in ice houses for later use in cooling.This technique is over 3,700 years old in the Middle East.Harvesting outdoor ice during winter and transporting and storing for use in summer was practiced by wealthy Europeans in the early 1600s, and became popular in Europe and the Americas towards the end of the 1600s This practice was replaced by mechanical compression-cycle ice-making machines (see below).
Evaporative cooling.
Main article: Evaporative coolerAn evaporative coolerIn dry, hot climates, the evaporative cooling effect may be used by placing water at the air intake, such that the draft draws air over water and then into the house. For this reason, it is sometimes said that the fountain, in the architecture of hot, arid climates, is like the fireplace in the architecture of cold climates.Evaporative cooling also makes the air more humid, which can be beneficial in a dry desert climate.Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window.
Lightning
Lightning is an electrical spark discharge in the atmosphere that occurs during a thunderstorm, manifested by a bright flash of light and accompanying thunder. Lightning has also been recorded on Venus, Jupiter, Saturn, Uranus, etc. Current intensity in the lightning discharge on the Earth reaches 10-500 thousand amperes, voltage - from tens of millions to billions of volts.
The longest lightning was recorded in 2020 on the border of Mississippi and Texas, its length was 768 km. The longest lightning was recorded in Argentina, its duration was 17.1 seconds. The record high potential difference during a thunderstorm of 1.3 GV was recorded in 2014
History of study Lightning 1882 (c) Photographer: William N. Jennings, C. 1882The lightning has been the object of human interest since antiquity. Its dangerous manifestations have been known since ancient times. In paganism, lightning was considered the activity of the most powerful gods: Zeus in Greek mythology, Perun in Slavic mythology. Being struck by lightning was considered a god's punishment. Accordingly, certain rituals and ceremonies were performed to protect against lightning. From antique and Slavic mythology idea of lightning as an instrument of divine activity has passed to Christianity. In spite of perception of lightning as manifestation of supreme forces, nevertheless already in antiquity certain regularities in striking objects by lightning were revealed. Thales already described that lightning most often strikes tall free-standing objects. In the Middle Ages lightning often caused fires in wooden cities, which gave rise to the rule that you can not build houses above the temple. Temples, usually located on high ground, acted as lightning rods in these cases. It was also noticed that metallized (in those years - mostly gilded) domes were less often struck by lightning.A great impulse in the study of lightning was given by the development of seafaring. Firstly, seafarers encountered thunderstorms of unprecedented strength on the land; secondly, they discovered that thunderstorms were unevenly distributed over geographical latitudes; thirdly, they noticed that when lightning struck nearby, the compass arrow experienced strong disturbances; fourthly, they clearly linked the appearance of the lights of Saint Elmo and an approaching thunderstorm. In addition, it was the sailors who first noticed that phenomena similar to those that occur when glass or wool is electrified by friction appeared before a thunderstorm.The development of physics in the XVII-XVIII centuries allowed to put forward a hypothesis about the connection between lightning and electricity. In particular, such a view was held by M. V. Lomonosov. The electrical nature of lightning was disclosed in the studies of American physicist B. Franklin, whose idea was the experiment to extract electricity from a thunderstorm cloud. Franklin's experience in elucidating the electrical nature of lightning is widely known. In 1750 he published a paper describing an experiment using a kite launched into a thunderstorm. By the beginning of the XIX century, most scientists no longer doubted the electrical nature of lightning (although there were alternative hypotheses, for example, chemical) and the main research questions were the mechanism of electricity generation in thunderclouds and the parameters of the lightning discharge.In 1989, were discovered special types of lightning in the upper atmosphere: elves and sprites. In 1995 another type of lightning in the upper atmosphere - jets - was discovered.At the end of the 20th century when studying lightning new physical phenomena were discovered - breakdown on escaping electrons and photonuclear reactions under the influence of gamma-radiation of lightning discharge.To study lightning physics methods of observation from satellites are used.
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Novelette by isaac asimov
A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically malleable (they can be hammered into thin sheets) or ductile (can be drawn into wires). A metal may be a chemical ele...
A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically malleable (they can be hammered into thin sheets) or ductile (can be drawn into wires). A metal may be a chemical ele...
Silver is a chemical element with the symbol Ag (from the Latin argentum, derived from the Proto-Indo-European h₂erǵ: "shiny" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal.The metal is found in the Earth's crust in the pure, free elemental form ("native silver"), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining.Silver has long been valued as a precious metal. Silver metal is used in many bullion coins, sometimes alongside gold: while it is more abundant than gold, it is much less abundant as a native metal. Its purity is typically measured on a per-mille basis; a 94%-pure alloy is described as "0.940 fine". As one of the seven metals of antiquity, silver has had an enduring role in most human cultures.Other than in currency and as an investment medium (coins and bullion), silver is used in solar panels, water filtration, jewellery, ornaments, high-value tableware and utensils (hence the term "silverware"), in electrical contacts and conductors, in specialized mirrors, window coatings, in catalysis of chemical reactions, as a colorant in stained glass, and in specialized confectionery. Its compounds are used in photographic and X-rayfilm. Dilute solutions of silver nitrate and other silver compounds are used as disinfectants and microbiocides (oligodynamic effect), added to bandages, wound-dressings, catheters, and other medical instruments.
A metal (from Greek μέταλλον métallon, "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typically malleable (they can be hammered into thin sheets) or ductile (can be drawn into wires). A metal may be a chemical ele...
Gold is a chemical element with the symbol Au (from Latin: aurum) and atomic number 79, making it one of the higher atomic number elements that occur naturally. In a pure form, it is a bright, slightly orange yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metaland a group 11 element. It is one of the least reactive chemical elements and is solid under standard conditions. Gold often occurs in free elemental (native) form, as nuggets or grains, in rocks, in veins, and in alluvial deposits. It occurs in a solid solution series with the native element silver (as electrum), naturally alloyed with other metals like copper and palladium and also as mineral inclusions such as within pyrite. Less commonly, it occurs in minerals as gold compounds, often with tellurium (gold tellurides).Gold is resistant to most acids, though it does dissolve in aqua regia (a mixture of nitric acid and hydrochloric acid), which forms a soluble tetrachloroaurate anion. Gold is insoluble in nitric acid, which dissolves silver and base metals, a property that has long been used to refine gold and to confirm the presence of gold in metallic substances, giving rise to the term acid test. Gold also dissolves in alkaline solutions of cyanide, which are used in mining and electroplating. Gold dissolves in mercury, forming amalgam alloys, and as the gold acts simply as a solute this is not a chemical reaction.A relatively rare element, gold is a precious metal that has been used for coinage, jewelry, and other arts throughout recorded history. In the past, a gold standard was often implemented as a monetary policy, but gold coins ceased to be minted as a circulating currency in the 1930s, and the world gold standard was abandoned for a fiat currency system after 1971.A total of around 201,296 tonnes of gold exists above ground, as of 2020.This is equal to a cube with each side measuring roughly 21.7 meters (71 ft). The world consumption of new gold produced is about 50% in jewelry, 40% in investments, and 10% in industry.Gold's high malleability, ductility, resistance to corrosion and most other chemical reactions, and conductivity of electricity have led to its continued use in corrosion resistant electrical connectors in all types of computerized devices (its chief industrial use). Gold is also used in infrared shielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. As of 2017, the world's largest gold producer by far was China with 440 tonnes per year.