Many people today have flown in an airplane. It is a common communication network today. To travel long distance airplane is must. Many ask the simple question “what makes an airplane fly”? The answer one frequently gets is misleading and often just plain wrong. We hope that the answers provided here will clarify many misconceptions. We are going to show you that lift is easier to understand if one starts with Newton rather than Bernoulli. We will also show you that the popular explanation that most of us were taught is misleading at best and that lift is due to the wing diverting air down.

For an airplane to fly, it must always engage in a tug of war between the opposing forces of lift versus weight and thrust versus drag.  For a moment, think of an airplane moving from right to left and the flow of air moving from left to right. The weight or force due to gravity pulls down on the plane opposing the lift created by air flowing over the wing. Thrust is generated by the propeller and opposes drag caused by air resistance to the airplane.  During take off, thrust must be greater than drag and lift must be greater than weight so that the airplane can become airborne. For landing thrust must be less than drag, and lift must be less than weight.

An airplane in flight is the center of a continuous tug of war between four forces: lift, gravity force or weight, thrust, and drag. Lift and Drag are considered aerodynamic forces because they exist due to the movement of the aircraft through the air.  The weight pulls down on the plane opposing the lift created by air flowing over the wing. Thrust is generated by the propeller and opposes drag caused by air resistance to the frontal area of the airplane. During take off, thrust must overcome drag and lift must overcome the weight before the airplane can become airborne. In level flight at constant speed, thrust exactly equals drag and lift exactly equals the weight or gravity force. For landings thrust must be reduced below the level of drag and lift below the level of the gravity force or weight.

Lift: Lift is produced by a lower pressure created on the upper surface of an airplane’s wing compared to the pressure on the wing’s lower surface, causing the wing to be “lifted” upward. The special shape of the airplane wing (airfoil) is designed so that air flowing over it will have to travel a greater distance faster, resulting in a lower pressure area (see illustration) thus lifting the wing upward. Lift is that force which opposes the force of gravity (or weight).

Many believe that this explanation is incorrect because flat wings (such as seen on balsa wood airplanes, paper planes and others) also have managed to create lift.   Please read How planes fly:  the physical description of flight as well to get a fuller understanding of the creation of lift.  It is more advanced, though.

Thrust: Thrust is a force created by a power source which gives an airplane forward motion. It can either “pull” or “push” an airplane forward. Thrust is that force which overcomes drag. Conventional airplanes utilize engines as well as propellers to obtain thrust.

Drag : Drag is the force which delays or slows the forward movement of an airplane through the air when the airflow direction is opposite to the direction of motion of the airplane. It is the friction of the air as it meets and passes over and about an airplane and its components. The more surface area exposed to rushing air, the greater the drag. An airplane’s streamlined shape helps it pass through the air more easily.

An Air conditioner is a common electronic device. It used offices and home in everywhere, especially in the tropical region. An air conditioner (often referred to as AC) is a home appliance, system, or mechanism designed to dehumidify and extract heat from an area. The cooling is done using a simple refrigeration cycle. In construction, a complete system of heating, ventilation and air conditioning is referred to as “HVAC”.In 1758, Benjamin Franklin and John Hadley, professor of chemistry at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that 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 thermometer as their object and with a bellows used to “quicken” the evaporation; they lowered the temperature of the thermometer bulb to -14 °C (7 °F) while the ambient temperature was 18 °C (64 °F). In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate.
Air conditioners employ the same operating principles and basic components as your home refrigerator. Refrigerators use energy (usually electricity) to transfer heat from the cool interior of the refrigerator to the relatively warm surroundings of your home; likewise, an air conditioner uses energy to transfer heat from the interior of your home to the relatively warm outside environment.
An air conditioner cools your home with a cold indoor coil called the evaporator. The condenser, a hot outdoor coil, releases the collected heat outside. The evaporator and condenser coils are serpentine tubing surrounded by aluminum fins. This tubing is usually made of copper.
A pump, called the compressor, moves a heat transfer fluid (or refrigerant) between the evaporator and the condenser. The pump forces the refrigerant through the circuit of tubing and fins in the coils.
The liquid refrigerant evaporates in the indoor evaporator coil, pulling heat out of indoor air and thereby cooling your home. The hot refrigerant gas is pumped outdoors into the condenser where it reverts back to a liquid, giving up its heat to the outside air flowing over the condenser’s metal tubing and fins.
Throughout the second half of the 20th century, nearly all air conditioners used chlorofluorocarbons (CFCs) as their refrigerant, but because these chemicals are damaging to Earth’s ozone layer, CFC production stopped in the United States in 1995. Nearly all air conditioning systems now employ halogenated chlorofluorocarbons (HCFCs) as a refrigerant, but these are also being gradually phased out, with most production and importing stopped by 2020 and all production and importing stopped by 2030.
Production and importing of today’s main refrigerant for home air conditioners, HCFC-22 (also called R-22), has begin to be phased out in 2010 and will stop entirely by 2020. However, HCFC-22 is expected to be available for many years as it is recovered from old systems that are taken out of service.

Paper is a thin material mainly used for writing option, printing upon or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses and drying them into flexible sheets. Paper is a versatile material with many uses. Whilst the most common is for writing and printing upon, it is also widely used as a packaging material, in many cleaning products, in a number of industrial and construction processes, and occasionally as a food ingredient, particularly in Asian cultures. The word paper derives from the Greek term for the ancient Egyptian writing material called papyrus, which was formed from beaten stripes of papyrus plants.

Paper is chiefly used for written communication. The earliest paper was papyrus, made from reeds by the ancient Egyptians. Paper was made by the Chinese in the second century, probably by a Chinese court official named Cai Lun. His paper was made from such things as tree bark and old fish netting. Recognized almost immediately as a valuable secret, it was 500 years before the Japanese acquired knowledge of the method. Papermaking was known in the Islamic world from the end of eight century A.D.

Knowledge of papermaking eventually moved westward, and the first European paper mill was built at Jativa, in the province of Valencia, Spain, in about 1150. By the end of the 15^th century, paper mills existed in Italy, France, Germany, and England, and by the end of the 16^th century, paper was being made throughout Europe.

Paper, whether produced in the modern factory or by the most careful, delicate hand methods, is made up of connected fibers. The fibers can come from a number of sources including cloth rags, cellulose fibers from plants, and, most notably, trees. The use of cloth in the process has always produced high quality paper. Today, a large proportion of cotton and linen fibers in the mix create many excellent papers for special uses, from wedding invitation paper stock to special paper for pen and ink drawings.

The methods of making paper is essentially a simple one – mix up vegetable fibers, and cook them in hot water until the fibers are soft but not dissolved. The hot water also contains a base of chemical such as lye, which softens the fibers as they are cooking. Then pass a screen-like material through the mixture, let the water drip off and/or evaporate, and then squeeze or blot out additional water. A layer of paper is left behind. Essential to the process are the fibers, which are never totally destroyed, and, when mixed and softened, from and interlaced pattern within the paper itself. Modern papermaking methods, although significantly more complicated than the older ways, are developmental improvements rather than entirely new methods of making paper.

Probably half of the fibers used for paper today come from wood that has been purposely harvested. The remaining material comes from wood fiber from sawmills, recycled newspaper, some vegetable matter, and recycled cloth. Coniferous trees, such as spruce and fir, used to be preferred for papermaking because the cellulose trees are called “softwood” by the paper industry. Deciduous trees (leafy trees such as poplar and elm) are called “hardwood.” Because of increasing demand for paper, and improvements in pulp processing technology, almost any species of three can now be harvested for paper.

Some plants other than trees are suitable for paper making. In areas without significant forests, bamboo has been used for paper pulp, as has straw and sugarcane.

Most paper is makde by a mechanical or chemical process. Flax, hem, and jute fibers are commonly used for textiles and rope making, but they can also be used for paper. Some high-grade cigarette paper is made from flax.

Cotton and linen rags are used in fine-grade papers such as letterhead and resume paper, and for bank notes and security certificates, the rags are usually cutting and waste from textile and garment mills. The rags must be cut and cleaned, boiled, and beaten before they can be used by the paper mill.

Other materials used in paper manufacture include bleaches and dyes, fillers such as chalk, clay, or titanium oxide, and sizings such as rosin, gum, and starch.

Ahmed Matiur Rahman
Many early civilizations believed that precious possessions, including gems, had strange and mysterious powers and that certain gems could even prevent or cure diseases.These ideas about gems are still preserved in the custom of wearing a birthstone for the month in which one was born. Even though the idea is a very ancient one, the actual wearing of birthstones started about the sixteenth century.Here are the traditional birthstones: January, garnet; February, amethyst; March, bloodstone or aquamarine; April, diamond; May, emerald; June, pearl: July, ruby; August, peridot; September, sapphire; October, opal; November, topaz; December, turquoise.One of the most curious human beliefs is this faith in the power of precious stones. For example, some gems are supposed to have an influence on love and marriage. Tarquoise is believed to prevent disagreement between a husband and wife. Aquamarine promotes the love of married couples. Topaz is a symbol of loyalty. Those who were it are said to be devoted to their husbands or wives for life. Among the stones believed to have the power to cure or prevent illness, the amethyst is considered especially effective against headache and toothache, and diamonds are believed to cure leprosy, insanity and nightmares. Agate reduces fever.Sapphire, it was thought, gave protection from spirits of darkness. The Chinese put jade bracelets or anklets on their children to protect them from harm. The Hindus believe pearls guard them against all evils. The garnet, because it is the color of blood, is worn to make its wearer immune to injury. A turquoise is said to be a charm against falling from a horse. And there are people who believe an opal necklace guards the life and color of blond hair.

]]> http://www.youthwavebd.com/what-is-the-art-of-ceramics/feed/ 0 http://www.youthwavebd.com/where-do-emeralds-come-from/ http://www.youthwavebd.com/where-do-emeralds-come-from/#comments Mon, 01 Nov 2010 06:01:55 +0000 Youth Wave http://www.youthwavebd.com/?p=987 Ahmed Matiur Rahman

In ancient times, the various gems were distinguished only by their colors. The name ruby was given to all precious stones of a red hue. All green stones were called emeralds. All those of blue were called sapphires.
Later on it was seen that some of the gems were harder than others and endured longer. So it came about that the value of a gem depended not only on its color, brilliancy, and rarity, but also on its hardness.
All the gems are called precious stones. But strictly speaking, “precious” is used only for the four most valuable and the sapphire. The other valuable stones are called semi precious.
The emerald is one of the softest of the precious gems. It is a variety of beryl. In this perfect state an emerald is a rich, clear green. But flawless stones are seldom found and for that reason are very expensive.
In ancient times, all the emeralds came from the mines of Egypt. These mines are still marked today but yield only a small quantity of the precious stones. The finest emeralds are at present obtained from the mines near Bogota, Colombia. There are also emerald deposits in the Ural Mountains of Russia and in the Salzburg Alps. A few fine emeralds have been found in North Carolina. And more recent discoveries of emeralds have been made in the Transvaal in South Africa.
There are many legends about emeralds. One of them is that the Holy Grail – the cup from which Christ drank at the Last supper – was carved from a huge emerald. The emerald was believed to have medical power too. It was supposed to have the power of curing the “falling sickness” or epilepsy. Another old legend about the emerald was that it endowed its owner with the gift of foretelling the future. It was said that by looking into its green depths one could see the things that were to come to pass.
The largest known uncut emerald is two inches long and two inches in diameter.

If you’ve ever walked along a beach, you’ve probably seen sea-shells lying on the sand where it has been washed in by the waves. The shell will nearly always be empty, for it is the home of some sea animal that had died.
By the way, shells are also found in wood lands, rivers and ponds as well as the sea. When people speak of shells, they usually mean those of soft bodied animals known as mollusks.

Most mollusks have shells outside their soft bodies. The shell is a mollusk’s skeleton. It is part of the animal and the mollusk is attached to it by muscles. The soft animal inside can never leave its shell and return to it.
The shell is made of a form of limestone and is built by the mollusk itself. Certain glands in the mollusk are able to take lime stone from the water and deposit it in tiny particles at the edge of, and along the inside of, the shell. As a mollusk grows in size, its shell increases in thickness and size. You can see lines of growth that are marked by ridges that sun parallel to the outer edge. You’ve probably noticed these growth lines in the shells of oysters. The other ridges are caused by ridges in the “mantle” of mollusk, or by muscles in its body.
The shell of a mollusk consists of three layers. The outside is covered with a thin layer of hornlike material that contains no line. Under this is a layer of carbonate of lime. The inside layer is the “mother of pearl”, or nacre. It is made up very think alternate layers of carbonate of lime and a horny substance.
The coloring of the shell comes from some glands of the mollusk that contain coloring matter. So a shell may be spotted, all one color, or marked with lines. Some shells are so tiny they can only be seen with a magnifying glass, while the giant clam has a shell that can be four feet long.

We think of frozen food as a new invention, but it is actually one of the oldest methods known for preserving food. From the days when man first inhabited cold regions, he froze fish, game and other meats for future use.
The first known patent for freezing food was granted as early as 18532 in England. The method used was to immerse the food in ice-and-salt brine. Many other patents were granted for freezing food at that time, all using ice-and-salt mixtures.

But frozen foods could not be used extensively until the development of mechanical refrigeration. This made it possible to freeze and transport meats over long distances.

Early in the twentieth century, attempts were made to preserve foods other than meats and fish by freezing. A man called H.S. Baker froze fruits in Colorado as early as 1908. The purpose of this was to freeze the part of the fruit crop that couldn’t be marketed and sell it for use later.

Only certain fruits were frozen at first, chiefly strawberries and cherries. They were frozen by what is known as the cold-pack method. This means placing barrels or containers of the fruit in large storage room where the temperature is maintained at 10 and 15 degrees below zero Fahrenheit.

In 1916, experiments in Germany showed that foods could be frozen by the quick freeze method, which meant freezing the food in a few hours instead of in several days. In 1917 a man called Clavence Birdsage began to work on methods for freezing food in small containers for sale in stores. It wasn’t until 1919 that the first commercial pact of this type was put on the market.

As the result of his experiments and the work of others, it was found that many vegetables could also be preserved in this manner, and the frozen industry was on its way.

Considering what we know about women, it probably won’t surprise you to learn that women have dressed and decorated their hair from as far back as we have any records in history!Combs of some sort or other, for example, have been used by women since the very earliest times. Primitive peoples have made combs of bone, wood, or even bronze.
Primitive people have always paid a great deal of attention to their hair. Some of them have dyed their hair black, white or red. In the Belgian Congo in Africa, natives used the oil from the castor bean for dressing their hair, and many tribes would plaster their hair with mud.
In ancient Greek times, women used long hairpins that were quite elaborate and sometimes had sculpture on them. On special occassions they would adorn their hair with garlands and wreaths of flowers, and they also used ribbons for their hair.
As for what women did about arranging their hair in ancient times, it married from place to place and customs were constantly changing. But even in ancient times, it seems that curled hair was considered more attractive than straigt hair. There are pictures and statues that show women rows of small curls arranged over the brows and temples, and these curls must have been made and kept in place by some artificial means. And not only did men also curl their hair, they even used to curl their breads!
As civilization advanced, hair styles and methods of arranging and dressing the hair became more varied. In some places the style was straight; in others the fashion was curled hair.
The custom of short hair for men and long hair for women is quiet recent in the history of mankind and goes back only to the end of the Middle Ages.