الوسم: Bicycle

* Introduction :

The bicycle, bike, or cycle is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind the other. Invented in Europe in the 19th century, the bicycle has become the world’s most popular vehicle with about 1.4 billion in use.
In addition to transport, bicycles also provide a popular form of recreation, and have been adapted for use in many other fields of human activity, including children’s toys, adult fitness, military and police applications, courier services, and cycle sports.

* Presentation :

History

Several innovators contributed to the history of the bicycle by developing precursor human- powered vehicles. The $$$$$$$$ed ancestors of today’s modern bicycle were known as push bikes, Draisines or hobby horses. To use the Draisine, first introduced to the public in Paris by the German Baron Karl von Drais in 1818 , the operator sat astride a wooden frame supported by two in-line wheels and pushed the vehicle along with his/her feet while steering the front wheel.

Scottish blacksmith Kirkpatrick MacMillan refined this in 1839 by adding a mechanical crank drive to the rear wheel, thus creating the first true "bicycle" in the modern sense. In the 1850s and 1860s, Frenchmen Pierre Michaux and Pierre Lallement took bicycle design in a different direction, placing the pedals on an enlarged front wheel. Their creation, of wrought iron and wood, developed into the "penny- farthing" (more formally an ordinary bicycle), featuring a tubular steel frame on which were mounted wire spoked wheels with solid rubber tires. These bicycles were not, however, for the faint hearted, due to the very high seat and poor weight distribution.

The subsequent dwarf ordinary addressed some of these faults by reducing the front wheel diameter and setting the seat further back, necessitating the addition of gearing, effected in a variety of ways, to attain sufficient speed. However, having to $$$$ pedal and steer via the front wheel remained a problem. Starley’s nephew, J. K. Starley, J. H. Lawson, and Shergold solved this problem by introducing the chain drive connecting the pedals held with the frame to the back wheel. These models were known as dwarf safeties, or safety bicycles, for their lower seat height and better weight distribution. Starley’s 1885 Rover is usually described as the first recognizably modern bicycle. Soon, the seat tube was added, creating the double-triangle diamond frame of the modern bike.
New innovations increased comfort, and ushered in a second bicycle craze, the 1890s’ Golden Age of Bicycles. In 1888, Scotsman John Boyd Dunlop introduced the pneumatic tire, which soon became universal. Soon after, the rear freewheel was developed, enabling the rider to coast without the pedals spinning out of control. This refinement led to the 1898 invention of coaster brakes. Derailleur gears and hand-operated cable-pull brakes were also developed during these years, but were only slowly adopted by casual riders. By the turn of the century, cycling clubs flourished on $$$$ sides of the Atlantic, and touring and racing were soon extremely popular.
Bicycles and horse buggies were the two mainstays of private transportation just prior to the automobile, and the grading of smooth roads in the late 19th century was stimulated by the wide use of these devices.

Uses for bicycles

Bicycles have been and are employed for many uses.

— Utility: bicycle commuting and utility cycling
— Work: mail delivery, paramedics, police, and general delivery.
— Recreation: bicycle touring, mountain biking, BMX and physical fitness.
— Racing: track racing, criterium, roller racing and time trial to multi-stage events like the Giro d’Italia, the Tour de France, and the Vuelta a España.
— Military: scouting, troop movement, supply of provisions, and patrol. See bicycle infantry.
— Show: entertainment and performance, e.g. circus clowns

Technical aspects

Since the first bicycle, many important details have been improved, especially with the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized bicycle types.

Types of bicycle

Bicycles can be categorized in different ways: e.g. by function, by number of riders, by general construction, by gearing or by means of propulsion. The common types include utility bicycles, mountain bicycles, racing bicycles, touring bicycles, cruiser bicycles, and BMX bicycles. Less common types include tandems, recumbents, lowriders, tall bikes, fixed gear, and folding models. Unicycles, tricycles and quadracycles are not strictly bicycles, as they have respectively one, three and four wheels, but are often referred to informally as "bikes".

Legal requirements

The 1968 Vienna Convention on Road Traffic of the United Nations considers a bicycle to be a vehicle, and a person controlling a bicycle is considered a driver. The traffic codes of many countries reflect these definitions and demand that a bicycle satisfy certain legal requirements, sometimes even including licensing, before it can be used on public roads. In many jurisdictions it is an offence to use a bicycle that is not in roadworthy condition.
In most jurisdictions, bicycles must have functioning front and rear lights when ridden after dark. As some generator or dynamo-driven lamps only operate while moving, rear reflectors are frequently also mandatory. Since a moving bicycle makes little noise, some countries insist that bicycles have a warning bell for use when approaching pedestrians, equestrians and other bicyclists.

* Conclusion :

Bicycles are useful and clean means of transport . They have been and are employed for many uses . They can be categorized in different ways , so we can use them in defferent way .

* Recommendation :