Wednesday, December 31, 2008

transport & communication

A mode of transport is a technological solution that used a fundamentally different vehicle, infrastructure and operations. The transport of a person or cargo may be by one or more modes, the latter called intermodal transport. Each mode has its advantages and disadvantages, and will be chosen for a trip depended on the nature of the purpose, cargo and destination. While there transport in air and on water has their own mode, land transport has several modes.
Air
A fixed-wing aircraft, commonly called airplane, is a heavier-than-air craft where movement of the wings in relation to the aircraft is not used to generate lift. The term is used to distinguish from rotary-wing aircraft, where the movement of the lift surfaces relative to the aircraft generates lift. A heliplane is both fixed-wing and rotary-wing. Fixed-wing aircraft range from small trainers and recreational aircraft to large airliners and military
cargo aircraft.
Two necessities for aircraft are air flow over the wings for lift, and an area for landing. The majority of aircraft also need an airport with the infrastructure to receive maintenance, restocking, refueling and for the loading and unloading of crew, cargo and passengers. While the vast majority of aircraft land and take off on land, some are capable of take off and landing on ice, snow and calm water.
The aircraft is the second fastest method of transport, after the rocket. Commercial jets can reach up to 875 kilometres per hour (544 mph), single-engine aircraft 175 kilometres per hour (109 mph). Aviation is able to quickly transport people and limited amounts of cargo over longer distances, but incur high costs and energy use; for short distances or in inaccessible places helicopters can be used.

Rail
Rail transport is the transport of passengers and goods along railways (or railroads), consisting of two parallel steel rails, generally anchored perpendicular to beams (termed sleepers or ties) of timber, concrete or steel to maintain a consistent distance apart, or gauge. The rails and perpendicular beams are usually then placed on a foundation made of concrete or compressed earth and gravel in a bed of ballast to prevent the track from buckling (bending out of its original configuration) as the ground settles over time beneath and under the weight of the vehicles passing above. The vehicles traveling on the rails are arranged in a train; a series of individual powered or unpowered vehicles linked together, displaying markers. These vehicles (referred to, in general, as cars, carriages or wagons) move with much less friction than on rubber tires on a paved road, making them more energy efficient.
A train consists of rail vehicles that move along guides to transport
freight or passengers from one place to another. The guideway
(permanent way) usually consists of conventional rail tracks, but
might also be monorail or maglev. Propulsion for the train is provided
by a separate locomotive, or from individual motors in self-propelled multiple units. Most trains are powered by diesel engines or by electricity supplied by trackside systems, but other sources of power such as steam engine, horses, wire, gravity, pneumatics, or gas turbines are possible.
Rail transport remains the most energy efficient land transport, and used for long-distance freight and all distances of passenger transport. In cities rapid transit and trams are common parts of public transport.

Road
Roads are typically smoothed, paved, or otherwise prepared to
allow easy travel;[2] though they need not be, and historically
many roads were simply recognizable routes without any formal construction or maintenance.[3] In urban areas roads may pass through a city or village and be named as streets, serving a dual function as urban space easement and route.[4]
The most common road vehicle is the automobile; a wheeled passenger vehicle that carries its own motor. Other users of roads include buses, trucks, motorcycles, bicycles and pedestrians. As of 2002 there were 590 million automobiles worldwide.
The first forms of road transport were horses, oxen or even humans carrying goods over dirt tracks that often followed game trails. The Roman Empire was in need for armies to be able to travel quickly; they built deep roadbeds of crushed stone as an underlying layer to ensure that they kept dry, as the water would flow out from the crushed stone, instead of becoming mud in clay soils. John Loudon McAdam designed the first modern highways of inexpensive paving material of soil and stone aggregate known as macadam during the Industrial Revolution. Coating of cobblestones and wooden paving were popular during the 19th century while tarmac and concrete paving became popular during the 20th.
Automobiles offer high flexibility and with low capacity, but are deemed with high energy and area use, and the main source of noise and air pollution in cities; buses allow for more efficient travel at the cost of reduced flexibility. Road transport by truck is often the initial and final stage of freight transport.

Water
Ship transport is the process of transport by barge, boat, ship or
sailboat over a sea, ocean, lake, canal or river. A watercraft is a
vehicle designed to float on and move across (or under) water.
The need for buoyancy unites watercraft, and makes the
hull a dominant aspect of its construction, maintenance and appearance.
The first craft were probably types of canoes cut out from tree trunks. The colonization of Australia by Indigenous Australians provides indirect but conclusive evidence for the latest date for the invention of ocean-going craft. Early sea transport was accomplished with ships that were either rowed or used the wind for propulsion, or a combination of the two.
In the 1800s the first steam ships were developed, using a steam engine to drive a paddle wheel or propeller to move the ship. The steam was produced using wood or coal. Now most ships have an engine using a slightly refined type of petroleum called bunker fuel. Some specialized ships, such as submarines, use nuclear power to produce the steam. Recreational or educational craft still use wind power, while some smaller craft use internal combustion engines to drive one or more propellers, or in the case of jet boats, an inboard water jet. In shallow draft areas hovercraft are propelled by large pusher-prop fans.
Although slow, modern sea transport is a highly effective method of transporting large quantities of non-perishable goods. Transport by water is significantly less costly than air transport for trans-continental shipping;[5] short sea shipping and ferries remain viable in coastal areas.

No comments:

Post a Comment