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Since not many people - in fact hardly any at all - master the art of flying, man invented the aircraft.
The principle behind all aircraft is that they create an upward force that is equal to the force of gravity acting upon the aircraft and its occupants. There are two basic ways to achieve this:
An aircraft wing (and helicopter rotor blade) is shaped such that the upper surface is curved. This means that as the aircraft wing moves through the air, the air passing over the top surface passes over the wing faster than under the wing. The speed change has an effect on the pressure of the air, and that effect is governed by Bernoulli's Principle. It's quite a complicated law, but basically when air is moving in a streamlined flow (ie smooth and not turbulent), in areas where the airspeed increases, the air pressure decreases; and conversely, where the airspeed decreases, the air pressure increases The resulting pressure difference between the air above and below the wing lifts it up. Also, the wing is usually inclined to the airflow at a slight positive angle so that it deflects some of the airflow downwards. The resulting 'downwash' results in an upward force which adds to the lift, though not as much as the lift generated by the top surface of the wing.
When the weight of the aircraft is less than the weight of the air around it a phenomenon called buoyancy occurs.
Buoyancy was discovered by Archimedes who spent most of his days in bathtubs, and for a very long time people thought it was only applicable to water and ships. The French Montgolfier brothers pioneered this method of flight in June 1783, and a somewhat frightened sheep, a duck and a cockerel were the first passengers on their hot air balloon. Apart from the fact that their contraption actually worked, one of the most astonishing features for spectators at the time must have been the awful stench. The Montgolfier brothers mistakenly believed that foul smelling smoke was the cause of the upward force and therefore burnt whatever produced the foulest smells, including such things as rotting carcasses!
Aircraft come in all shapes and sizes. They can be anything from a collection of tubes and fabric, that can carry their single pilot/passenger about the length of a football field up to high tech triumphs of engineering that can transport several hundred passengers halfway across the globe. Unfortunately for hitch hikers, it is almost impossible to catch a lift on aircraft capable of travelling any worthwhile distance. Do not be fooled by advertised 'hitch hiker fares'. These may be slightly less expensive than other fares, but are by no means cheap, and many basic services such as a seat, a cabin roof and toilet access usually come at a premium.