Wheel
Often regarded as the symbol of the
beginning of inventiveness of the human race, the origin of the
wheel is unknown. It has been suggested that it may have derived
from the wheel used in pottery, itself possibly
derived from earlier work in the crafting of the
basket. The earliest evidence of the use of the
wheel in transportation can be traced to about 3500 to 3200 B.C. in
Mesopotamia (modern <?xml:namespace prefix = st1 ns =
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possible that the wheel may have been introduced as early as 4000
B.C., but no direct evidence has been found to demonstrate that.
The physical nature of the wheel and axle combination is such that
its rotary motion can be continuous in direction and magnitude and
that a pulled or pushed object on a wheeled base greatly reduces
friction. With the addition of connecting rods, the wheel found
many applications in later generations beyond transportation in the
construction of machinery. Wheels and axles were the essential
components of the pulley, developed before 1500
B.C. The popular picture of a "caveman" chipping out a stone wheel
derives from a misconception that the wheel dates from Paleolithic
times. In fact, the wheel is a relatively recent invention, of the
late Neolithic period associated with agriculture
and the development of the first cities. Artifacts
and models of two- and four wheeled carts have been dated to about
2600 B.C. The earliest wheels were constructed from three wooden
planks clamped together with copper or wooden fixtures (clamps or
battens) and then carved into a rounded shape. A hole in the center
for an axle was often surrounded by a raised hub for support Such a
construction of the earliest known wheels can be suggested as an
argument that the wheel did not derive from adaptation of roller
logs. However, the transition may have come as craftsmen attempted
to reduce the need to smooth wide sections of ground by narrowing
the center of a log roller, leaving wider diameters at the ends and
clearance in the middle. However, a section of a log, when used as
a wheel, would be far less durable than the braced plank structure
found in the early Sumerian wheels. The first wheels with spokes,
used on chariots, appeared in about 2000 B.C. The fact that the
advanced civilizations of the NewWorld, including the Toltec, the
Maya, and the Inca Empire, did not develop the wheel for
transportation but made use of it for pull toys for children has
represented a major puzzle in the history of the application of
technology. The Mexican toys were made of clay, with miniature clay
rollers. The presence of large numbers of slave laborers has been
adduced as a reason that no practical development for land
transport, even the wheelbarrow, was required, but the ancient
civilizations of Mesopotamia, Sumeria, and Egypt, where wheels were
widely adopted, were also characterized by slave labor
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Community
Wheel
