Yumi
The was an important weapon of the samurai warrior during the feudal period of Japan. It is typically shot with Japanese arrows known as . History. Early Japanese (pre-3rd century CE) used bows of various sizes, but the majority were short with a centre grip. This style of bow was called the and was constructed using a small sapling or tree limb. It is unknown when the asymmetrical came into use, but the first written record is found in the "Book of Wei", a Chinese historical manuscript dating to the 3rd century CE, which describes the people of the Japanese  islands using "spears, shields, and wooden bows for arms; the wooden bows are made with the lower limbs short and the upper limbs long; and bamboo arrows with points of either iron or bone." The oldest asymmetrical found to date was discovered in Nara Prefecture, and is estimated to be from the 5th century. During the Heian period (794–1185) the length of the was fixed at a little over , and the use of laminated construction was adopted from the Chinese. By the end of the 10th century, the Japanese had developed a two piece bamboo and wood laminated . Over the  next several hundred years the bow's construction evolved, and by the 16th century the design was considered to be nearly perfect. The modern bamboo is practically identical to the of the 16th and 17th centuries. Shape. The is exceptionally tall, standing over , and typically surpasses the height of the . They are traditionally made by laminating bamboo, wood and leather, using techniques which have not changed for centuries, although some archers (particularly beginners) may use a synthetic . The is asymmetrical; according to the All Nippon Kyudo Federation, the grip () has to be positioned at about two thirds of the distance  from the upper tip. The upper and lower curves also differ. Several hypotheses have been offered for this asymmetric shape. Some believe it was designed for use on a horse, where the could be moved from one side of the horse to the other with ease; however, there is evidence that the asymmetrical shape predates its use on horseback. Others claim that asymmetry was needed to enable shooting from a kneeling position. Yet another explanation is the characteristics of the wood from a time before laminating techniques. In case the bow is made from a single piece of wood, its  modulus of elasticity is different between the part taken from the treetop side and the other side. A lower grip balances it. The hand holding the may also experience less vibration due to the grip being on a vibration node of the bow. A perfectly uniform pole has nodes at 1/4 and 3/4 of the way from the ends, or 1/2 if held taut at the ends – these positions will change significantly with shape and consistency of the bow material. String. The string of a , a , is traditionally made of hemp, although most modern archers will use strings made of  synthetic materials such as Kevlar, which will last longer. Strings are usually not replaced until they break; this results in the flexing in the direction opposite to the way it is drawn, and is considered beneficial to the health of the . The nocking-point on the string is built up through the application of hemp and glue to protect the string and to provide a thickness which helps hold the nock ( of the arrow, a , in place while drawing the . However, it can also be made of strands of waxed bamboo. Care and maintenance. A bamboo requires careful attention. Left  unattended, the can warp out of shape and may eventually become unusable. The shape of a will change through normal use and can be re-formed when needed through manual application of pressure, through shaping blocks, or by leaving it strung or unstrung when not in use. The shape of the curves of a is greatly affected by whether it is left strung or unstrung when not in use. The decision to leave a strung or unstrung depends upon the current shape of the . A that is relatively flat when unstrung will usually be left unstrung when not in use  (a in this state is sometimes referred to as being 'tired'). A that has excessive curvature when unstrung is typically left strung for a period of time to 'tame' the . A well cared-for can last many generations, while the usable life of a mistreated can be very short. history. The bow, from the late Jōmon period which ended about 400 BCE, is laminated.