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Flatbow
A flatbow is a bow with non-recurved, flat, relatively wide limbs that are approximately rectangular in cross-section. Because the limbs are relatively wide, flatbows will usually narrow and become deeper at the handle, with a rounded, non-bending handle for easier grip. This design differs from that of a longbow, which has rounded limbs that are circular or D shaped in cross-section, and is usually widest at the handle. A flatbow can be just as long as a longbow, but can be very short. (typical lengths would be say, 68-70" flatbow. 70-72" English longbow. 72-76" warbow weight English longbow, but these styles may easily overlap each other). Traditional flatbows are usually wooden self bows (bows made of one solid piece of wood), though laminated and composite flatbows have been made in ancient and modern times. Modern flatbows commonly use fiberglass.
==Advantages of a rectangular cross-section==
The flatbow is a superior bow design for almost all materials because the stress is more evenly spread out than with rounded limb sections. A bow limb is essentially a flexed beam undergoing bending, and in any flexed beam the farther from the neutral axis (line in the middle of the flexing beam which is not under tension or compression: see diagram in Bending article) the more stress there is within the material. When a limb is rounded, as in a longbow, some material sticks out farther from the neutral axis, and thus is put under greater stress. In a flatbow, the flat belly and back ensure that all of the most strained material is a uniform distance from the neutral axis, spreading the load over a wider limb, minimizing stress and making weaker woods far less likely to fail (break or become permanently bent and lose the resilience needed in a bow). Only particularly resilient timbers can make an effective and powerful wooden longbow.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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