自行车(bicycle)，亦称脚踏车。由骑车者驱动的轻型、两轮、可操控的机械。两个轮子安装在金属框架上，前轮固定於可转动的前叉上。骑车者坐在座垫上，由连接前叉的把手来操控，踩动一个连接两个曲柄的链轮，曲柄上装有脚踩的踏板。动力经由绕在两个链轮上的环形链条从这个链轮传至後轮上的第二个链轮。1818年出现一种笨重、无踏板的两轮车，骑车者仅能以双足蹬地前进。1839年苏格兰铁匠麦克米伦（Kirkpatrick Macmillan, 1813～1878）制作出一种自行车，有踏板、曲柄和驱动连杆，被公认是自行车的发明者。1861年法国的皮耶.米肖（Pierre Michaux）和恩斯特.米肖（Ernest Michaux）引进了重要的革新发明，到1865年他们一年可生产四百辆这种实用的脚踏车。1870年英格兰生产出前轮大後轮小的更轻型的自行车。1890年代已建立标准的自行车设计模式，并用了新型充气轮胎增加其平稳性，从而使自行车很快流行起来。到了20世纪，自行车不断改进，如采用更轻的框架和改良的齿轮和刹车。自行车已在全世界广泛使用，在许多国家成为基本的交通工具。

English version：

bicycle

Lightweight, two-wheeled, steerable machine that is propelled by the rider. The wheels are mounted in a metal frame, and the front wheel is held in a movable fork. The rider sits on a saddle and steers by handlebars attached to the fork, propelling the bicycle by two pedals attached to cranks that turn a driving sprocket. An endless chain transmits power from the driving sprocket to a back-wheel sprocket. A heavy pedalless form built in 1818 was propelled simply by the rider paddling his feet against the ground. In 1839 the Scottish blacksmith Kirkpatrick Macmillan (1813-1878) built a bicycle propelled by pedals, cranks, and drive rods; he is widely credited with inventing the bicycle. Important innovations were introduced by Pierre and Ernest Michaux in France in 1861, and by 1865 their company was manufacturing 400 vélocipèdes a year. A lighter version produced in England in 1870 (nicknamed the “penny-farthing”) featured a large front wheel and small back wheel. By the 1890s the standard bicycle design was established, and with the smooth ride enabled by the new pneumatic tires its popularity exploded. 20th-century improvements included lighter frames and improved gears and brakes. Widely used throughout the world, it is a basic means of transportation in many countries. See also bicycle industry.

参考文章

• 助动自行车第三者责任保险的保险责任：保险
• 新型电动自行车开启生活新时尚生态安全
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• 冰雪路上骑自行车怎样注意安全居家/装修
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• 值得倡的骑自行车健身保健养生
• 为什么患有腰椎间盘突出症的病人走路困难，但却能骑自行车？骨科
• 怎样防止自行车被盗居家/装修