A windmill is a machine which translates linear motion of wind to rotational motion by means of adjustable vanes called sails. The main use is for a grinding mill powered by the wind, reducing a solid or coarse substance into pulp or minute grains by crushing, grinding, or pressing. Other uses of windmill are Wind energy conversion systems as windpumps and wind turbines. The first practical windmills were the vertical axle windmills invented in eastern Persia, as recorded by the Persian geographer Estakhri in the 9th century. The authenticity of an earlier anecdote of a windmill involving the second caliph Umar is questioned on the grounds that it appears in a 10th-century document.

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