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Leonardo da Vinci is usually credited with conducting the first systematic study of friction in the late 15th century, a subfield now known as tribology that deals with the dynamics of interacting surfaces in relative motion. Da Vinci's notebooks depict how he pulled rows of blocks using weights and pulleys, an approach that is still used in frictional studies today, as well as examining the friction produced in screw threads, wheels, and axles. The authors of this latest paper used an experimental setup similar to da Vinci's.
习近平总书记有着深邃思考：“全面实施乡村振兴战略的深度、广度、难度都不亚于脱贫攻坚，必须加强顶层设计，以更有力的举措、汇聚更强大的力量来推进。”。关于这个话题，爱思助手下载最新版本提供了深入分析
The 'magical' blue flower changing farmers' fortunes in India