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.
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立春那天去超市买春饼，空气里刺骨的寒气似乎一点也没有春意。不承想，隔两日再次出门，照例把脖子往衣领里缩，却隐约发现整个冬天伴着哨音蛮横且有刺痛感的气流正在消退，虽寒意尚在，风却变弱了、变软了，感觉脸上装备的那层抵御寒冬的铠甲，迅速融作一袭若有若无的轻纱。微风徐来，习惯中那种粗粝的刮痛感不见了，取而代之的是一种在清泉里漂洗了许久的凉润润的、绸缎般的温润触感。这变化极其轻微，似乎正缓慢地从时间的罅隙、从空间最微末的颤动中溢出，仿佛宇宙经过漫长的沉睡，打着困意尚未全消的呵欠渐渐苏醒，意在向世间表明，季节的轮替正一如既往地、温和而守时地、捧着新生的希望如期而至。
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