摩擦无处不在,人类依赖摩擦得以生存。即使在最简单的生产活动和日常生活中,人们都懂得用最原始的方法来增加摩擦。例如,向手心吐些口水,可以得心应手地握紧锄头、镰刀等工具,从而提高劳动工效。一些人翻书或清点钞票时,常将手指伸入口中沾些唾液以增加手指与纸面间的摩擦力。 Rubbing is everywhere, and human beings rely on friction to survive. Even in the simplest production activities and daily life, people know how to use the most primitive method to increase the friction. For example, spit some saliva on the palm of your hand, you can easily grip the hoe, sickle and other tools, thereby enhancing labor efficiency. When some people open a book or count their money, they often put their fingers in the mouth to get some saliva to increase the friction between the fingers and the paper.