齿轮是一种连动装置,轮边缘是密布的锯齿,两轮齿齿相压, 紧紧相嵌,于是有了“一随一”的机械转动。滑轮,是一种动力装置。只不过轮边光滑无棱,一条皮带就可使其灵活自如地转动。 The gear is a kind of interlocking device. The edge of the wheel is a dense sawtooth. The two teeth are pressed against each other and tightly embedded so that there is a “one by one” mechanical rotation. Pulley, is a power device. Only the edges of the wheels are smooth and ribbed, and a belt allows them to turn freely.