杠杆,按照它的支点、力点和重点三者之间的相互位置不同,一般可以分成三类。第一类杠杆,它的支点在力点和重点之间。例如日常使用的剪刀,用釘锤拔釘子,称重量的杆秤,都是属于这一类。由于这一类杠杆的支点在力点和重点之间,它又可能有三种情况: (1)支点靠近重点。力点到支点的距离,大于重点到支点的距离,这时使用杠杆就能省力。例如白铁匠用来剪铁皮的剪刀、柄很长,刃口比较短,所以不费很大劲就能剪开铁皮。再如用釘锤拔钉子的时候,釘锤的柄总比较长,因此也能省力,而且我们知道,手执的一点愈是靠近柄的末端,也就是力点到支点的距离愈大,就愈能省力。 (2)支点靠近力点。力点到支点的距离小于重点到支点的距离,这时使用杠杆非但不省力,还会费力。例如裁缝所用的剪刀,柄短而刃口比较长,就是属于这 Leverage, according to its fulcrum, force and focus of the three different positions between each other, can generally be divided into three categories. The first type of leverage, its fulcrum between the force point and the focus. For example, the daily use of scissors, nails nail hammer, weighed weight scale, belong to this category. As the leverage of this type of lever between the force and the focus, it may have three situations: (1) Fulcrum close to the focus. Force point to fulcrum distance, greater than the focus to the fulcrum distance, then use the lever to save energy. For example, the blacksmith used to cut metal scissors, handle long, relatively short cutting edge, so it does not cost a lot of effort to cut the metal. Another example is the nail pulling the nail when the nail hammer hammer handle is always longer, so it can be labor-saving, and we know that the hand is a little closer to the end of the handle, that is, the greater the force point to the fulcrum, the more Can save energy. (2) fulcrum near the force point. The distance between the point of force and the fulcrum is less than the distance between the point and the fulcrum. At this moment, the use of the lever not only saves energy but also saves effort. For example, the scissors used by the tailor, the handle is short and the cutting edge is longer, that belongs to this