我们知道,当物体存在向上的加速度时,它对支持物的压力(或对悬挂物的拉力)大于它的重量,即N(T)=mg+ma,叫超重现象;当物体存在向下的加速度时,它对支持物的压力(或对悬挂物的拉力)小于它的重量,即N(T)=mg-ma,叫失重现象。这两个公式是利用牛顿第二定律和牛顿第三定律结合起来分析物体超重和失重时得出的。对有些常见习题直接运用超重和失重现象进行分析、并利用公式计算,要比利用牛顿第二定律和牛顿第三定律结合起来分析求解,既方便又不容易出现错误。但首先必须弄清公式中的质量和加速度的含义。即m应是超垂或失重物体(或物体系)的质 We know that when there is an upward acceleration of an object, its pressure on the support (or the tension on the suspended object) is greater than its weight, that is, N(T) = mg + ma, called overweight phenomenon; when the object exists downward Acceleration, its pressure on the support (or pull on the suspension) is less than its weight, that is, N (T) = mg-ma, called the phenomenon of weight loss. These two formulas are derived from the combination of Newton’s second law and Newton’s third law when analyzing objects for overweight and weightlessness. It is more convenient and not prone to errors than to use the Newton’s second law and Newton’s third law to combine the analysis and solution to the direct use of overweight and weightlessness in some common exercises and to use formulas. But first we must understand the meaning of the mass and acceleration in the formula. That is, m should be the mass of a super-sag or weightless object (or system)