The fundamental principles（基本原理）involved in （涉及）applying this method are easy to understand and develop（阐述）.
力法最初由James Clerk Maxwell 在1864提出，后由Otto Mohr和Heinrich Muller-Breslau加以提炼。该法是最早可采用的分析超静定结构的方法之一。正如其名称所提示的，力法包括写出满足结构协调要求和力-位移要求的方程以及涉及未知冗余力的方程。这些未知力的系数称为柔度系数。由于协调性形成了这个方法的基础，它有时被称为协调法或位移协调法。通过满足结构的平衡要求来确定冗余力。涉及该法运用的基本原理是很容易理解和阐述的。
When Marxwell developed the force method of analysis, he also published（发表）a theorem that relates（使..互相关联） the flexibility coefficients of any two points on an elastic structure – be it a truss, a beam, or a frame. This theorem is referred to as the theorem of reciprocal displacements（位移互等定理）and may be stated as follows（陈述如下）: The displacement of a point B on a structure due to a unit load acting at point A is equal to the displacement of point A when the unit load is acting at point B, that is fBA = fAB. The theorem also applies for reciprocal rotations（转角互等）. Furthermore, using a unit force and unit couple moment, applied at separate（分开的）points on the structure, we may also state: The rotation in radians（以弧度为单位）at point B on a structure due to a unit load acting at point A is equal to the displacement at point A when a unit couple moment is acting at point B.
当Marxwell提出力法分析时，他也发表了使弹性结构上任意两点的柔度系数相关的定理-无论是桁架、梁或框架。该定理称为位移互等定理，可以陈述如下：由作用在结构上A点的单位力引起B点的位移等于当单位力作用在B点时引起的A点的位移，即fBA = fAB。该定理也适用于转角互等。而且，将单位力和单位力偶矩施加在结构上不同的点，我们也可以陈述为：由作用在结构上A点的单位力引起B点的转角（单位为弧度）等于当单位力偶矩作用在B点时引起的A点的位移。
The displacement / stiffness method of analysis is based on first writing force-displacement relations（关系式）for the members and then satisfying the equilibrium requirements for the structure. In this case the unknowns（未知量）in the equations are displacements and their coefficients are called stiffness coefficients. Once the displacements are obtained, the forces are determined from the compatibility and force-displacement equations.
位移法或刚度法的分析是基于最初写出的构件的力-位移关系式，并且要满足结构的平衡要求。在这种情况下，方程式中的未知量是位移，而它们的系数称为刚度系数。一旦求得位移，就可从协调方程和力-位移方程中确定力。
Early in the 20th century slope deflection（转角位移法）was the most popular（流行的）method in use for analyzing statically indeterminate frames. It was developed by Professor G.A. Maney and began its reign of popularity（开始盛行）almost immediately after its publication（发表）in 1915. Fifteen years later the moment distribution method（弯矩分配法）was introduced and there began a period of spirited professional competition （激烈的专业竞争）over the merits（优势）of the two methods, with moment distribution eventually emerging as the “winner”, primarily because of its speed and simplicity. But the competition has not ended. Today, although moment distribution continues as（依然作为）the more popular method, there remain many contemporary（同时代的）engineers who prefer slope deflection.
早在20世纪，转角位移法是用以分析超静定框架最流行的方法。它由G.A. Maney教授提出，并在1915年发表后几乎迅速开始盛行。15年后弯矩分配法被采用，并在一段时期内开始了对两种方法的优势展开的激烈的专业竞争，弯矩分配法最终以胜者出现，主要是由于它的速度和简单。但是竞争没有结束。今天，尽管弯矩分配法依然作为较流行的方法，仍有很多同时代的工程师较喜欢用转角位移法。
They contend（辩解）that in performing a slope deflection analysis the engineer can acquire a better “intuitive feel”（直觉）for the structure than the use of any other method. More significant（重要的）, though, slope deflection has gained renewed（重新）importance（重要地位）with the advent（到来）of the computer, serving as（作为）the central method（重要方法） used for structural analysis software. Slope deflection focuses on（着重于）individual members, their loads, and certain conditions at their ends.
他们辩解在进行转角位移分析时能比在使用任何其它的方法中获得对结构更好的直觉。然而更重要的是，转角位移法由于计算机的到来已经重新获得了重要地位，作为用于结构分析软件的重要方法。转角位移法着重于单个构件、作用于它们的荷载和端部的某些条件。
In using this method, simultaneous equations（联立方程）are written and solved that have displacements, rather than forces or moments, as unknowns. It employs a simple sign convention（符号约定）: all variables（变量）related to a member are positive（正的）if they are clockwise（顺时针的）. The complete slope deflection equations for MAB and MBA are the superpositions of four parts: A, B, , and loads. Thus
MAB = 4EI/L A +2EI/L B -6EI/L2 +FEMAB （5-3） MBA = 2EI/L A +4EI/L B -6EI/L2 +FEMBA （5-4）