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三角形法则是矢量运算中平行四边形定则的简化.如图1,用平行四边形定则求 F_1和 F_2的合力,则以 F_1和 F_2为邻边作平行四边形 OABC,对角线 OB即是合力∑F.我们会发现 AB 平行且相等于 OC(F_2),也就是说当我们把 F_2按原来方向平移与 F_1首尾相接后,作由 F_1的箭尾到 F_2的箭头的有向线段(如图2)就是图1中的对角线 OB 表示 F_1和F_2的合力∑F,这就是力的三角形法则.根据矢量三角形法则可以得出:物体受同一平面内三个互不平行的力作用处于平衡状态时,这三个力的矢量箭头首尾相接,构成一个矢量三角形.三角形三边的长度对应三个力的大小,夹角确定各力的方向;反之,若三个力的矢量
Triangle rule is the simplification of parallelogram in vector operation, as shown in Figure 1, the parallelogram is used to find the resultant force of F_1 and F_2, then the parallelogram OABC is taken as the adjacent edge of F_1 and F_2, the diagonal OB is the resultant force Σ F. We will find that AB is parallel to OC (F_2), that is to say, when we translate F_2 in the original direction and then connects F_1 with the tail, the directional line of the arrow from F_1 to F_2 2) is the diagonal OB in Figure 1, which shows the resultant force ΣF of F_1 and F_2, which is the triangular law of force. According to the vector triangle law, it can be concluded that the object is balanced by three mutually non-parallel forces in the same plane State, the three force vector arrow end to end, forming a vector triangle.The length of three sides of the triangle corresponds to the size of the three forces, the angle to determine the direction of the force; the other hand, if the three vectors of force