大小相等，方向相反 meaning in English

equal and opposite in direction

The condition of equilibrium of the member requires that the pair of forces coming from the joints must be equal and opposite .
元件的平衡条件要求来自连接点的一对力必须大小相等，方向相反。
To every action there is always opposed an equal reaction ; or , the mutual actions of two bodies upon each other are always equal , and directed to contrary parts
两个物体的相互作用力总是大小相等，方向相反，同时出现或消失且作用于同一直线上。