先解釋 Moment 是甚麼吧 用 scalar 的說法是這樣 Let X be the axis to be considered Moment about X due to a force F =smallest distance between X and the line of action * F (line of action 就是把 vector F 無限延長那條線) 明白嗎?不明白也沒關係,因為將會把問題簡化 moment 跟 torque 其實是一樣的 所以 quote wiki, Torque is the tendency of a force to rotate an object about an axis
然後是正題 "The sum of torques due to several forces applied to a single point is equal to the torque due to the resultant force" 這裡的 sum 都是 vector sum,所以如果是3D,用 scalar 解釋會很複雜
簡化問題 由3D變成2D Consider A as a point on the plane Then take X as the line passing through A perpendicular to the plane
Moment about point A =distance between A and the line of action * F 而不難想像 rotation 的方向是順/逆時針 Denote 其中一個方向是正,另一個為負 之後 sum of torques 就用可以直接加
