🎬Why the difference vector is orthogonal at the points of closest approach

The visualization is designed to dynamically demonstrate the geometric principle of finding the shortest distance between two skew lines in 3D space. The animation achieves this by synchronously oscillating the parameters $t$ and $s$ around their calculated optimal values ( $t_{\text {opt }}$ and $s_{\text {opt }}$ ), which causes the points $X_1$ and $X_2$ to sweep along their respective lines. The key takeaway is the direct causal link between the minimum distance and vector orthogonality: the difference vector $d$ connecting $X_1$ and $X_2$ achieves its shortest length only at the single instant when it becomes perpendicular to both line direction vectors, $v_1$ and $v_2$ . This critical state is confirmed mathematically by the dynamic display showing both dot products ( $\left|d \cdot v_1\right|$ and $\left|d \cdot v_2\right|$ ) simultaneously approaching zero, and visually by the $d$ vector changing color, illustrating that minimum distance necessitates orthogonality.