Physics

The key insight is that torque $\vec{\tau} = \vec{r} \times \vec{F}$ depends on the perpendicular component of force relative to the position vector. When force points parallel (or antiparallel) to $\vec{r}$, the cross product of two collinear vectors is zero—there's no "twisting" effect because the force pulls or pushes straight through the origin rather than around it. This is why central forces, like gravity, produce no torque about the center they point toward.

The key insight is that torque $\vec{\tau} = \vec{r} \times \vec{F}$ depends on the perpendicular component of force relative to the position vector. When force points parallel (or antiparallel) to $\vec{r}$, the cross product of two collinear vectors is zero—there's no "twisting" effect because the force pulls or pushes straight through the origin rather than around it. This is why central forces, like gravity, produce no torque about the center they point toward.