If $\overrightarrow F $ is the force acting on a particle having position vector $\overrightarrow r $ and $\overrightarrow \tau $ be the torque of this force about the origin, then
$\overrightarrow r .\overrightarrow \tau > 0$ and $\overrightarrow F .\overrightarrow \tau < 0$
$\overrightarrow r .\overrightarrow \tau = 0$ and $\overrightarrow F .\overrightarrow \tau = 0$
$\overrightarrow r .\overrightarrow \tau = 0$ and $\overrightarrow F .\overrightarrow \tau \ne 0$
$\vec r.\vec \tau \ne 0$ and $\overrightarrow F .\overrightarrow \tau = 0$
