Q.A force of $25\ \text{N}$ is applied at the end of a wrench of length $0.3\ \text{m}$ to turn a bolt.

Torque (or moment of a force) is the rotational analogue of force, defined as $\vec{\tau}=\vec{r}\times\vec{F}$, where $\vec{F}$ is the applied force and $\vec{r}$ is the position vector of its point of application measured from the axis of rotation; its magnitude is $\tau=rF\sin\theta$, where theta is the angle between $\vec{r}$ and $\vec{F}$. A force's rotational effectiveness depends on three things: the force's magnitude, how far from the axis it is applied (larger r gives larger torque), and the angle at which it is applied (maximum effect at 90 degrees, zero effect when applied along the line to the axis).

Because torque involves a definite sense of rotation (clockwise or anticlockwise), it is a vector quantity, with direction given by the right-hand rule -- conventionally drawn using a dot for a vector pointing out of the page and a cross for one pointing into the page. Torque depends not only on the magnitude and direction of a force but critically on the axis of rotation chosen and the exact point where the force is applied relative to that axis -- unlike the torque of a couple (below), which is independent of the axis.