The calculation you’re using is essentially a 2D cross product (or the out‑of‑plane component of a 3D cross product) that’s being applied in a torque context. In physics, torque (τ) is defined as the cross product of the moment arm (r) and the applied force (F):
\tau = \mathbf{r} \times \mathbf{F}.
For planar problems (here using x and z as the axes), the scalar torque is usually given by:
\tau_y = r_x F_z - r_z F_x.
Your expression,