I know that stiffness,$K$ is equal to product of moment of inertia and square of the natural frequency
$$ K=J\omega_n{}^2$$
Where $K$ = stiffness, $J$ = moment of inertia and $\omega_n$ = natural frequency.
SI unit of $J$ is $\textrm{kg m}^2$, while SI unit of $\omega_n$ is radians per second, but as shown in attached snap, SI unit of K is $\textrm{Nm}/\textrm{radian}$. I have tried to solve and simplify the product of units of $J$ and $\omega_n$, but I am unable to understand how we get unit of K as $\textrm{Nm}/\textrm{radian}$ because i get units as $\textrm{Nm radian}^2$
