Need to raise/lower equation number using tex macros given point value as variable.
\documentclass{book}
\usepackage{amsmath}
\begin{document}
If the car in figure has a linear acceleration parallel to the ground, a point on the tyre's outer edge experiences a tangential acceleration relative to the axle. The same kind of reasoning as that used in the previous paragraph reveals that the magnitudes of these accelerations are the same and that they are related to the angular acceleration of the wheel relative to the axle.
\begin{align}%%\raisetag{30pt}
\begin{array}{ll}
\underset{\text{Linear speed}}{\underbrace{v}}=\underset{\text{Tangential speed}}{\underbrace{v_{\mathrm{T}}=r\omega }} & \left(\omega \text{~in~}\mathrm{rad}/\mathrm{s}\right)\end{array}%
\tag{8.12}%%\eqnoraise{30pt}{\tag{8.12}}
\end{align}
If the car in figure has a linear acceleration parallel to the ground, a point on the tyre's outer edge experiences a tangential acceleration relative to the axle. The same kind of reasoning as that used in the previous paragraph reveals that the magnitudes of these accelerations are the same and that they are related to the angular acceleration of the wheel relative to the axle.
\end{document}