separate matrix equation

Question

I want to separate my matric because its over the column size like patter below.

from 
Vm(q,qdot) = [matrix]
 to
Vm(q,qdot)
and not 


\begin{equation}
\label{eq6}
\begin{array}{c}
V_m (\bf {q}, \bf{\dot {q}})
\end{array} \\
 = 
\newline \left[
\begin{array}{cccccc}
m_1 & 0 & 0 & 0 & 0 & 0 \\
0 &  m_2 & 0 & 0 & 0 & 0 \\
0 &  0 & m_3 & 0 & 0 & 0 \\
0 &  0 & 0 & 0 & I_z{\dot{\psi}}  & -I_y{\dot{\theta}} \\
0 &  0 & 0 & -I_z{\dot{\psi}}  & 0 & J_t{\omega}+I_x\dot{\phi}   \\
0 &  0 & 0 & I_y{\dot{\theta}} & -J_t{\omega}-I_x\dot{\phi}   & 0    \nonumber
 \end{array}
\right]
\end{equation}

Answer 1

You're using quite old syntax (\bf in math mode, for example).

I suggest you to load the amsmath package, that gives many useful new environments for writing math efficiently.

A \newline is not allowed in a math display such as equation. With amsmath there is multline with its unnumbered variant multline*:

\begin{multline*}
V_{m}(\mathbf{q}, \dot{\mathbf{q}})=\\ % break here
\begin{bmatrix}
m_1 & 0 & 0 & 0 & 0 & 0 \\
0 & m_2 & 0 & 0 & 0 & 0 \\
0 & 0 & m_3 & 0 & 0 & 0 \\
0 & 0 & 0 & 0 & I_z\dot{\psi}  & -I_y\dot{\theta} \\
0 & 0 & 0 & -I_z\dot{\psi}  & 0 & J_t\omega+I_x\dot{\phi}   \\
0 & 0 & 0 & I_y\dot{\theta} & -J_t\omega-I_x\dot{\phi}   & 0
\end{bmatrix}
\end{multline*}