- #1
- 996
- 5
Homework Statement
Using index-comma notation only, show:
\begin{equation*}
\underline{\bf{v}} \times \text{curl } \underline{\bf{v}}= \frac{1}{2} \text{ grad}(\underline{\bf{v}} \cdot \underline{\bf{v}}) - (\text{grad } \underline{\bf{v}}) \underline{\bf{v}}
\end{equation*}
Homework Equations
\begin{align*}
\text{ curl } \underline{\bf{v}} &= \epsilon_{ijk} v_{j,i} \underline{\bf{e}}_k \\
\underline{\bf{v}} \times \underline{\bf{u}} &= \epsilon_{ijk} v_i u_j \underline{\bf{e}}_k
\end{align*}
The Attempt at a Solution
If I let [itex] \underline{\bf{u}} =\text{ curl } \underline{\bf{v}}[/itex] we get:
\begin{align*}
\underline{\bf{u}} &= \text{ curl } \underline{\bf{v}} =\epsilon_{prq} v_{r,p} \underline{\bf{e}}_q \\
u_j &= \epsilon_{prq} v_{r,p} \underline{\bf{e}}_q \cdot \underline{\bf{e}}_j \\
u_j &= \epsilon_{prq} v_{r,p} \delta_{qj} = \epsilon_{prj} v_{r,p} \\
\underline{\bf{v}} \times \underline{\bf{u}} &= \epsilon_{ijk} v_i u_j \underline{\bf{e}}_k \\
&= \epsilon_{ijk} \epsilon_{prj} v_i v_{r,p} \underline{\bf{e}}_k
\end{align*}
Is this correct so far? Trouble is, I'm not sure what to do next. I'm wondering if trying to simplify [itex]\epsilon_{ijk} \epsilon_{prj}[/itex] would be a fruitful approach. Appreciate hints/tips. Thanks!
Last edited: