Axial strain rate
= Axial strain rate
{title2=$E=\partial w/\partial z$}
The axial strain rate is the axial component of the <rate-of-strain tensor>. For axial <velocity> $w(z)$ it is $E=\partial w/\partial z$. In a uniform <uniaxial extensional flow>, $w=Ez$ and <incompressible flow> requires $u_r=-Er/2$; positive $E$ stretches the axial direction and contracts the transverse directions.