= Zero-relative-velocity mass shedding
{title2=$q\dot v=F_{\rm ext}$}
When matter leaves a moving body with zero instantaneous relative <velocity>, it carries the body's current <momentum> per unit mass but creates no additional recoil term. A short-interval <momentum> balance including the newly released material gives $q\dot v=F_{\rm ext}$ for the remaining body's mass $q(t)$. The expression $\frac d{dt}(qv)=F_{\rm ext}$ omits the outgoing momentum flux. Nonzero relative ejection <velocity> instead produces the thrust term of the <rocket equation>.
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