Newton's second law (variable-mass system)

Description

Variable-mass systems, (like a rocket burning fuel and ejecting spent gases), are not closed and cannot be directly treated by making mass a function of time in the second law. The correct equation of motion for a body whose mass varies with time by either ejecting or accreting mass is obtained by applying the second law to the entire, constant-mass system consisting of the body and its ejected/accreted mass.

Related formulas

Variables

FNet force applied (N)
uVelocity of the escaping or incoming mass (m/s)
dmMass change (kg)
dtTime change (s)
mTotam mass of the body (kg)
dvVector of velocity (m/s)