# 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

F | Net force applied (N) |

u | Velocity of the escaping or incoming mass (m/s) |

d_{m} | Mass change (kg) |

d_{t} | Time change (s) |

m | Totam mass of the body (kg) |

d_{v} | Vector of velocity (m/s) |