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# Astronomy Chapter 4

### Astronomy

Question | Answer |
---|---|

speed | how far an object will travel in a certain amount of time |

velocity | how far and in what direction an object will travel |

acceleration | change in velocity |

acceleration of gravity | acceleration of a falling object in m per sec |

momentum | product of mass times velocity |

force | change applied to an object's momentum |

net force | overall force acting on an object |

angular momentum | circular momentum |

torque | twisting force that can change an objects angular momentum |

mass | amount of matter |

weight | force that a scale measures |

free-fall | falling without resistance |

weightlessness | in a state of free-fall |

Newton's First Law | An object moves at constant velocity if there is no net force acting upon it |

Newton's Second Law | Force = mass x acceleration (F=ma) |

Newton's Third Law | For any action, there is an equal and opposite reaction |

conservation of momentum | total momentum of interacting objects cannot change |

conservation of angular momentum | as long as there is no external torque, the total angular momentum of interacting objects cannot change |

conservation of energy | energy cannot appear out of nowhere or disappear into nothing |

kinetic energy | energy of motion |

radiative energy | energy carried by light |

potential energy | stored energy |

thermal energy | collective kinetic energy moving within a substance |

temperature | measures average kinetic energy of particles |

gravitational potential energy | how much mass an object has and how far it can fall |

mass-energy | energy contained in mass itself (E=mc^2) |

law of gravitation | Fg = GM1M2/d^2 |

bound orbit | ellipse |

unbound orbits | ellipse, parabola, hyperbola |

gravitational encounter | when two objects pass close enough to exchange orbital energy |

escape velocity | amount of energy needed by an object to clear a gravitational field of orbit |

tidal force | difference in gravitational forces that causes two tidal bulges |

tidal friction | tidal forces stretching the earth |

synchronous rotation | moon always shows the same face to Earth because of tidal friction |