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# Physics ch. 16-17

### Motion and force

Term | Definition |
---|---|

motion | distance from another object is changing |

reference point | a place or object used for comparison |

SI | international system of units (metric system) |

speed | the distance an object travels in a certain amount of time |

speed formula | S=D/T |

velocity | speed and direction of an object |

acceleration | the process of increasing speed, decreasing speed or changing direction |

acceleration formula | A=final speed-initial speed/ time |

force | a push or a pull |

newton | the SI unit of measurement for force |

unbalanced force | causes an object to move |

balanced force | an object will not move because there is equal pressure applied in both directions |

friction | the force applied when two surfaces rub against each other |

static friction | friction that acts on an object that is not moving |

sliding friction | friction that occurs when two solid surfaces slide over each other |

rolling friction | friction that occurs when an object rolls across a surface |

fluid friction | friction that occurs when a solid object moves through a fluid |

gravity | a force that pulls objects towards each other |

mass | the measure of the amount of matter in an object |

weight | the measure of the gravitational force exerted on an object |

free fall | when the only force acting on an object is gravity |

air resistance | objects falling through air experience this type of fluid friction |

terminal velocity | the fastest something can fall |

Inertia | the tendency of an object to resist a change in motion |

Newtons first law | an object at rest will stay at rest and an object in motion will stay in motion unless acted upon by an outside force |

Newtons second law | force equals mass times acceleration |

Newtons third law | for every action there is an equal and opposite reaction |

momentum formula | momentum=mass x velocity |

Law of conservation of momentum | the total momentum does not change in a collision unless acted upon by an outside force. |