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# EK Physics 2

### Force

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

mass | quantitative measure of an object's inertia, larger mass means it will resist change in motion more, standard unit is in kg |

inertia | tendency of an object to remain in its present state of motion |

weight | gravitational force an object experiences when near a much larger body, standard measure is newtons (N) |

center of mass | single point were all of the mass of the system can be considered as concentrated |

center of gravity | single point at which the force of gravity can be applied to the entire mass |

four forces in nature | 1. strong nuclear force 2. weak nuclear force 3. gravitational force 4. electromagnetic force |

Newton's first law | law of inertia: an object in state of rest or in state of motion will tend to remain in that state unless it is acted upon by a net force |

Newton's second law | F = ma |

Newton's third law | for every action, there exists an equal and opposite reaction |

Newton's law of universal gravitation | every mass in the universe exerts an attractive force on every other mass in the universe, and that the force is proportional to both the masses m1 and m2 and inversely proportional to the square of the distance r between them F = G*m1*m2/r^2 |

normal force on an inclined plane | mgcos(theta) |

gravitational force down the inclined plane | mgsin(theta) |

circular motion | object moving in a circle will have instantaneous velocity where magnitude is the same but the direction changes at constant rate (centripetal acceleration) |

centripetal acceleration | points towards the center of the circle ac = v^2/r |

centripetal force | Fc = mv^2/r must be created by gravity, electromagnetic, or contact forces; always points to the center of the circle |

friction | caused by attractive molecular forces btw contiguous surfaces, opposes relative motion btw contiguous surfaces, two types - static and kinetic, ALWAYS PARALLEL TO CONTACT SURFACE |

static friction | force opposing motion when 2 contiguous surfaces are not moving relative to each other |

kinetic friction | force resisting motion once the 2 contiguous surfaces are sliding relative to each other |

tension | force acting thru a flexible object with no mass (like a string or rope), requires equal force at both ends of the rope and the tension is equal to only one of the forces, not both |

Hooke's law | describes force applied by most objects against a deforming force, ex: spring F = -k*(x2-x1) |