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# Physics Unit 4

### Gravity, Rotational, & Projectile Motion

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

tangential speed | the linear speed tangent to a curved path, such as in circular motion |

rotational speed | the number of rotations or revolutions per unit of time; often measured in rotations or revolutions per second or minute |

rotational inertia | the property of an object to resist any change in its state of rotation; if at rest, tends to stay at rest OR if rotating, tends to stay rotating unless acted upon by an external net torque |

torque | the product of force & lever-arm distance, which tends to produce or change rotation |

center of gravity (CG) | the average position of weight or the single point associated with an object where the force of gravity can be considered to act |

center of mass (CM) | the average position of the mass of an object |

equilibrium | the state of an object in which it is not acted upon by a net force or a net torque |

centripetal force | a force directed TOWARD a fixed point, usually the cause of circular motion |

centrifugal force | an OUTWARD force apparent in a rotating frame of reference; fictitious in the sense that it is not part of an interaction but is a result of rotation, with no reaction-force counterpart |

linear momentum | the product of the mass of an object & its linear velocity |

angular momentum | the product of a body's rotational inertia & rotational velocity about a particular axis |

Conservation of Angular Momentum | when no external torque acts on an object or a system of objects, no change of angular momentum can occur; the angular momentum before an event equals the angular momentum after an event |

Law of Universal Gravitation | every body in the universe attracts every other body with a force that, for two bodies, is directly proportional to the product of their masses & inversely proportional to the square of the distance between their centers |

Inverse-Square Law | a law that relates the intensity of an effect to the universe square of the distance from the cause; gravity follows this law |

weight | the force that an object exerts on a supporting surface which is often due to the force of gravity |

weightless | being without a support force, as in free fall |

Spring Tides | high or low tides that occur when the sun, earth, & the moon are all lined up; makes the high & low tides higher & lower than average |

Neap Tides | tides that occur when the moon is midway between new & full, in either direction; makes high tides lower than average & low tides higher than average |

gravitational field | the influence that a massive body extends into the space around itself, producing a force on another massive body; measured in N/kg |

black hole | a concentration of mass that results from gravitational collapse, near which gravity is so intense that not even light can escape |

projectile | any object that moves through the air or through space under the influence of gravity |

parabola | the curved path followed by a projectile under the influence of ONLY constant gravity |

satellite | a projectile or small celestial body that orbits a larger celestial body |

ellipse | the oval shaped path followed by a satellite |

circle | a special kind of ellipse where the foci are together at one point |

escape speed | the speed that a projectile must reach to escape the gravitational influence of earth or of another celestial body to which it is attracted |

Kepler's First Law | The path of each planet around the sun is an ellipse with the sun at one focus |

Kepler's Second Law | the line from the sun to any planet sweeps out EQUAL areas of space in EQUAL time intervals |

Kepler's Third Law | the square of the orbital period of a planet is directly proportional to the cube of the average distance of the planet from the sun |

Created by:
vahajuddin