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# A level ocr 5.4

### Gravitational fields

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

Escape velocity | The minimum launch required to move an object from a point in a gravitational field to a point a infinity. |

Geostationary Orbit | An equatorial orbit with a period of 24h/1day/same as Earth, the satellite moves from east to west. |

Gravitational field lines | Shows the shape of the field. The direction of the line is the direction in which a small mass would move |

Gravitational Field Strength | Force per unit mass |

Gravitational potential | Potential energy is equal (in magnitude, but negative) to the work done in bringing unit mass ne from infinity to the point concerned. We assume at infinity the gravitational potential is 0 J/kg |

Gravitational potential energy | For a radial field around a point or spherical mass M = mass of the object x gravitational potential Note near the earth's surface we assume that the gravitational field strength is constant so GPE = mgh |

Kepler’s Third Law | The cube of the planets distance (from the Sun) divided by the square of the (orbital) period is the same (for all planets) |

Newton’s Law of Gravitation | Force is proportional to the product of the masses and inversely proportional to the square of their separation |

The period of an object describing a circle | The time taken to complete one full orbit. |