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# Physics ch10

### Pressure, Gravity and Moments

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

Density | The density of a substance is its mass per unit volume. D= M/V |

Unit of Density | Kg m-3 kilograms per cubic metre |

Pressure | Pressure is the force per unit area. P= F/A |

Unit of pressure | Pascal or 1 Newton per square metre |

Archimedes Principle | When an object is partially or completely immersed in a fluid it experiences an upthrus t equal in magnitude to the weight of the fluid displaced. |

The law of flotation | The weight of a floating body is equal to the weight of the fluid it displaces. |

Boyle's Law | At a constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure. |

Newton's law of Universal Gravitation | Any two point masses in the universe attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. F= Gm1m2/d2 |

Moment of a force | The moment of a force about an axis is equal to the magnitude of the force multiplied by the perpendicular distance from the axis to the line of action of the force. M= F x d |

Unit of moment | Nm Newton metre |

If a body is in equilibrium: | The vector sum of the forces in any direction is 0. The sum of the moments about any point is 0 |

Couple | Two parallel forces with the same magnitude acting in opposite directions. |

Moment of a couple (torque) | T = Fd |