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# Chapter 4, 5, 6

### Revise Forces, Moments, Centre of gravity, Levers and Pressure

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

What is the difference between mass and weight? | Mass is the mount of matter in an object, weight is mass due to gravity. |

What is the unit of weight? | Kilogram, Kg. |

How do you calculate a person’s weight? | Using a mass balance. |

Why do people have different weights on the moon and in outer space? | There is less gravity in those places. |

What is the formula for a moment of a force? | Moment of force = distance from center Multiplied by force applied. M=RxF |

What is a lever? | A lever is a beam or rigid rod pivoted at a fixed hinge, or fulcrum |

Define the law of the lever. | If the distance from the fulcrum to where the input force is applied is greater than the distance from fulcrum to where the output force is applied, then the lever amplifies the input force |

What is the center of gravity? | The point at which all the mass in an object can balance on a single point. |

What is stable, neutral and unstable equilibrium? | Stable: Where the center of gravity is below the resting point. Neutral: Where the center of gravity and restig point are the same height. Unstable: Where the center of gravity is above the resting point. |

What is pressure? | Force per unit area. |

What units is pressure measured in? | Newtons per Meter square. N/m2 |

What is the relationship between pressure, force and area? Give the formula for this relationship. | Force, pressure and area all change each others outcome. Force = Pressure x Area. |

How does pressure vary with depth in liquids? | It increases. |

What is atmospheric pressure? | It is the pressure of the air pressing against us at sea level. |

How does atmospheric pressure vary with height? | It decreases. |

Where is pressure greatest – at the top of a mountain or at sea level? | Sea level. |

How can you measure pressure? | Using a barometer. |

What is an isobar? | An Isobar is a line of equal or constant pressure on a graph, plot, or map. |

When the pressure is high what will our weather be like? | Clear and sunny. |

When the pressure is low what will our weather be like? | Windy and raining. |

When the isobars are very close together on a weather chart what does this mean for the weather? | It should be clear and sunny. |