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# Physics Mechanics

### Definitions

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

Define Displacement | The distance moved in a stated or given direction. It is a Vector. |

Define Instantaneous speed | The rate of change of distance or the distance travelled per unit time, at a given moment. Scalar. |

Define Average Speed | The total distance travelled divided by the total time taken. Scalar. |

Define Velocity | The displacement per unit time or the rate of change of displacement. Vector. Instantaneous velocity is the rate of change of Displacement at a particular moment of time. |

Define Acceleration | The rate of change of velocity or the increase in velocity divided by the time taken. vector. |

Define Newton | The force that cause a 1 kg mass to have an acceleration of 1 metre per second squared. |

State what is meant by the weight of an object | The gravitational force acting on it. Vector. |

State the factors that affect magnitude of the drag force. | Velocity, roughness of surface, cross-sectional area and shape. |

Explain the term terminal velocity | The velocity of a falling object reached when the resultant force on it is zero. The drag force is equal to the weight therefore no resultant force therefore no force to create acceleration. |

State what is meant by centre of gravity | The point wher the entire weight of the object appears to act. |

Define the moment of a force | The force multiplied by the perpendicular distance from a stated point. |

Define the torque of a couple | The turning effect of the couple and this is shown by the force of one of them multiplied by the perpendicular distance between them. |

Define A couple | A pair of equal and parallel but opposite forces which tend to produce rotation only. |

Equilibrium | A body in equilibrium must be acted upon by no resultant force in any direction and no net moment about any point. |

Define Thinking Distance | The distance travelled by the vehicle during the driver's reaction time. |

Define Braking Distance | The distance travelled when the brakes are applied. |

Define Stopping Distance | The total distance travelled whilst thinking and braking. |

Define work done by a force | The force acting multiplied by the distance moved by the force in the direction of the force. |

Define the joule | The work done when a force of 1 newton moves its point of application a distance of 1 metre in the direction of the force. |

Energy | Energy is the stored ability to do work |

Conservation of energy | In any closed system energy may be converted from one form to another but can neither be created nor destroyed. Work done = energy transferred. |

Define power | the rate of doing work or the rate of transferring energy. |

Define The watt | A rate of doing work or rate of enery conversion of 1 joule per second. |

Define Stress | The force per unit cross-sectional area. |

Define Strain | The fractional increase in length or extension per unit length. |

Define Young Modulus | The ratio of stress to strain for a given material. |

Define Ultimate tensile strength or breaking stress or ultimate tensile stress. | the maximum stress that can be applied to a material before it will break. |

Define elastic deformation | A temporary change in shape of an object so that when the force causing it is removed it returns to its original shape. Shown by intial straight line on a stress-strain graph. |

Define Plastic deformation | A Permanent change in shape produced by the application of a force so that the change in shape remains when the force is removed. It is any extension beyond its elastic limit. |

Ductile | A material that can be drawn out. It exhibits plastic behaviour. Extension can be considerable often with reducing stress. In ductile materials the layers of atoms slide over each other. |

Brittle | A material that does not show any plastic behaviour. It will not normally extend much and will break suddenly without atoms within it changing there relative positions. Will hardly streth or deform before they break. |

Stiff | A material that resists extension, so a large force is needed for a small increase in length. It will have a large young modulus. |

Strong | A material that will need a large force or large stress to break it. It has a high ultimate tensile strength. |

Tough | A material that will resist fracture from an impact load. |