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# Physics Definitions

### Module 2 Forces in action

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

Newton's second law | net force = mass x acceleration |

The newton | Unit of force. 1N is the force that gives a mass of 1kg an acceleration of 1m/s^2 |

Drag | The resistive force that acts on a body when it moves through fluid |

Weight | The gravitational force acting on an object measured in Newtons |

Terminal Velocity | The velocity at which an object's drag equals to it's accelerating force. therefore there is no resultant force and zero acceleration |

Equilibrium | When the net force and net moment on an extended object is zero |

Centre of gravity | this is the point where the entire weight of an object appears to act |

Triangle of forces | If three forces acting at a point can be represented by the sides of a triangle, the forces are in equilibrium |

Couple | This is a pair of forces that tends to produce rotation only. They are two forces that are equal in size but act in opposite directions but not in the same straight line |

Torque of couple | The turning effect of a couple measured in Nm. |

Moment of a force | The turning effect due to a single force. Calculated from the force multiplied by the perpendicular distance from a given point. |

Principle of moments | For a body rotational equilibrium the sum of the clockwise moments equals to the sum of the anticlockwise |

Density | the mass per unit volume |

Pressure | Force per unit area |

Thinking distance | The distance travelled from seeing the need to stop to applying the brakes |

Braking distance | The distance travelled by a vehicle whilst decelerating to stop |

Stopping distance | The distance a vehicle travels whilst decelerating to stop. The sum of the thinking distance and braking distance |

Crumple zone | An area of a vehicle designed to increase the distance over which the vehicle decelerates and so reduce the average force acting |