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# Physics Defintions

### AS Physics definitions

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

Define Newton | Unit of force. The force that causes an object of mass 1kg to accelerate at 1m/s^2. |

Define Weight | the force on the object due to gravity. |

Define Scaler | A physical quantity with magnitude (size), but not direction, e.g. speed, distance, pressure, potential difference, density and energy. |

Define Vector | A physical quantity with magnitude (size) and a direction, e.g. velocity, acceleration and force. |

Define displacement | The distance travelled in a particular direction. Therefore a vector. |

Instantaneous speed | The speed of an object given at a certain moment in time. |

Define average speed | Measure of the total distance travelled in a unit of time. |

Define velocity | Displacement divided by time. |

Define acceleration | The rate of change of velocity. |

Define terminal velocity | The velocity at which an objects drag is equal to its accelerating force. Therefore there is no resultant force and zero acceleration. |

Define Newtons Second Law | Net Force = mass x acceleration. |

Define drag | The resistive force that acts on a body when it moves through a fluid. |

Equilibrium | When the net force or resultant force is equal to zero. |

Define centre of gravity | The point where the entire weight of an object appears to act. |

Define couple | A pair of forces equal to each other that tend to produce a rotation only. |

Define torque of a couple | The turning affect due to a couple. |

Define moment of a force | The turning effect due to a single force, calculated from the force x the perendicular distance from a given point. |

Define thinking distance | The distance travelled from seeing the need to stop (hazard) to applying the brakes. |

Define braking distance | The distance travelled by a vehicle whilst decelerating to a stop. |

Define stopping distance | The distance a vehicle travels while decelerating to a stop. The sum of the thinking distance and the braking distance. |

Define work done | The force x distance moved in the direction of the force. |

Define joule | Unit of energy. 1J is the work done when a force of 1N moves an object 1m in the direction of the force. |

Define conservation of energy | States that no energy can be created or destroyed, only converted from one form into another. |

Define power | The rate of work done. |

Define the watt | The unit of power. 1W is 1J of energy transferred per second. |

Define efficiency | The ratio of useful output energy to total input energy. Useful output divided by total input x 100(%). |

Define tensile force | Usually two equal and opposite forces acting on a wire in order to stretch it. |

Define compressive force | Two or more forces that have the effect of reducing the volume of the object on which they are acting or reducing the length. |

Define extension | The change in length of an object when subjected to a tension. |

Define elastic limit | The point at which elastic deformation becomes pastic deformation. |

Define elastic deformation | The object will return to its original shape when the deforming force is removed. |

Define plastic deformation | The object will not return to its original shape when the deforming force is removed. It becomes permenantly deformed. |

Define ductile material | Materials that have a large plastic region and can therefore be drawn into a wire, e.g. copper. |

Define brittle material | A material that distorts very little, even when subject to a large stress and does not exhibit any plastic deformation, e.g. concrete. |

Define limit of proportionality | The point at which an object no longer obeys Hookes Law. |

Define Hookes Law | The extension of an elastic body is proportional to the force that causes it up to the limit of proportionality. |

Define the force constant | The force per unit extension or compression. |

Define elastic potential energy | The energy stored in a stretched or compressed object, e.g. a spring. |

Define stress | The force per cross-sectional area. |

Define strain | The extension per unit length. |

Define Young's Modulus | The ratio between stress and strain. Stress divided by strain. |

Define ultimate tensile strength | The maximum tensile force that can be applied to an object before it breaks. |