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# Physics Definitions

### Physics Definitions and Laws

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

Physical Quantity: | One that can be measured, or calculated, and expressed in numbers. |

Scalar Quantity: | One with magnitude only. It has no directional component. |

Vector Quantity: | One with both magnitude and direction. |

Distance: | The distance between two points is a measure of how far one point is from the other. |

Time: | Is used to measure the duration of events, to put them in sequence or to measure the interval between them. |

Speed: | The distance traveled per unit time. |

Displacement: | The distance in a given direction. |

Velocity: | The rate of change of displacement with respect to time. |

Acceleration: | The rate of change of velocity with respect to time. |

Mass: | The measure of amount of matter in a body. |

Momentum: | The product of mass and velocity. (p=mv) |

Force: | A force is that which can cause acceleration. |

Newton's First Law of Motion: | A body will remain at rest or continue moving at constant velocity unless acted upon by an unbalancing force. |

Newton's Second Law of Motion: | The rate of change of momentum is proportional to the applied force and takes place in the direction of force. |

Newton's Third Law of Motion: | For every action there is equal and opposite reaction. The action and reaction do not happen on the same body. |

Acceleration Due to Gravity: | The acceleration experienced by a body in free fall within the gravitational field of a massive body. (g=GM/R^2) |

Weight: | A force equal to the product of mass and acceleration due to gravity. (W=mg) |

Newton's Law of Universal Gravitation: | F=Gmm/d^2 |

Moment of Force: | The force multiplied by the perpendicular distance to the fulcrum. (M=Fd) |

A Fulcrum: | A fixed point about which a rigid body (called a level) is free to rotate. |

Levers: | A rigid body that is free to rotate about a fixed point. |

Couples: | A pair of equal and opposite forces whose lines of action do not coincide. |

Torque: | The torque of a coupe is equal to the magnitude of one of the forces multiplied by the distance between them. (T=Fd) |

First Condition for Equilibrium: | The vector sum of the forces in any direction is zero. Forces up = Forces down. Forces left = Forces right. |

Second Condition for Equilibrium: | The vector sum of moments about any point is zero. The sum of the clockwise moments about any point is equal to the sum of the anticlockwise moments about that point. (Law of the lever) |

Density: | Mass per unit volume. (p=m/v) |

Pressure: | The force per unit area. |

Buoyancy: | The upward force on a body that is wholly or partially immersed in a fluid. |

Archimedes Principle: | When a body is wholly or partially immersed in a fluid, it experiences an upthrust equal to the weight of the fluid displacement. |

Law of Floatation: | The weight of a floating body is equal to the weight of the fluid displacement. |

Boyle's Law: | Pressure is inversely proportional to volume for a fixed mass of gas at constant temperature. (p=1/V) |

Work: | The product of force and displacement. (W=Fs) |

Energy: | The ability to do work. |

Kinetic Energy: | The energy a body has due to its motion. (Ek=0.5mv^2) |

Potential Energy: | The energy a body has to its position or condition. (Ep=mgh) |

Power: | The rate at which work is done. (P=W/t) |

Power Efficiency: | A measure of how good a machine is at converting energies without waste. (%Efficiency=(P.Output x 100)/P.Input) |