**Operationally Defined Quantities:**

- There are only a few fundamental units from which the units of all physical quantities in science can be expressed.
**The fundamental units are defined by a measuring process.**- The meaning of a fundamental quantity is equivalent to the process one uses to associate a number with the current state of that quantity.
- A number/answer without any units has no physical meaning.

Quantity |
Symbol |
SI Units |

Length, Distance | _{} |
m -meters |

Time | _{} |
s- seconds |

Mass | _{} |
kg - kilograms |

Temperature | _{} |
K - degrees Kelvin |

Angle | _{} |
rad - radians |

Charge | _{} |
C - Coulombs |

- Derived physical quantities (which are the majority of quantities) are defined by a mathematical expression involving either the fundamental quantities or other derived quantities.

Quantity |
Symbol |
Definition |
SI Units |

Velocity, Speed |
_{} |
_{} |
m/s |

Acceleration |
_{} |
_{} |
m/s^{2} |

Energy: Kinetic Potential |
_{} |
_{} |
J -Joules J = kg m ^{2}/s^{2 } |

Force | _{} |
_{} |
N - Newton |

Momentum | _{} |
_{} |
kg m/s |

Volume | _{} |
_{} |
m^{3} |

Density |
_{} |
_{} |
kg/m^{3} |

Pressure |
_{} |
_{} |
Pa -Pascal Pa = N/m ^{2 } |

- Note that the generic units (i.e. units expressed only in terms of the fundamental units) of a derived quantity follows from the mathematical definition of the derived quantity.

- Many important derived quantities have been a special name like the energy - Joule. None-the-less, these "brand" names are just pointers to an expression of the fundamental units, Joule = km m
^{2}/s^{2}.