**accuracy** |
the degree to which a measured value agrees with an accepted reference value for that measurement |

**base quantity** |
physical quantity chosen by convention and practical considerations such that all other physical quantities can be expressed as algebraic combinations of them |

**base unit** |
standard for expressing the measurement of a base quantity within a particular system of units; defined by a particular procedure used to measure the corresponding base quantity |

**conversion factor** |
a ratio that expresses how many of one unit are equal to another unit |

**derived quantity** |
physical quantity defined using algebraic combinations of base quantities |

**derived units** |
units that can be calculated using algebraic combinations of the fundamental units |

**dimension** |
expression of the dependence of a physical quantity on the base quantities as a product of powers of symbols representing the base quantities; in general, the dimension of a quantity has the form \(L^{a} M^{b} T^{c} I^{d} \Theta^{e} N^{f} J^{g}\) for some powers a, b, c, d, e, f, and g |

**dimensionally consistent** |
equation in which every term has the same dimensions and the arguments of any mathematical functions appearing in the equation are dimensionless |

**dimensionless** |
quantity with a dimension of \(L^{0} M^{0} T^{0} I^{0} \Theta^{e} N^{0} J^{0}\)= 1; also called quantity of dimension 1 or a pure number |

**discrepancy** |
the difference between the measured value and a given standard or expected value |

**English units** |
system of measurement used in the United States; includes units of measure such as feet, gallons, and pounds |

**estimation** |
using prior experience and sound physical reasoning to arrive at a rough idea of a quantity’s value; sometimes called an “order-of-magnitude approximation,” a “guesstimate,” a “back-of-the-envelope calculation”, or a “Fermi calculation” |

**kilogram** |
SI unit for mass, abbreviated kg |

**law** |
description, using concise language or a mathematical formula, of a generalized pattern in nature supported by scientific evidence and repeated experiments |

**meter** |
SI unit for length, abbreviated m |

**method of adding percents** |
the percent uncertainty in a quantity calculated by multiplication or division is the sum of the percent uncertainties in the items used to make the calculation |

**metric system** |
system in which values can be calculated in factors of 10 |

**model** |
representation of something often too difficult (or impossible) to display directly |

**order of magnitude** |
the size of a quantity as it relates to a power of 10 |

**percent uncertainty** |
the ratio of the uncertainty of a measurement to the measured value, expressed as a percentage |

**physical quantity** |
characteristic or property of an object that can be measured or calculated from other measurements |

**physics** |
science concerned with describing the interactions of energy, matter, space, and time; especially interested in what fundamental mechanisms underlie every phenomenon |

**precision** |
the degree to which repeated measurements agree with each other |

**second** |
the SI unit for time, abbreviated s |

**SI units** |
the international system of units that scientists in most countries have agreed to use; includes units such as meters, liters, and grams |

**significant figures** |
used to express the precision of a measuring tool used to measure a value |

**theory** |
testable explanation for patterns in nature supported by scientific evidence and verified multiple times by various groups of researchers |

**uncertainty** |
a quantitative measure of how much measured values deviate from one another |

**units** |
standards used for expressing and comparing measurements |