### Key Terms

- 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 ${\text{L}}^{\text{a}}{\text{M}}^{\text{b}}{\text{T}}^{\text{c}}{\text{I}}^{\text{d}}{\text{\Theta}}^{\text{e}}{\text{N}}^{\text{f}}{\text{J}}^{\text{g}}$ 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 ${\text{L}}^{0}{\text{M}}^{0}{\text{T}}^{0}{\text{I}}^{0}{\text{\Theta}}^{0}{\text{N}}^{0}{\text{J}}^{0}=1;$ 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