Key Terms

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