1 Units and Measurement
1 Chapter Review
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 LaMbTcIdΘeNfJgLaMbTcIdΘeNfJg 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 L0M0T0I0Θ0N0J0=1;L0M0T0I0Θ0N0J0=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
- pre