Tables and constants in physics

Physics is an empirical science, and its formulas only become useful when paired with reliable numerical data. That data falls into three broad kinds: the fundamental constants of nature, the system of units used to express measurements, and tabulated properties of specific materials and substances. Handbooks and online databases bring these together so that a calculation made in one laboratory can be checked and reproduced in another.

Engineering fundamentals draw heavily on material property tables. The electrical conductivity and resistivity of a metal determine how well it carries current and how much it heats up; copper and aluminium sit near the top of the conductivity ranking, while glass and most plastics are insulators. Acoustic properties such as the speed of sound and the density and stiffness of a medium govern how sound and vibration travel, which matters for design in fields from architecture to ultrasonics. Thermal and mechanical tables list densities, expansion coefficients and strength values.

At the atomic scale, reference data become finer grained. Atomic weights give the average mass of each element's atoms relative to a fixed standard, and underlie every calculation of chemical amounts. Atomic spectroscopic data catalogue the precise wavelengths of light absorbed and emitted by atoms, which serve both as fingerprints for identifying elements and as tests of atomic theory. Studies of condensed matter add information on how large numbers of atoms behave together in solids and liquids. Because so many quantities share standard symbols and abbreviations, glossaries of scientific and technical notation accompany the tables and help readers interpret them correctly.

Frequently asked questions

What is electrical resistivity?

Resistivity is a material property that measures how strongly a substance opposes the flow of electric current; it is the inverse of conductivity and is independent of the sample's size.

What does atomic weight mean?

Atomic weight is the average mass of an element's atoms, weighted by the natural abundance of its isotopes and expressed relative to a fixed reference standard.

How is the speed of sound related to the medium?

Sound travels faster in stiffer, denser media; it moves much faster through steel or water than through air, and acoustic tables list these values for many materials.