observation that yields descriptive, nonnumerical results

quantitative observation

observation that yields meaningful, numerical results

quantum (singular form of quanta)

small unit of energy

quantum mechanics

the branch of physics that deals with the behavior of matter at the atomic and subatomic level

quantum numbers

four special numbers that completely describe the state of an electron in an atom

quantum theory

the theory that energy can only exist in discrete amounts (quanta)

quark

physical particles that form one of the two basic constituents of matter; various species of quarks combine in specific ways to form protons and neutrons, in each case taking exactly three quarks to make the composite particle