Every object has a natural resonance frequency: a preferred speed for vibrating back and forth. A bass drum's vibrations produce a low-frequency sound wave. A piccolo's vibrations produce a higher frequency wave.

Even tiny objects like atoms have natural frequencies. Atoms absorb or emit energy only at specific frequencies. Scientists use these frequencies as a kind of fingerprint for identifying atoms. Astronomers determine the elements in stars by studying the frequencies of light they emit. Chemists identify compounds in materials by heating them and studying the frequencies of light emitted or absorbed.