nouns
a sudden sharp noise
"the crack of a whip"; "he heard the cracking of the ice"; "he can hear the snap of a twig"
the act of cracking something
the process whereby heavy molecules of naphtha or petroleum are broken down into hydrocarbons of lower molecular weight (especially in the oil-refining process)
is a type of (narrower)
(chemistry) any process determined by the atomic and molecular composition and structure of the substances involved