Why does laugh make an F sound?

Laugh makes an F sound in its spelling and pronunciation because of its historical evolution from Old English. The word laugh comes from Old English hlaehhan, which had a guttural ch sound similar to Scottish loch, pronounced as voiceless velar fricative. Over centuries, that guttural ch sound shifted in English to an F sound in some words, a process called pronunciation change. In Middle English, laugh was pronounced with that guttural sound, but by Modern English, the gh cluster came to be pronounced as F, as in laugh pronounced laf, enough pronounced enuff, and cough pronounced coff. The spelling kept gh to reflect older pronunciation, but sound became F. When you actually laugh, the ha ha sound does not contain F, but the word itself ends with F sound due to this historical sound change. So the F in laugh is not from the sound of laughing itself, it is a linguistic artifact of how Old English hlaehhan evolved, with gh becoming F in pronunciation while spelling stayed. This is why laugh, draft, and tough have F sound.