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Why do the sounds /f/ and /v/ differ even though the lips and teeth are positioned similarly?

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Diagram of a human head in profile showing the location of vocal organs and possible places of articulation for speech sounds, with labels for lips, teeth, tongue, palate, uvula, pharynx, and vocal cords, and numbered regions corresponding to types of articulation such as bilabial, alveolar, and velar.
phonetics Diagram depicting the location of human vocal organs and possible places of articulation used for speech.

In phonetics, the sounds /f/ and /v/ are both classified as fricatives, meaning they are produced by narrowing the vocal tract to create audible friction as air passes through. While they share the same place of articulation—specifically, they are labiodental sounds produced by positioning the teeth against the lips—they differ fundamentally due to the presence or absence of voice.123

The sound /v/ is a voiced consonant, meaning the vocal cords are held taut and vibrate as air passes through the larynx. In contrast, /f/ is a voiceless consonant, produced without this vibration of the vocal cords. Because the vocal cords do not vibrate during the production of /f/, it lacks the periodic waveform and the additional acoustic energy associated with voicing, making it distinct from the voiced /v/.324