Every language has differences in intonation of utterances depending on the latter’s content and purport. The basic divide is between questions and statements, hence interrogative intonation is invariably different from declarative intonation, although a relatively new phenomenon in American English––Valley-girl patois ––tends to usurp the declarative mode by substituting the interrogative at the end of every clause, including sentence-final.
In languages as disparate as Russian, Japanese, and English (to name just three that happen to be Y-H-B’s native languages) interrogative intonation comports a rise that is lacking in declarative intonation, and this suprasegmental feature can be understood as an icon of the difference in meaning between the two types of clauses or sentences uttered with these two intonations. Interrogatives always come with a rise in the voice, whether or not attended by a minimal fall, whereas declaratives always lack this rise even though they may have a perceptible but non-significant fall across the final portion of the utterance. Final position in the clause, sentence, or utterance is decisive for interrogative meaning except where the rise occurs on interrogative words (like ‘how’, why’, ‘when’) that come before final position.
The intonational universal determining rises and falls has to do with how all languages construe questions. The obligatory rise in interrogatives is an icon of the unsettled state of questions vis-à-vis statements: the former figuratively “hang in the air” (cf. R висят в воздухе), whereas the latter are “grounded.”