WAVE BEATS

LET TWO WAVES[SOUND] OF SLIGHTLY DIFFERENT FREQUENCIES MEET. 1.WHEN CREST AND CREST, TROUGH AND TROUGH MEET, THEY REINFORCE EACH OTHER. 2. WHEN CREST AND TROUGH MEET, THEY DESTROY EACH OTHER. AS TWO WAVES TRAVEL SIMULTANEOUSLY, THE INSTANTS 1 AND 2 ARISES ALTERNATIVELY. HENCE WAVE RISE AND FALL. SO IS THE SOUND. ---BEATS