What is Sound?

A drummer bangs on a bass drum. Sam, standing nearby, hears BOOM! How does banging on the drum turn into the sound BOOM? Sounds are vibrations, and the drum-head’s back-and-forth vibrations create pressure waves in the air that set Sam’s eardrums, just inside his ears, into vibration. The magic of sound happens deeper inside Sam’s ears in a hollow tube-like structure called the inner ear or cochlea. Imagine that you’ve shrunk yourself so small that you can look into this tube. When you peek inside, you see thousands of tiny hairs lined up in rows. Suddenly, the drummer bangs the drum! You feel the vibrations, and then you see something spectacular – the hairs are moving back and forth in time with the vibrations, and every movement is creating electrical signals! These signals are sent down the auditory nerve towards the brain and a fraction of a second later, when they reach the hearing areas in the brain, Sam hears BOOM! What makes some vibrations create a drum’s low-pitched BOOM and others create a bird’s high-pitched tweet? Slow vibrations create low pitches and faster vibrations create high pitches, so the hairs vibrate more slowly for BOOM and faster for tweet. But sound is more than BOOM and tweet. You create sounds when talking with friends or playing music. Music is really amazing, because when the tiny hairs vibrate back and forth to music, electricity reaches the brain’s hearing areas, plus other brain areas that make you move and that make you feel emotions like happy or sad. So sounds are vibrations that make you hear, and might also make you feel like tapping your feet, dancing, crying, or even jumping for joy. Pretty amazing, what tiny hairs vibrating inside the ear can do!