Sound

physics · music · senses

It's a wave. Sound travels as waves of pressure pushing through air, water, or solid stuff. It needs a material to move through, which is why there's no sound in empty space.

Your hearing range. Human ears can hear frequencies from about 20 Hz (super low) up to 20,000 Hz (super high). Sounds above that are called ultrasound, which dogs and bats can hear but we can't.

Music and language. Sound is the secret behind music, talking, and singing. Different frequencies make different pitches, which is how a tuba sounds deep and a whistle sounds high.

Doctors use it. Ultrasound machines send sound waves into the body and listen to the echoes to make pictures, like peeking inside without surgery.