Now you hear it, now you don’t
A ticking clock sounds loud when you put your ear close to it. But as
you walk away, the ticking gets softer and softer—until you can’t hear
the clock at all. Why does the sound get softer?
The ticking you hear is made by the moving parts of the clock. These
parts vibrate with a fast, back-and-forth motion. This back- and-forth
motion is energy—tiny pushes and pulls. The pushes and pulls make the
air around the clock move—they push the air molecules together into
waves.
Sound waves are much like the waves you make when you drop a rock into a
quiet pond. The waves in the water spread out in all directions. The
sound waves from the clock also spread out in all directions. They move
through the air to your ear, and you hear the ticking.
The sound waves are strongest where they are made—close to the
vibrating clock. So when you stand next to the clock, the ticking you
hear is loud.
But as the sound waves spread out through the air, they grow weaker and
weaker, just as the waves in water do. So as you move away from the
clock, the ticking gets softer.
By the time the sound waves have traveled across the room, the air is
hardly moving at all. The pushes and pulls are too tiny for your ears to
pick up—so you no longer hear the sound of the ticking clock.
