Sound travels in waves, much like those that roll across the ocean, to give our ears information which we may or may not understand. These sound waves are very much like those that light uses, too, whether it’s the (mostly) steady flow of light from the Sun or spectacular 4th of July fireworks which combine light and sound for an amazing night of excitement. But sound waves are also used for communication amongst humans and amongst other life forms to tell about important things (Predator coming!) and not so important things (the bus is late—again!).
When we cannot see, sound can be used to know where we are and to help us find our way. This can be as easy as listening for the sound of traffic if you are lost in the woods or as sophisticated as using sonar to find sunken treasure or enemy vessels. There are certain animals, such as bats, that don’t rely on their sense of sight very much at all. Living mostly in the dark, they use their own sonar to know where they are.