Figure 20.23: This outdoor fruit market stimulates all the senses—sight, sound, smell, taste,
and touch. ( 25 )
Hearing and Balance
What do listening to music and riding a bike have in common? It might surprise you to
learn that both activities depend on your ears. Theearsare sense organs that detect sound.
They also sense the position of the body and help maintain balance.
Hearing
Hearingis the ability to sense sound. Sound travels through the air in waves, much like
the waves you see in the water inFigure20.24and the light waves described in Lesson 2.
Sound waves in air cause vibrations inside the ears. The ears detect the vibrations.
Figure 20.24: Sound waves travel through the air in all directions away from a sound like
waves traveling through water away from where a pebble was dropped. ( 13 )
What the human ear looks like is shown in Figure20.25. As you read about it below,
trace the path of sound waves through the ear. You can also see an animation of the ear
sensing sound athttp://www.sumanasinc.com/webcontent/animations/content/sound-
transduction.html.
Assume a car horn blows in the distance. Sound waves spread through the air from the horn.
Some of the sound waves reach your ear. The steps below show what happens next. They