One thing that many people do not realize is that sound waves have physical properties and are therefore influenced by the environment in which they occur. In the vacuum of space, for instance, sounds cannot occur because, in a true vacuum, there is nothing to vibrate and cause a sound wave. The two most important physical qualities of sound are frequency and amplitude. Frequency is the speed at which a sound wave vibrates, and it determines the pitch of a noise. Higher frequency sounds have a higher pitch, like a flute or a bird chirping, while lower frequency sounds have a lower pitch, like a tuba or a large dog barking.
The amplitude of a sound wave can be thought of as the strength of the vibrations as they travel through the air, and it determines the perceived loudness of the sound. As you can see in Figure 1 , when the peak of the sound wave is smaller, the sound will be perceived as quieter.
If the peak is larger, then the sound will seem louder. It might even help to think of sound waves like waves in an ocean.
If you stand in still water and drop a pebble near your legs, it will cause a small ripple a tiny wave that does not affect you much. But if you stand in the ocean during stormy weather, the large incoming waves may be strong enough to knock you down!
Just like the size and strength of water waves, the size, and strength of sound waves can have a big effect on what you hear. Sound waves interact in fascinating ways with the environment around us. This is because it takes time for sound to travel from one point to another, and the movement of the sound source interacts with the frequency of the waves as they reach the person hearing it.
When the ambulance is far away, the frequency of the siren is low, but the frequency increases as the ambulance approaches you, which is a phenomenon known as the Doppler effect see Figure 2. Sound is not only affected by distance, however, but also by other objects. Think back to a time when someone was calling for you from another room.
You probably noticed that it was harder to hear them from another room than when he or she was right next to you. The distance between you is not the only reason a person is harder to hear when he or she is in another room.
The person is also harder to hear because the sound waves are being absorbed by objects in the environment; the further away the person calling you is, the more objects there are in between you two, so less of the sound waves eventually reach your ears. As a result, the sounds may appear to be quiet and muffled, even when the person is yelling loudly. Our ears are complex anatomical structures that are separated into three main parts, called the outer ear, middle ear, and inner ear.
The outer ear is the only visible part of the ear and is primarily used for funneling sound from the environment into the ear canal. From there, sound travels into the middle ear, where it vibrates the eardrum and three tiny bones, called the ossicles, that transmit sound energy to the inner ear. The energy continues to travel to the inner ear, where it is received by the cochlea. When the cochlea receives the sound, it amplifies the signal detected by these hair cells and transmits the signal through the auditory nerve to the brain.
While the ears are responsible for receiving sound from the environment, it is the brain that perceives and makes sense of these sounds. The auditory cortex of the brain is located within a region called the temporal lobe and is specialized for processing and interpreting sounds see Figure 3.
The auditory cortex allows humans to process and understand speech, as well as other sounds in the environment. To hear properly, the pressure on both sides of your eardrum must be equal. When you go up or down in elevation, the air pressure changes and you may feel a popping sensation as your ears adjust. They adjust thanks to the narrow Eustachian say: yoo-STAY-she-en tube that connects the middle ear to the back of the nose and acts as a sort of pressure valve, so the pressure stays balanced on both sides of the eardrum.
The vibrations from the middle ear change into nerve signals in the inner ear. The inner ear includes the cochlea say: KOH-klee-uh and the semicircular canals. The snail-shaped cochlea changes the vibrations from the middle ear into nerve signals. These signals travel to the brain along the cochlear nerve, also known as the auditory nerve. The semicircular canals look like three tiny connected tubes. It's their job to help you balance. The canals are filled with fluid and lined with tiny hairs.
When your head moves, the fluid in the canals sloshes around, moving the hairs. The hairs send this position information as signals through the vestibular say: veh-STIB-yuh-ler nerve to your brain.
The brain interprets these signals and sends messages to the muscles that help keep you balanced. When you spin around and stop, the reason you feel dizzy is because the fluid in your semicircular canals continues to slosh around for awhile, giving your brain the idea that you're still spinning even when you aren't. In this activity you'll learn a little bit more about your sense of hearing and how it works.
Background Most of us chiefly rely on eyesight, which is part of why we become so disoriented when forced to resort to a different sense. Nevertheless, our ears share a lot of important information about the world around us.
From the shout, "Fire! Sound travels through the air in waves. Your ears are specially equipped to receive and understand these waves. Each ear collects and channels sound waves, transforming them into vibrations. Within your inner ear tiny hair cells respond to these vibrations and send signals that your brain can decode and interpret as a variety of sounds.
But why exactly do we have two ears instead of just one? Try this activity and find out. Record or draw the direction your partner is facing and ask your partner to remain in that spot throughout the activity. Your partner will then guess where you are left, right, in front, behind and how far away you are standing.
Say your partner's name in a normal speaking voice. Ask him or her to guess where and how far away you are standing. Did your partner guess where you were standing? Try this from different lines all over the room and record your partner's guesses. Is your partner better at guessing when you're close by or far away? How well does your partner guess distance? What about direction?
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