Sound waves are vibrations moving through the air. How do we hear these waves?
Our ears are our 'sound detectors'. The diagram shows the structure of an ear.
• The vibrations travel down the car canal.
• The vibrating air pushes on the eardrum so that it vibrates.
• The eardrum pushes the three small bones so that they vibrate.
• The smallest bone vibrates against the cochlea, which is a curled-up tube filled with liquid.
• The vibrations travel through the liquid, stimulating the nerve cells inside the cochlea. These send electrical signals along the nerve to the brain.

nerve three small bones eardrum cochlea ear canal — The structure of the human ear

1) The list below shows the parts of the car. List them in the correct order to show how the vibrations of a sound wave eventually reach the brain.
cochlea three small bones nerve ear canal eardrum brain

Hearing high and low
When you are young, you probably have good hearing.
You can hear very faint (quiet) sounds. You can hear very high-pitched sounds.
Older people gradually lose the ability to hear the faintest sounds and the highest sounds.
You can find out which are the highest and lowest notes you can hear using a signal generator and a loudspeaker.

The signal generator can make sounds with different frequencies

Your teacher will use the signal generator to make sounds with different frequencies.
What is the highest frequency you can hear? What is the lowest frequency?

Range of hearing

Most people can hear sounds with frequencies as low as $20 Hz$. Young people (aged under 20) can usually hear sounds of up to about $20000 Hz$.
As people get older, their hearing deteriorates.
By the time they are 50, they may not hear sounds above $15000 Hz$.
Sounds above $20000Hz$ are beyond the range of human hearing. Such sounds are known as ultrasound. Many animals can hear ultrasound.
Bats use ultrasound to find their way around. They emit high-pitched squeaks and listen to the reflected waves.

The bat listens for reflected ultrasound waves. In this way, it can tell how far it is from the wall

2) Which of the following frequencies would you expect a young person to be able to hear?
$500 Hz$, $6000 Hz$, $25000 Hz$, $15 Hz$, $15000 Hz$

Keep the volume down or you may damage your hearing

Noise annoys

There are many sounds we don't want to hear.
Unwanted sound is called noise.
Loud sounds can damage our cars. Listening to music through headphones can be harmful if you have the volume turned up too high.
Often there are laws to protect workers who work in noisy places. They should wear ear protectors so that they do not become deaf.

The chainsaw is noisy so the woodworker wears ear protectors

$A+I$: 3 Suggest some jobs where people have to work in a noisy environment.

Summary

• Our ears convert sound waves into nerve signals to the brain.
• Young people can usually hear sounds whose frequencies lie between 20 Hz and 20 000 Hz.
• Loud sounds can damage our hearing.