Primary Science Week

What is sound?

What is sound : basic version

Sound is a wave of vibrating air. It moves as repeating areas of compression (bunches up particles) and rarefaction (spread out areas). When these vibration reach our ears, we interpret this as sound.

Sound is a type of energy. It is a type of pressure wave caused when something vibrates. A sound wave is also called a longitudinal wave.

When you clap your hands, air particles are forced together then apart again.

This creates ripples or sound waves that move outward from the source. As sound moves outward, it causes air to bunch up in some places then spread out. Sound pushes and pulls air back. If you look at it as a diagram, you can see repeating areas of compression (the bunched up areas) and rarefaction (the spread our areas)

???Did you know???

Sound travels faster and further in water and solids? This is because water is more dense than air. The molecules are closer together enabling sound to move faster. However, it takes more energy to generate the initial sound because of the density of water.

For more on oscilloscopes see the Science week activities page

Amplitude

Amplitude is the height of the waves (from the middle position). This determines how loud the sound is. The more pressure produced as the air particles are forced together when they vibrate will increase the volume or loudness.

We can measure how loud a sound is using a decibel (dB) meter.

Decibel is derived from the word deci meaning ten and bel. A bel is a unit of sound intensity named after Alexander Graham Bell. So decibel is one 10th of a bel.

The Hertz was named after German physicist Heinrich Rudolf Hertz.

Frequency and pitch

Frequency is the number of times the particles vibrate per second.

If we have sounds travelling at the same speed:

high frequency, or high-pitched sounds, have waves close together
low frequency, or low-pitched sounds, have waves further apart.

We can measure frequency in hertz (Hz). This is the number of pressure waves per second that would move past a fixed point.

How loud is too loud?

Prolonged exposure to sound over 85 dB will cause hearing loss over time.

How do we hear?

How do we hear? : basic version

When the vibration from sound waves reach our ears, it travels down the ear canal to the ear drum. The vibration is changed into an electrical impulse. Nerves send this to the brain and it is interpreted as sound.

Parts of the ear and their function

The external part of the outer ear is called the auricle or pinna. It helps gather sound vibrations and channel them into the ear or auditory canal to the ear drum or tympanic membrane. This membrane is a thin sheet of connective tissue. It forms the first part of the tympanic cavity which also contains air an three tiny bones (collectively called the ossicles). These bones are:

malleus or hammer
incus or anvil and
stapes or stirrups.

These are also parts of the middle ear. Sound waves cause the bones to vibrate with the stapes pushing a structure called the oval window in and out. The vibration continues to the inner ear. The cochlea is a fluid-filled, spiral shaped structure. Inside is the organ of Corti. Hairs within this structure translate the vibrations to electrical impulses. These impulses are carried by the cochlear nerve to the brain which interprets these electrical impulses as sound.

The auditory tube, also called the Eustachian tube, runs into the pharynx (a cavity behind the nose and mouth). It helps protect, aerate and drain the middle ear. Plus it helps maintain the air pressure in the middle ear.

The semicircular ducts and the vestibule (not shown) help us maintain our balance.