Production and propagation of sound

Introduction to sound

Have you ever noticed how a generator vibrates when it is running, or how your throat feels when you shout? That shaking movement is what creates sound. In Physics, sound is a form of energy that we hear with our ears.

Simply put, sound is a message sent through the air by anything that shakes very fast.

Production of sound

Sound is produced whenever an object vibrates. When a bell is hit with a metal rod, it shakes back and forth very quickly. This vibration pushes the air around it, creating waves that travel to your ears. If you stop the vibration with your hand, the sound stops immediately.

Sources of sound in Nigeria include:

The vibration of strings in a guitar or 'goje'.

The vibration of air inside a whistle or a flute.

The vibration of a leather skin on a talking drum.

The vibration of the vocal cords in your throat when you speak.

Propagation of sound

Sound cannot travel through a vacuum or empty space where there is no air. It needs a 'carrier' to move from one place to another. This carrier is called a medium. Sound travels through solids (like a metal pipe), liquids (like water in a borehole), and gases (like the air around us).

This means propagation is just a fancy word for how sound travels or spreads.

How sound moves

Sound moves as a longitudinal wave. As the object vibrates, it creates regions where air molecules are pushed together and regions where they are spread apart. These regions move forward like a pulse along a 'slinky' spring.

1. Compression: This is a region where the air particles are pushed close together, resulting in high pressure.

2. Rarefaction: This is a region where the air particles are spread far apart, resulting in low pressure.

A single cycle of sound consists of one compression and one rarefaction.

Transmission through different media

Sound travels fastest in solids because the atoms are packed very tightly. It travels slower in liquids and slowest in gases like air. This is why you can hear a train coming from far away if you put your ear on the rail track before you hear it through the air.

Example calculation

A sound wave has a frequency of 500 Hz and a wavelength of 0.68 m. Calculate the speed of the sound wave in air.

1. Write down the formula: Speed (v) = frequency (f) x wavelength (L).

2. Insert the numbers: v = 500 x 0.68.

3. Calculate the result: v = 340 m s^-1.