Properties of Sound

When we talk to someone, the sound is transmitted in the air. In this case, some molecules of air are pushed, and some molecules of air are farther apart. This motion of molecules transmits the sound.

- Molecules just vibrate to and from. Molecules do not move across the medium

- A slightly higher-pressure place is called compression.

- A slightly lower-pressure place is called rarefaction.

- Sound wave is longitudinal wave because the direction of molecular vibration and the direction of traveling sound wave are the same.

- Sound waves need any medium (solids, liquid and gas) when it is transmitted.

- Sound cannot travel through a vacuum.

- Sound travels faster in denser media. (It travels faster in liquids than in gases, and fastest in solids.)

Speed of sound

In the air, sound travels at a speed of about 340m/s (15 oC).

Pitch of sound

- The pitch of sound shows how high or low is. For example, girl’s voice is high pitched but boy’s voice is low pitched.

- The pitch of sound depends on the frequency. Low pitch is low frequency and high pitch is high frequency

- A man can listen sound waves with frequencies ranging from 20Hz to 20000Hz (20kHz). [Audible sound]

Loudness of sound

- The loudness of sound wave depends on the amplitude of the wave.

- A sound wave with larger amplitude contains more energy and therefore louder