Sound Wave

In general, all sounds originate from vibration of something. The human vocal sound comes
from the vibration of the vocal cords. The rapid vibration of the cord causes a disturbance in the
air that travels as a sound. Depending on the thickness of the vocal cords, sounds of different
pitches are produced. Thick cords produce sounds of low pitch and think cords produce higher
pitch. Women and small children have cords that are short and thin as such they have high
pitched voice.

Sound is a longitudinal wave that travel through the air or another medium and can be heard
when it reaches a person’s or animal’s ear. Sound needs a medium to travel and the conditions
such as the density, temperature and so on affect the speed of the sound. For example, sound
travels faster in a solid medium than in the air. It is because in solid medium the atoms are
closely packed and the energy that travels as sound propagates much faster. Similarly, sound
travels faster in hot air than in a cold air. Since moon does not have atmosphere on it one may
shout as much as one wants on the moon but no sound will ever be produced.

Human ears can hear sounds of frequency ranging from 20 hz to 20000 hz. Those are audible
sounds. Sounds having frequencies that are beyond that range are called inaudible sounds.
They are inaudible to human ears. However, there are animals who could hear sounds of higher
or lower frequencies. For instance, bats can hear sounds with frequency greater than 20000 hz.