Physics Form 5: Chapter 1 - Pitch of the Sound

Generally, there are three characteristics of sound:

• frequency affects pitch of the sound
• amplitude affects loudness of the sound
• wave form affects quality of the sound

1. Frequency - Pitch

The frequency of a wave is measured as the number of complete vibrations of particles of a medium per unit time. A commonly used unit for frequency is Hertz.

Pitch is an auditory sensation in which listener assigns musical tones to relative positions on a musical scale based on the frequency of sound. A high pitch sound corresponds to a high frequency sound wave and low pitch sound corresponds to a low frequency sound wave.



Changing Pitch:

A string vibrates with a particular fundamental frequency. However, it is possible, to produce pitches with different frequencies from the same string. The 4 properties of the string that affect its frequency are length, diameter, tension and density. The properties are as described:

• When the length of a string is changed, it will vibrate with a different frequency. Shorter strings have higher frequency and therefore higher pitch.
• Diameter is the thickness of the string. Thick strings with large diameters vibrate slower and have lower frequencies than thin ones.
• Tightening the string gives it a higher frequency while loosening it gives it a lower frequency. 
• The density of a string also affects its frequency. The denser the string, its molecules vibrate slower and its frequency will be lower. 

Name	Frequency Range (Hz)	Characteristics
Infrasonic	0 - 20	Very low frequencies of sound that the human ear can’t detect, but you mayfeel the rumbling of the waves through your body.
Sonic (AKA Audio)	20 - 20 000	Normal range for human ears, although not everyone (especially the elderly) will hear to the extremes of this range.
Ultrasonic	20 000 +	Beyond normal hearing for humans, although some animals (like dogs) hear part ways into this range. Also used in medicine (e.g. ultrasounds for pregnant women).