IGCSE Physics 0625

3.4 Sound - Production of Sound by Vibrating Sources

This section describes how sound is produced by vibrating sources. Sound travels as waves, and these waves are created when something vibrates.

How Sound is Produced

Sound is produced by vibrations. When an object vibrates, it causes the air molecules around it to vibrate as well. These vibrations propagate outwards as longitudinal waves, which we perceive as sound.

Types of Vibrating Sources

Many different types of sources can produce sound. Some common examples include:

• String Instruments: The vibrating strings in instruments like guitars and violins are a classic example.
• Membranes: Drums and loudspeakers use vibrating membranes to create sound.
• Air Columns: Wind instruments like flutes and trumpets produce sound by the vibration of air within a tube.
• Human Voice: Our vocal cords vibrate to produce speech and singing.

Factors Affecting the Sound Produced

Several factors influence the pitch and loudness of the sound produced by a vibrating source.

Pitch

Pitch is our perception of how high or low a sound is. It is determined by the frequency of the vibration.

1. Frequency: The number of complete vibrations per second, measured in Hertz (Hz). Higher frequency means higher pitch.
2. Length of the vibrating element: For strings, a shorter string vibrates at a higher frequency (higher pitch). For air columns, shorter columns produce higher pitches.
3. Tension: For strings, increasing the tension increases the frequency (higher pitch).
4. Density and Width: For strings, increasing the density or width decreases the frequency (lower pitch).

Loudness

Loudness is our perception of how intense a sound is. It is related to the amplitude of the vibration.

1. Amplitude: The maximum displacement of the vibrating element from its resting position. Larger amplitude means louder sound.
2. Energy of the vibration: Greater energy input into the vibrating source results in a larger amplitude and louder sound.

Examples of Sound Production

Here are some specific examples of how different objects produce sound:

Object	How it vibrates	Frequency (approximate)	Pitch	Amplitude (approximate)	Loudness
Guitar String	Vibrates along its length	440 Hz (A4 note)	Medium	Small	Quiet
Drumhead	Vibrates across its surface	Variable, depends on size and tension	Low to Medium	Large	Loud
Flute Air Column	Air column vibrates at both ends	Variable, depends on length and opening	High	Small	Quiet
Human Vocal Cords	Vibrate when air passes over them	Variable, depends on vocal technique	Variable	Small	Variable

Figure: Suggested diagram: A simple diagram showing a vibrating string, a drumhead, and a flute, with arrows indicating the direction of vibration and labels for frequency, amplitude, pitch, and loudness.

Understanding how sound is produced is fundamental to understanding the properties of sound waves and how they are affected by different factors.