Chapter 10: Sound
Sound is Produced by a Vibrating Body
Sound is a form of energy that we can hear. It is produced when an object vibrates. A vibration is a rapid to and fro or back and forth motion of an object. In humans, the sound is produced by the voice box or the larynx, which contains two vocal cords that vibrate when air passes through them.
Sound Needs a Medium for Propagation
Sound needs a material medium like solid, liquid, or gas to travel. The vibrating object causes the particles of the medium around it to vibrate. This disturbance travels through the medium from particle to particle. Sound cannot travel through a vacuum, which is a space with no matter.
How We Hear Sound: The Human Ear
We hear sound through our ears. The shape of the outer part of the ear is like a funnel. When sound enters it, it travels down a canal to a thin stretched membrane called the eardrum. The eardrum vibrates, and these vibrations are sent to the inner ear. From there, the signal goes to the brain, which interprets it as sound.
Characteristics of Sound
Vibratory motion is also known as oscillatory motion. The following terms describe the characteristics of a sound.
- Amplitude: The maximum displacement or distance moved by a point on a vibrating body or wave measured from its equilibrium position. The loudness of a sound depends on its amplitude. A larger amplitude results in a louder sound. Loudness is expressed in a unit called decibel (dB).
- Frequency: The number of oscillations per second. The pitch (shrillness or flatness) of a sound is determined by its frequency. A higher frequency results in a higher pitch (a more shrill sound). Frequency is expressed in hertz (Hz).
- Time Period: The time taken for one complete oscillation.
Audible and Inaudible Sounds
The human ear can detect sounds within a specific range of frequencies.
- Audible Sound: The range of frequencies that a human can hear, which is approximately from 20 Hz to 20,000 Hz.
- Inaudible Sound: Sounds with frequencies below 20 Hz (infrasound) or above 20,000 Hz (ultrasound) cannot be heard by humans. Some animals, like dogs, can hear ultrasound.
Noise and Music
Sound that is unpleasant to the ear is called noise. Sound which is pleasing to the ear is called music. Music is produced by regular, periodic vibrations, whereas noise is produced by irregular vibrations.
Noise Pollution
The presence of excessive or unwanted sounds in the environment is called noise pollution. Major sources include sounds of vehicles, explosions, machines, and loudspeakers.
Exposure to loud noise over a long period can lead to health problems like lack of sleep, hypertension (high blood pressure), anxiety, and even temporary or permanent hearing impairment.
Measures to Limit Noise Pollution: We can reduce noise pollution by installing silencing devices in engines, planting more trees (as they absorb sound), avoiding the use of vehicle horns unnecessarily, and running industries away from residential areas.
Frequently Asked Questions (FAQ)
What is the difference between loudness and pitch?
Loudness is determined by the amplitude of the sound wave; a higher amplitude means a louder sound. Pitch is determined by the frequency; a higher frequency means a higher-pitched (more shrill) sound.
Why can't sound travel in space?
Sound is a mechanical wave, which means it requires a medium (like air, water, or solids) to travel by vibrating particles. Space is a vacuum, meaning it has virtually no particles to carry the vibrations.
What is the unit of frequency?
The unit of frequency is Hertz (Hz). One Hertz is equal to one vibration or oscillation per second.
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