We hear variety of sounds in our daily life. Thundering of clouds, chirping of birds, mewing of cats, rustling of leaves, music on the radio and television and noise of vehicles are some of the sounds that all of us are familiar with. Each sound has particular characteristics. Sound enables us to communicate with each other. Animals also communicate with other members of their species with the help of sound. Some sounds like music are pleasing to us and we like to hear them. But some sounds, for example noise in our surrounding is undesired. In this lesson we will study about the production and propagation of sound, human voice system, hearing, noise pollution and the ways to control it.
PRODUCTION OF SOUND
Sound is produced when an object is set to vibrate. Vibration means a kind of rapid to and fro motion of a particle. This to and fro motion of the particle causes the substances around it to vibrate. Thus sound spreads to the surroundings.
PROPAGATION OF SOUND
The speed of sound is the distance travelled by sound in one second. It is denoted by 'v'. It is represented by the expression, v = nλ, where 'n' is the frequency and 'X' is the wavelength.
The speed sound depends on the properties of the medium through which it travels, like temperature, pressure and humidity. In any medium, as the temperature increases the speed of sound also increases. For example, the speed of sound in air is 331 ms at 0°C and 344 ms1 at 22°C.
CHARACTERISTICS OF WAVE MOTION
1.In wave motion, only the energy is transferred not the particles2. The velocity of the wave motion is different from the velocity of the vibrating particles.
3.For the propagation of a mechanical wave, the medium must possess the properties of inertia elasticity, uniform density and minimum friction Among the particles
Types of mechanical wave
There Are Two Types Of Wave.
They are
1. Transverse wave
2. Longitudinal wave
Transverse wave
In a transverse wave the particles of the medium vibrate in a direction, which is perpendicular to the direction of propagation of the wave. E.g. Waves in strings, light waves, etc. Transverse waves are produced only in solids and liquids.
LONGITUDINAL WAVE
In a longitudinal wave the particles of the medium vibrate in a direction, which is parallel to the direction of propagation of the wave. E.g. Waves in springs, sound waves in a medium. Longitudinal waves are produced in solids, liquids and also in gases.
PROPERTIES OF SOUND
All sounds that we hear are not the same. There are some properties that differentiate one kind of sound from another. We will study about these properties now.
LOUDNESS
It is defined as the characteristic of a sound that enables us to distinguish a weak or feeble sound from a loud sound. The loudness of a sound depends on its amplitude. Higher the amplitude louder will be the sound and vice- versa. When a drum is softly beaten, a weak sound is produced. However, when it is beaten strongly, a loud sound is produced. The unit of loudness of sound is decibel (dB).
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