Sound plays an important role in our lives. The ear being one of our sense organs gives us the ability to hear the world around us. Sound is vital to share information, creating art, interacting with people, regulating work schedules and many other countless aspects of life.
Let us understand:
Take a rubber band and put it around the longer side of the pencil box. Insert two pencils between the box and the stretched rubber. Now pluck the rubber band somewhere in the middle. What do you observe?
When a tightly stretched band is plucked, it vibrates and produces sound. When it stops vibrating, it does not produce sound. The to and fro, or back and forth motion of an object, is called vibration.
In humans, the sound is produced by the voice box or larynx. Put your fingers on the throat and find a hard bump that seems to move when you swallow. This part of the body is known as the voice box. Two vocal cords are stretched across the voice box in such a way that it leaves a narrow slit between them for the passage of air. When the lungs force air through the slit, the vocal cords vibrate, producing sound. Muscles attached to the vocal cords can make the cords tight or loose.
Why the voices of men, women, and children are different?
It is because the vocal cords in men are about 20 mm long. In women, these are about 5 mm shorter. Children have very short vocal cords.
We hear sound through our ears. The shape of the outer part of the ear is like a funnel. When sound enters our ears, it travels down a canal at the end of which is a thin tightly stretched membrane called the eardrum. Sound vibrations make the eardrum vibrate. The eardrum sends vibrations to the inner ear which sends the signal to the brain and that is how we hear.
Sound needs a medium for its propagation. It cannot travel in a vacuum. This is the reason why two astronauts cannot hear each other in space or the moon where there is no atmosphere. Sound can travel in solids, liquids and gases. Its speed is more in solid, less in liquids, and still less in gases. For example, the speed of sound in iron is nearly 5000 m/s, in water it is nearly 1500 m/s and in air, it is nearly 330 m/s. What this implies? It implies that the closer the particles lie the faster sound can travel.
Let's see how sound travels in a medium.
Imagine you listening to music through a speaker. How the sound from the speaker reaches your ear? A sound is a form of energy that needs material to travel. Sound travels as a wave or disturbance of air particles. When the music is playing the speaker is vibrating. When music is off, layers of air are stationary, but when the speaker is on, vibration disturbs these layers of air. The particles do not travel from the vibrating object to the ear. A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position. It then exerts a force on the adjacent particle. As a result of which the adjacent particle gets displaced from its position of rest. After displacing the adjacent particle the first particle comes back to its original position. This process continues in the medium till the sound reaches your ear. This is what happens during the propagation of sound in a medium, hence sound can be visualized as a wave.
When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called compression (C). This compression starts to move away from the vibrating object. When the vibrating object moves backward, it creates a region of low pressure called rarefaction (R). As the object moves back and forth rapidly, a series of compressions and rarefactions are created in the air. These make the sound wave that propagates through the medium. Compression is the region of high pressure and rarefaction is the region of low pressure. Pressure is related to the number of particles of a medium in a given volume. One complete to and fro motion forms one compression and one rarefaction which together constitute one wave. This wave in which the particles of the medium vibrate about their mean positions in the direction of propagation of sound is called a longitudinal wave.
Some terms related to wave:
1) Amplitude: The maximum displacement of the particle of a medium on either side of its mean position is called the amplitude of a wave. It is denoted by letter a and its S.I unit is meter.
2) Time period: The time taken by a particle of the medium to complete vibration is called the time period of the wave. It is denoted by the letter T and its S.I unit is second.
3) Frequency: The number of vibrations made by a particle of the medium in one second is called the frequency of the wave. It is denoted by the letter f and its S.I unit is second-1 or hertz(Hz).
In Time T, the number of waves = 1, therefore in 1 second number of waves or frequency is
\(f = \frac{1}{T}\)
4) Wavelength: The distance traveled by the wave in one time period of vibration of the particle of medium is called its wavelength and is denoted by symbol λ. Its S.I unit is meter. In a longitudinal wave, the distance between two consecutive compressions or two consecutive rarefactions is equal to one wavelength.
Sounds of frequencies less than about 20 vibrations per second(20 Hz) cannot be detected by the human ear. Such sounds are called inaudible. On the higher side, sounds of frequencies higher than about 20,000 vibrations per second (20 kHz) are also not audible to the human ear. Thus, for the human ear, the range of audible frequencies is roughly from 20 to 20,000 Hz. Some animals like dogs can hear sounds of frequencies higher than 20,000 Hz.
Let us create our own string telephone.
Material Required: 2 Paper Cup, piece of string around 2 foot, nail to make a hole in the paper cups
1. Use a nail to make a small hole in the bottom of each paper cup
2. Pull the string through the cup and tie a knot. Use a long piece of string to help the sound travel farther
3. One person can hold the phone up to their ear and the other person can talk into the other cup. Keep the string tight or the sound waves won’t travel correctly.
How does it work?
Sound waves are created when sounds make vibrations in the air. In this activity, your voice vibrates the air inside the cup, which is then transferred to the bottom of the cup. The bottom of the cup passes the sound waves to the string, and so on to the other cup.
