During the school assembly, Kavitha noticed something interesting. When the tabla player struck the drum, she could see the surface of the tabla shaking slightly. When she placed her hand gently on the drum after it was struck, she felt it trembling under her fingers.
"Why is the drum shaking?" she wondered. Her music teacher explained, "That shaking is called vibration, and it is what makes sound!" Let us learn more about how sound is produced and how it reaches our ears.
How is Sound Produced?
Sound is produced when an object vibrates (moves back and forth very quickly). When you pluck a rubber band, it vibrates and makes a sound. When you beat a drum, the stretched skin vibrates and produces sound. When you speak, thin flaps inside your throat called vocal cords vibrate.
Place your fingers gently on your throat and hum. Can you feel the vibration? That is your vocal cords at work.
How Does Sound Travel?
Sound needs a medium (material) to travel through. It can travel through solids, liquids and gases, but it cannot travel through a vacuum (empty space).
Through air (gas): When your friend calls your name from across the playground, the sound travels through the air to reach your ears.
Through water (liquid): If you tap two stones together under water in a bucket, a person with their ear near the bucket can hear the sound. Fishermen in coastal villages of Kerala and Tamil Nadu know that fish can hear sounds in water.
Through solids: Press your ear against a wooden table and ask a friend to tap the other end gently. You will hear the sound clearly. Sound travels faster through solids than through air.
Loud and Soft Sounds
Some sounds are loud -- like a firecracker during Diwali, a bus horn on a busy road in Delhi, or thunder during the monsoon. Loud sounds are produced when objects vibrate with a large force.
Some sounds are soft -- like a whisper, the ticking of a clock, or the rustling of leaves. Soft sounds are produced when objects vibrate gently.
Pleasant and Unpleasant Sounds
Pleasant sounds are sounds we enjoy hearing. Examples: a song sung by your mother, the sound of a flute (bansuri), birds chirping in the morning, or the sound of rain falling on a tin roof.
Unpleasant sounds (noise) are sounds that disturb us or hurt our ears. Examples: honking of vehicles in traffic, loud crackers, construction work, or a mixer-grinder running at full speed.
Too much noise is called noise pollution. It can cause headaches, loss of hearing and difficulty in sleeping. Many cities in India, such as Mumbai and Kolkata, have rules about honking in certain areas. Hospitals and schools are declared "silence zones."
Musical Instruments of India
India has a rich tradition of music. Different instruments produce sound in different ways:
| Instrument | How Sound is Produced | Type |
|---|---|---|
| Tabla | Striking a stretched skin | Percussion |
| Sitar | Plucking stretched strings | String |
| Bansuri (flute) | Blowing air into a hollow bamboo tube | Wind |
| Mridangam | Striking a stretched skin on both sides | Percussion |
| Harmonium | Pumping air over metal reeds | Wind / Reed |
Protect Your Ears
Our ears are delicate. Very loud sounds can damage our hearing permanently. We should avoid bursting loud crackers close to our ears, listening to music at very high volume through earphones, and standing near loudspeakers for a long time.
Anil placed a few grains of rice on a drum (dholak). When he struck the drum, the rice grains jumped up and down. This happened because the skin of the drum was vibrating. The vibrating skin pushed the rice grains into the air.
Sunita and her brother made a toy telephone using two paper cups and a long string. When Sunita spoke into one cup, her brother could hear her voice through the other cup. The sound travelled along the string (a solid) from one cup to the other.
During the Pongal festival in Tamil Nadu, the sound of the nadaswaram (a wind instrument) playing at the temple was pleasant and melodious. But the sound of firecrackers bursting nearby was very loud and unpleasant, making little children cover their ears.
| Word | Meaning |
|---|---|
| Vibration | Rapid back-and-forth movement of an object |
| Medium | The material (solid, liquid or gas) through which sound travels |
| Vocal cords | Thin flaps in the throat that vibrate to produce voice |
| Noise pollution | Harmful or disturbing level of sound in the environment |
| Percussion | Instruments played by striking or beating |
Finished learning? Now test what you know!