Question 1 How is sound produced?
Question 2 What should an object do to produce sound?
Question 3 How does a sound making object differ from one that is silent?
Question 4 Name the part which vibrates to produce sound in drums, sitar and flute?
Question 5 What brings the sound of a ringing telephone bell to our ears?
Question 6 How does propagation of sound take place?
Sound is that form of energy which makes us hear.
When an object moves backward and forward or to and fro rapidly, we say that the object vibrates or that the object is vibrating.
Sound is produced when an object vibrates. Whenever we hear a sound, then some object must be vibrating to produce that sound.
The vibrations of a sound producing object are quite large which we can see with our eyes. The vibration of the sound producing objects are so small that we cannot see them easily, we have to feel the vibrations of such an object by touching it gently with the fingers of our hand.
(1) Let us ring a bicycle bell and and touch it gently with our fingers. A ringing bicycle bell is shaking back and forth continuously. The bicycle bell is vibrating. If we hold the ringing bicycle bell tightly with our hands, it stop vibrating, and the sound also stops coming. Sound is produced by a vibrating bicycle bell.
(2) A body must vibrate to produce sound. The sound of a school bell is produced by the vibration of iron or brass plate when it is hit by a hammer.
(3) Stretch a rubber band and tie it tightly between two nails fixed on a table. In this position the rubber band is not vibrating and hence not producing any sound. Pluck the stretched rubber band in the middle with our finger. The rubber band starts vibrating and produce sound. Sound is produced when a stretched rubber band vibrates . If we hold the vibrating rubber bands tightly with our hand, the rubber band stops vibrating and the sound being produced by it also stops.
(4) Sitar is a musical instrument. It has many stretched strings are wires. If we pluck the string of a sitar in the middle, the Sitar makes a sound. If we now put our fingers gently on the Sitar strings, we can feel the strings vibrating. Sound is produced when sitar string vibrates.
(5) When we talk, we make sound. This sound is made by the vibration of two vocal cords present in our voice box fixed in the throat. Hold the fingers of our right hand gently on our throat and talk to one of our friends. When we are talking our fingers feels that something is moving on vibrating inside the throat. When we talk, air from the lungs passes up the windpipe. This air makes the vocal cords in our voice box to vibrate rapidly. And vibrating vocal cords produce the sound.
(6) Mosquitoes and bees make a buzzing sound by vibrating their Wings very very rapidly.
(7) If we blow across the mouth of an empty test tube, then a whistling sound is produced. This sound is produced by the vibration of air present in the test tube. The sound of a flute is produced by the vibrations of air column enclosed in the flute tube. The sound of a bursting balloon is produced by the vibration of air enclosed in the balloon.
(8) If we hit the stretched membrane of a tabla, the membrane starts vibrating and produces sound .If we put a few small pebbles on the membrane of this sound producing tabla, the pebbles will start jumping up and down showing that the tabla membrane is vibrating while producing sound. Sound is produced when the membrane of a tabla vibrates. Sound is produced when the stretched membrane of a drum vibrates.
(9) If we switch on a transistor radio, the thin cone of its speaker vibrates and produces sound.
(10) In a radio or television the thin cone of speaker vibrates backward and forward rapidly and produce sound.
Propagation of Sound
Sound is produced by the vibration of an object. When an object vibrates back and forth in air, then the molecules of air close to this object also starts vibrating back and forth with the same frequency. These vibrating air molecules pass on their motion to the next layer of air molecules due to which they also start vibrating back and forth. All the air molecules around the sound producing object start vibrating back and forth. When the vibrating air molecules fall on our ears, the ears feel these vibrations as sound. When an object vibrates then the air around it also starts vibrating in exactly the same way and carries sound to our ears through the vibration of its molecules. A sound wave travels from the sound producing object to our ears, through the air.