Production of Sound | Sound

SOUND Everyday we hear sounds from various sources like humans, birds, bells, machines, vehicles, televisions, radios etc. Sound is a form of energy which produces a sensation of hearing in our ears. There are also other forms of energy like mechanical energy, heat energy, light energy etc. We have talked about mechanical energy in the previous chapters. You have been taught about conservation of energy, which states that we can neither create nor destroy energy. We change it from one form to another. When you clap, a sound is produced. Can you produce sound without utilising your energy? Which form of energy did you use to produce sound? In this chapter we are going to learn how sound is produced and how it is transmitted through a medium and received by our ear. Thread Table tennis ball can just Vibrating tuning fork Fig. 12.1: Vibrating tuning fork just touching the suspended table tennis ball. Activity 12.2 Fill water in a beaker or a glass up to the brim. Gently touch the water surface with one of the prongs of the vibrating tuning fork, as shown in Fig. 12.2. Next dip the prongs of the vibrating tuning fork in water, as shown in Fig. 12.3. 12.1 Production of Sound Activity 12.1 Take a tuning fork and set it vibrating by striking its prong on a rubber pad. Bring it near your ear. Do Observe what happens in both the hear cases. you Touch one of the prongs of the vibrating tuning fork with your finger and share your experience with your friends. Now, suspend a table tennis ball or a small plastic ball by a thread from a support [Take a big needle and a thread, put a knot at one end of the thread, and then with the help of the needle pass the thread through the ball]. Touch the ball gently with the prong fork (Fig. 12.1). Observe what happens and discuss with your friends. any sound? Discuss with your friends why this happens. Vibrating tuning fork Glass Water of vibrating tuning a Fig. 12.2: One of the prongs of the vibrating tuning fork touching the water surface. plucked vibrates and produces sound. If you have never done this, then do it and observe the vibration of the stretched rubber band. -Vibrating tuning fork Activity 12.3 Glass Make a list of different types of musical instruments and discuss with your friends which part of the instrument vibrates to produce sound. Water 12.2 Propagation of Sound Fig. 12.3: Both the prongs of the vibrating tuning fork dipped in water. From the above activities what do you conclude? Can you produce sound without a vibrating object? In the above activities we have produced sound by striking the tuning fork. We can also produce sound by plucking, scratching, rubbing, blowing or shaking different objects. As per the above activities what do we do to the objects? We set the objects vibrating and produce sound. Vibration means a kind of rapid to and fro motion of an object. The sound of the human voice is produced due to vibrations in the vocal cords. When a bird Sound is produced by vibrating objects. The matter or substance through which sound is transmitted is called a medium. It can be solid, liquid or gas. Sound moves through a medium from the point of generation to the listener. When an object vibrates, it sets the particles of the medium around it vibrating. The particles do not travel all the way 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. The disturbance created by a source of sound in flaps its wings, do you hear any sound? Think how the buzzing sound accompanying a bee is produced. A stretched rubber band when Can sound make a light spot dance? Take a tin can. Remove both ends to make it a hollow cylinder. Take a balloon and stretch it over the can, then wrap a rubber band around the balloon. Take a small piece of mirror. Use a drop of glue to stick the piece of mirror to the balloon. Allow the light through a slit to fall on the mirror. After reflection the light spot is seen on the wall, as shown in Fig. 12.4. Talk or shout directly into the open end of the can and observe the dancing light spot on the wall. Discuss with your friends what makes the light spot dance. Mirror Piece Source of light Stretched balloon Slit Food can Wall Fig. 12.4: A beam of light from a light source is made to fall on a mirror. The reflected light is falling on the wall.