Wednesday, June 13, 2012

How does Sound Travel?

            Whatever we hear with our ears is called sound. In scientific terms, sound is a kind of disturbance or vibration, which produces sensations in the ears. Like heat and light, sound is also a form of energy. Do you know how sound is produced and how it travels from one place to another?

Sound travels in the form of waves  

            A body produces sound when a part or the whole of it vibrates. When we strike a bell, the vibrations produce sound. If we touch a ringing bell with our hands, we can feel its vibrations. Similarly when a person speaks, the diaphragm in his throat vibrates producing sound. When these waves reach our ears we hear the sound.

            The frequencies of vibrations vary. Our ears are sensitive to sound frequencies ranging between 20 to 20,000 hertz. Human ears cannot perceive frequencies of less than 20 hertz and more than 20,000 hertz.

            Sound travels in the form of waves, which needs a medium to travel. They cannot travel in vacuum. This can be proved by a simple experiment.

            Take a glass bottle and connect it to a vacuum pump. Put a cork on its mouth. Suspend an electric bell inside this bottle. Connect the bell to a battery. It starts ringing and we can hear the sound clearly. Now start removing the air from the bottle with the help of the vacuum pump. As the amount of air in the bottle starts decreasing, the intensity of sound also starts decreasing. When all the air is sucked out of the bottle, we don not hear any sound. This experiment proves that a medium is always necessary for the propagation of sound waves.

            These facts lead to three conclusions. First, vibrations produce sound. Second, sound travels in the form of waves. And third, sound needs a material medium for its propagation. Sound can travel through gases, liquids and solids. It travels fastest in solids, followed by liquids and slowest in gases. It cannot travel in space because there is no material medium. It is for this reason that astronauts talk to each other with the help of radio sets in space.