All that we hear with our ears is called sound. Scientifically, sound can be defined as disturbance which creates sensation of hearing in our ears.
Sound is also a type of energy, like heat and solar energy. Whenever vibrations occur in a body or its parts, sound is produced. Like in the case of bell, when the bell is struck, it vibrates which instead produces sound. By simply touching the ringing bell we can easily notice the vibrations in it. In case of living beings, whenever he speaks vibrations occur in the diaphragm of his throat. No sound can be produced without vibrations. Sound waves create from a vibrating body and it needs a medium to travel. When our ears receive these waves then we are able to hear sound. Our ears are capable of hearing sound of the frequency ranging from 20 and 20,000 hertz. We are unable to hear sound of the frequency lesser than or greater than the given range. A material medium is needed by the waves of the sound to travel from one place to another. Sound can not travel in vacuum. It can simply be proved by the following experiment.
Take a bottomless bottle of glass and connects it to the vacuum pump. Place a cork on its mouth. Hang an electric bell in the bottle and then connects it to a battery. The bell begins to ring and then we are able to hear the sound. With the help of vacuum pump evacuate all the air present in the bottle. With the decrease in the amount of air inside the bottle, the intensity of sound also starts decreasing. When the bottle is completely evacuated, we are unable to hear sound. This experiment proves that material medium is essential for the traveling of sound waves. By this experiment, we can drive three conclusions. Firstly, only vibrations can produce sound. Secondly, sound can travel only in form of waves. Thirdly, material medium is necessary for the traveling of sound.