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Compare the sound of a baby with Hear the sound produced. Now bang the spoon on the tumbler and hear that of an adult. Is there any difference? Even if two sounds are equally loud, the sound produced again. Is the they differ in some way. Let us see how. sound louder when the tumbler is struck hard? Now suspend a small thermocol I wonder why my voice ball touching the rim of the tumbler is different from that of (Fig. 10.17). Vibrate the tumbler by my teacher. striking it. See how far the ball is displaced. The displacement of the The frequency determines the shrillness or pitch of a sound. If the ball is a measure of the amplitude of vibration of the tumbler. frequency of vibration is higher we say Now, strike the tumbler gently that the sound is shrill and has a higher and then a little harder. Compare pitch. If the frequency of vibration is lower, we say that the sound has a lower the amplitudes of vibrations of the tumbler in the two cases. In which pitch. For example, a drum vibrates with case is the amplitude larger? a low frequency. Therefore, it produces Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice, the loudness increases by a factor of 4. The loudness is expressed in a unit called decibel (dB). The following table gives some idea of the loudness of sound coming from various sources. Normal breathing 10 dB Soft whisper (at 5m) 30 dB Normal conversation 60 dB Busy traffic 70 dB Average factory 80 dB Above 80 dB the noise becomes physically painful. The loudness of sound depends on its amplitude. When the amplitude of vibration is large, the sound produced is loud. When the amplitude is small, Fig. 10.18 : Frequency determines the the sound produced is feeble. pitch of a sound SOUND 131 2024-25