a quiet room light traff ic a whisper a large off ice in working hours waves on the beach a scream a rock concert a vacuum cleaner a car horn a plane taking off A tuning fork is an object that helps us to perform in tune — that is, perform musical notes at the right pitch. When we hit it , it vibrates 440 times per second (440 Hz). This is the f requency of the note La or A. How sound is measured A lthough we can' t see sound waves travelling through air, they are a physical phenomenon that can be measured and analysed with special dev ices . The duration of a sound depends on how much time a sound wave lasts ( longer or shor ter waves) and we measure it in seconds. The pitch of a sound depends on the frequency of the v ibration of the sound waves (number of v ibrations per second ). We measure it in her tz (Hz). The intensit y of a sound depends on the amplitude of its waves ( larger or smaller waves). We measure this in decibels (dB). 21. FIND OUT how many decibels these sounds approximately have. ➔ The threshold of hearing is the minimum sound level that we need to hear a sound. Humans can hear sounds louder than 0 dB. ➔ The threshold of pain is the sound level f rom which a sound becomes unbearable and painful . For human beings this threshold is 120 dB. 17
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