HCI Sounds Notes

Hwa Chong Institution Sec 4 Physics 1 Name: _________________________________________ Class: ___________ Date: ______________ Sec 4 Physics (IP / SSMT) Topic 16: Sound I can… By the end of this topic, you should be able to:  relate the loudness and intensity of a sound wave to the square of its amplitude  relate the pitch of a sound wave to its frequency  define ultrasound and give one use of ultrasound  know that a medium is required in order to transmit sound waves and the speed of sound is fastest in solids, then liquids and then air.  describe the production of sound by vibrating sources  describe the longitudinal nature of sound waves in terms of processes of compression and rarefaction  describe how the speed of sound can be determined using reflection of sound wave s  describe how the reflection of sound may produce an echo use it for measuring distances  *describe and explain the Doppler Effect and apply the concept in new situations Basics of Sound 16.1 SOUND PRODUCTION A sound wave is produced by a vibrating / oscillating source placed in an elastic medium. The medium can be any solid, liquid or gas. Usually, it is air. Questions: (a) What is the significance of the statement “Usually, it is air.”? (b) What is it meant by an elastic medium? Which of the following media are elastic; mud, steel, air, or water? (a) For human beings, the best medium for hearing sound is air. (b) Do not mistake elasticity for “ stretchiness”. It simply means the tendency of the particles in the medium to return to their original positions. In humans, our voice production process can be simplified as follows. The diaphragm pushes air from the lungs through the vocal folds in the larynx, the air pressure sets the elastic voca l folds into vibration. This process is called voicing. A periodic train of air pulses is thus produced which moves up the vocal pipe. Hence, the vibrating vocal folds act as the source of the sound waves produced. Image retrieved from http://www.singintune.org/voice-production.html

Hwa Chong Institution Sec 4 Physics 2 16.2 SOUND TRANSMISSION IN AIR Sound is a type of mechanical wave . This means that a sound wave can only pr opagate through a medium. Sound cannot travel through a vacuum. Sound wave in air is an example of a longitudinal wave. This means that energy in a sound wave travels in a direction parallel to the direction of vibration of the particles in the medium. Check you understanding Question: What are compressions and rarefactions? Undisturbed air molecules. If we zoom in more closely, we will observe the molecules to be in constant random motion, in agreement with the Kinetic Model of Matter. Arrangement of air molecules as a sound wave travels through the air. This is a snapshot in time. The picture on the left shows what it means by compressions and rarefactio