Sound

Sound

1. Produced when objects vibrate in medium

   • Energy transferred from one point to another

2. Longitudinal Wave

3. Motion of particles

   • Compression
     • Regions with air pressure > surrounding air pressure
       • Sound Graphs
         • Pressure-Distance Graph
         • Displacement-Distance/Time Graph
           • On the way down, 0 displacement = compression
             • On the way up, 0 displacement = rarefaction
         • to check the next motion of specific particle, look at the particle before it (considering direction of motion).
   • Rarefaction
     • Regions with air pressure < surrounding air pressure

4. Transmission

   • Human ear sound range: 20Hz to 20kHz
     • Ultrasound is > 20k hz, people cannot hear ultrasound
       • uses of ultrasound
         • Prenatal scanning, scan foetus
   • cannot be transmitted through vacuum
   • Different medium, different speeds.
     • Solid fastest, air slowest
       • in solids, atoms more closely packed
   • in deeper water, less friction, travel faster, shorter wavelength

5. Reverberation

   • Prolonged sound due to merging echoes (many reflections in a room)
   • Echo usages: measure distance of seabed (sonar)
   • To reduce echo, use rugs as they scatter sound wave and reduce reflected sound

6. Characteristics

   • Loudness
     • affected by amplitude of wave (larger amplitude, louder sound)
   • Pitch
     • affected by wavelength/frequency of sound wave (shorter wavelength/higher frequency, higher pitch)
       • v = f x 入

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