Sound

Sound

1. Sound Speed

   • Sound is a longitudinal wave because the vibrating molecules move in the same direction of the wave.
     • Speed of sound in a fluid
       • When the sound source is compressing a fluid, it’s important to take into consideration how difficult it is to compress the fluid (bulk modulus) and the inertia of the fluid (density).
         • Speed of sound in a metallic rod
           • When the sound source is compressing the molecules of a metallic rod, the elasticity (young modulus) and density of the metal are taken into consideration.
             • Speed of sound in an gas
               • When sound is propagating in a gas medium, then the adiabatic constant (ϒ) and the pressure (P) of the gas work act as the restoring force.

2. Sound characteristics

   • An open tube is when the ends of a pipe are open (like in a flute). As the air passes through the tube, the compressions and rarefactions of the sound waves form resonant frequencies
     • In a closed tube the wavelengths and frequencies are going to be different. There will be one node and one antinode at the beginning and the end of the tube.
       • Sound Intensity
         • Depending on the properties of sound, like frequency and intensity, is the kind of sound we will hear. The frequency of sound that a human can hear is a range from 20 Hz to 20 KHz.
           • The Bel scal
             • The intensity of sound is usually measured in bels (B).

3. Doppler Effect

   • This effect is the reason why you hear an approaching ambulance at a high pitch and once it passes you, you hear a low pitch.
     • refers to the apparent change in the frequency of a sound source when there is a relative movement of the source regarding to the listener.