properties of Sound Waves• Reflection• Refraction• Diffraction• Interference
Reflection* The return of sound waves from surfaces onwhich they are incident. * Reflection of sound waves off of surfaces canlead to a phenomena called ECHOES*When sound reflects off a special curved surfacecalled a parabola, it will bounce out in a straight lineno matter where it originally hits.
• Echoes are the sound of your own voice reflecting back to your ears.• A sound wave will continue to bounce around a room, or reverberate, until it has lost all its energy.• A wave has some of its energy absorbed by the objects it hits.
• Smooth walls have a tendency to direct sound waves in a specific direction.• Rough walls tend to diffuse sound, reflecting it in a variety of directions.
RefractionRefraction is the bending of waveswhen they enter a medium wheretheir speed is different.
Refraction of sound waves is mostevident in situations in which the soundwave passes through a medium withgradually varying properties.
• Sound propagates in all directions from a point source. Normally, only that which is initially directed toward the listener can be heard, but refraction can bend sound downward. Normally, only the direct sound is received. But refraction can add some additional sound, effectively amplifying the sound. Natural amplifiers can occur over cool lakes.
Diffraction• The BENDING of waves around small obstacles – The sound with longer wavelength compared to the obstacle will sound loudest – The amount of diffraction that occurs depends on both the size of the obstacle and the wavelength of the sound. The SPREADING OUT of waves beyond small openings - the smaller the gap size then Maximum diffraction occurs and the sounds spreads out greatly
Spreading Out of Waves• Bigger Gap size Smaller Gap size
• Is the phenomenon that occurs when two waves meet while traveling along the same medium.• The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium.
Constructive Interferene• Occurs at any location along the medium where the two interfering waves have a displacement in the same direction.• Both waves have an upward displacement; consequently, the medium has an upward displacement that is greater than the displacement of the two interfering pulses.• Observed at any location where the two interfering waves are displaced upward. But it is also observed when both interfering waves are displaced downward.
Principle of superposition• When two waves interfere, the resulting displacement of the medium at any location is the algebraic sum of the displacements of the individual waves at that same location.
• when one object vibrating at the same natural frequency of a second object forces that second object into vibrational motion.• The word resonance comes from Latin and means to "resound" - to sound out together with a loud sound.• It is a common cause of sound production in musical instruments• .
• *Another example are the woodwind instruments When air is blown through the reed, the reed vibrates producing turbulence with a range of vibrational frequencies , the result of resonance is a big vibration, the reed and air column sound out together to produce a loud sound.• *Brass instruments involve the blowing of air into a mouthpiece. The vibrations of the lips against the mouthpiece produce a range of frequencies. One of the frequencies in the range of frequencies matches one of the natural frequencies of the air column inside of the brass instrument. This forces the air inside of the column into resonance vibrations. The result of resonance is always a big vibration - that is, a loud sound.
• It is an effect produced by a moving source of sound wave• There is an upward shift in the frequency for the observer being approached by the source• There is a downward shift for the observer from whom the source is receding
• The Man• - Hears the sound of the shorter wavelengths• - Higher frequency• - Higher pitch• The Woman• - Hears the sound of the longer wavelengths• - Lower frequency• - Lower pitch