2 : SOUND
1 CHARACTERISTIC OF SOUND
2 INTENSITY OF SOUND
3 SOURCES OF SOUND : VIBRATING STRINGS AND AIR COLUMNS
4 NATURAL FREQUENCY AND RESONANCE
5 DOPPLER EFFECT
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AUDIBLE RANGE
ULTRASOUND
PITCH
INFRASOUND
LOUDNESS
THE SPEED OF SOUND
✏Molecules of the medium collide, allowing the wave to be
transmitted through it.
✏The speed of sound depends on elasticity of the medium.
✏The more elastic the medium, the faster the sound.
✏ Elasticity – the ability of a solid to return to its original shape after external forces have been exerted on it.
⭐Sound intensity is the sound power as it passes through a given area
⭐I = P / Area… (W/m2)
⭐Io = 1 x 10^-12 W/m2 (threshold of hearing) .
⭐-Intensity Level, β, is a comparison of two sound intensities (Ratio).
LOUDNESS
the intensity can be written in terms of the maximum pressure variation
Loudness - depends on the amplitude of sound wave
the amplitude of a wave indicates its energy. The greater the amplitude, the greater the energy.
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-The intensity of a sound is proportional to the square of the amplitude of the sound wave. (E ≈ I ≈ A2)
-Loudness is measured in decibels (dB)
-Loudness is measured in decibels (dB) Sound Intensity (E≈I≈A2)
6 INTERFERENCE OF SOUND WAVES ; BEATS
SOUND AND PITCH
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🔒Pitch - the frequency of a sound wave
🔒– The human ear is not equally sensitive to all frequencies
🔒-Most people cannot hear frequencies below 20Hz or above 16,000Hz
🔒-Most people are most sensitive to frequencies between 1,000 and 5,000 Hz
🔒-Battle of the Ages
🔒Musical Scale. Example “middle C” has a frequency of 262 Hz.
RESONANCE
NATURAL FREQUENCY
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🔥Natural frequency ✅ An object’s own set of frequencies__ ✅ _Depends primarily on elasticity and shape
-When the frequency of a forced vibration matches the an object’s natural frequency, a dramatic increase in amplitude occurs.
-Unfortunately, resonance is not always a good thing!
You hear the high pitch of the siren of the approaching ambulance, and notice that its pitch drops suddenly as the ambulance passes you. That is called the Doppler effect.
Refers to the change in frequency when there is relative motion between an observer of waves and the source of the waves
Doppler Shift - Change in sound frequency due to the relative motion of either the source or the detector.
-example: a passing car
When a vehicle with a siren passes you, a noticeable drop in the pitch of the sound of the siren will be observed as the vehicle passes. This is an example of the Doppler effect. An approaching source moves closer during period of the sound wave so the effective wavelength is shortened, giving a higher pitch since the velocity of the wave is unchanged. Similarly the pitch of a receding sound source will be lowered.
doppler wavelength change
doppler effect frequency
⭐When two or more waves superimpose each other with slightly different frequencies, then a sound of periodically varying amplitude at a point is observed. This phenomenon is known as beats. The number of amplitude maxima per second is called beat frequency. If we have two sources, then their difference in frequency gives the beat frequency.
⭐Number of beats per second
n = | f1 - f2| per second
7 DIFFRACTING AND SOUND
bending of sound around a barrier