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the transfer of energy through a material
without the material itself moving along with the energy |
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Mechanical waves - a physical disturbance within
an elastic medium |
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Hooke’s law - within the elastic limit all
materials will exert restoring forces in response to an applied force |
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Electromagnetic waves - electrical and magnetic
disturbances which do not require any medium to transmit the energy |
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transverse wave |
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moves objects perpendicular to the direction of
wave motion |
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longitudinal waves |
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moves objects parallel to the direction of wave
motion |
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also called compressional waves |
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sound is a longitudinal wave |
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Superposition |
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constructive interference |
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destructive interference |
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Resonance |
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the forced vibration of an object by a wave
having the same natural frequency |
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Other terms |
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beats |
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nodes / antinodes |
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Periodic Wave Motion (Continuous wave)
speed = frequency x
wavelength |
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frequency |
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the number of waves per unit of time |
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1 Hz = 1
wave per second |
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wavelength |
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the
distance between two points on a wave which are in phase |
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The period (T)is the reciprocal of the frequency |
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The speed of sound is not dependent on f or l |
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it depends on the medium
it is travelling through |
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also dependent on temperature |
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vsound = 331 m/s at 0°C (inc. 0.6 m/s / °C) |
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Intensity is the power per unit of area. |
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Measured in watts / m2 |
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Hearing threshold Io= 10-12 W/m2 |
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The decibel scale is a comparison to a standard |
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Intensity range |
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hearing 0 d b = 10-12
W/m2 |
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normal conversation 65 d b |
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damage 160 d b = 104
W/m2 |
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Physical property Sensory effect |
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intensity
loudness |
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frequency
pitch |
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waveform quality |
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Frequency |
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infrasonic
- f < 20 Hz |
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audible sound -20 Hz < f < 20,000 Hz |
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ultrasonic - f > 20,000 Hz |
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Ultrasonic - above the hearing range |
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Useful in diagnostics and in therapy |
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Diagnostics |
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f = 1 to 20 MHz |
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I = 10-2 W/m2 |
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Smallest observable detail Ë 1 l |
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Useful depth Ë 200 l |
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Therapy |
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Convert sound energy to thermal energy |
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Caution with intensity |
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Notes