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15 Cards in this Set
- Front
- Back
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Sound
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is a vibration or disturbance caused by something that has both mass and elasticity as it interacts with the medium around it. It is made up of compressions and rarefactions.
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Compressions
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Compressions occur when the presence of vibration causes the air molecules to become compressed. The pressure and density of these air molecules goes above atmospheric.
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Rarefactions
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Rarefactions occur in between compressions and the pressure and density of the air molecules is below atmospheric.
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Brownian motion
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the rapid, random motion of air molecules without sound impinging on them.
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longitudinal wave
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When the motion of the molecules and the wave propagation are going in the same direction (parallel) it is called a longitudinal wave. Sound is a longitudinal wave.
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transverse wave
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When the molecular motion and the direction of the wave propagation are perpendicular to one another it is called a transverse wave. Water waves are transverse waves.
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cycle
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A cycle is one complete compression and one complete rarefaction.
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period
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The duration of one cycle is called a period.
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acoustic properties
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The acoustic properties are the physical attributes of sound that can be measured in physical units.
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acoustic properties
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• Frequency
• Amplitude • Phase (Time) Aspects These attributes are independent on one another and thus can be changed independently of one another. |
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Frequency
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Frequency refers to the rate of vibration and is defined as the number of cycles per unit of time.
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Hertz
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Hz = # of cycles / second
Measurements of frequency. |
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wavelength and period
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All sound frequencies travel at the same rate but two acoustic parameters dependent on frequency are wavelength and period.
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Human hearing
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Human hearing ranges from 20Hz – 20,000Hz
*remember ultrasonic (very high and short frequencies used by bats) vs. subsonic (very low and long frequencies used by elephants) |
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C
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C = the speed of sound. It is affected by the medium. (For instance, sound travels faster in a solid where the particles are closer together than a gas where they are further apart. Similarly, the warmer the environment the faster the particles move.)
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