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### 15 Cards in this Set

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 Sound 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. Compressions 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. Rarefactions Rarefactions occur in between compressions and the pressure and density of the air molecules is below atmospheric. Brownian motion the rapid, random motion of air molecules without sound impinging on them. longitudinal wave 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. transverse wave 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. cycle A cycle is one complete compression and one complete rarefaction. period The duration of one cycle is called a period. acoustic properties The acoustic properties are the physical attributes of sound that can be measured in physical units. acoustic properties • Frequency • Amplitude • Phase (Time) Aspects These attributes are independent on one another and thus can be changed independently of one another. Frequency Frequency refers to the rate of vibration and is defined as the number of cycles per unit of time. Hertz Hz = # of cycles / second Measurements of frequency. wavelength and period All sound frequencies travel at the same rate but two acoustic parameters dependent on frequency are wavelength and period. Human hearing 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) C 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.)