Ch.2 Sound

What do all waves carry from one location to another?

Energy

Sound is a _____ wave

Mechanical. It MUST travel through a medium where the molecules are alternately compressed and rarefied

Mechanical wave

A wave that needs a medium (material) to travel through

Vacuum

Empty space, has no particles so sound can’t travel through.

Sound waves are a series of

Compressions and Rarefaction (compress together and spread apart)

Compressions

Are areas of INCREASED pressure and density. Meaning it is squeezed together/tightly packed together.

Rarified

Are areas of DECREASED pressure and density. Meaning it is stretched apart.

Sound travels in a

straight line and are longitudinal waves

Sound waves summed up

A mechanical, longitudinal wave that travels in a straight-line carrying energy from one location to another through a series of compressions & rarefactions

Acoustic propagation properties

The effects of the medium upon the sound wave (what does the tissue do to the sound).

Biologic effects

The effects of the sound wave upon the biologic tissue through which it passes. (what does sound do to the tissue?)

Sound waves

also known as acoustic waves, are identified by oscillations in acoustic variables. Meaning, acoustic variables identify which waves are sound waves.

Three acoustic variables that are used to distinguish between sound waves and other types of waves.

Pressure, Density, Distance

If something OTHER than pressure, density, or distance rhythmically oscillates in a wave then

the wave is NOT a sound wave.

Pressure

Concentration of force in an area, force/area* Units: Pascals (Pa)*

Density

Concentration of mass in a volume. How much mass/how tightly its packed into a certain amount of space (volume) Units: kg/cm^3

Distance

Measure of particle in motion. How far a particle moves. Units: cm, feet, mile

How many acoustic parameters are used to describe the characteristics of a sound wave?

7: Period, Frequency, Amplitude, Power, Intensity, Wavelength, Speed

Acoustic parameters

describe the features of a particular sound wave.

Acoustic variables

Identify which waves are sound waves

In a transverse wave

Particles move in a direction that is perpendicular (right angle or 90 degrees) to the direction that the wave propagates. Wave moves left to right but the particles in the wave are moving up and down.

Propagates

travels or moves from one place to another.

In a longitudinal wave

The wave travels forward, AND the particles move back and forth in the same direction. Particles move in the same direction that the wave propagates.

In-phase

A pair of waves, peaks (maximum values) occur at the same time and at the same location. Similarly, the troughs of the waves (minimum values) occur at the same time and place.

Out-of-phase

their peaks occur at different times as do their troughs.

More than one sound beam may travel in a medium

True

A string being shaken up and down is an example of a longitudinal wave.

False

When two waves overlap at the same location and at the same time they

combine into a single new wave

Interference depends upon

the phase relationship of the pair of waves.

Constructive Interference

Occurs when a pair of in-phase waves results in the formation of a single wave of greater amplitude than either of its components. The resulting wave is greater than the original two waves.

Destructive Interference

Occurs when a pair of out-of-phase waves interfere and results in the formation of a single wave of lesser amplitude than at least one of its components.

Which types of waves will exhibit both constructive and destructive interference

Waves of different frequencies

What happens when two out-of-phase waves of equal amplitude interfere?

Complete destructive interference may occur.

In-phase waves are described as being 'in step'.

True

How many complete wave cycles happen in a certain amount of time

Frequency

Something about the medium that changes when sound passes through it

Acoustic variables