The Nature of Sound I

Question 1

what 3 things are related to mechanical vibrations

Answer 1

sound generation
propagation
perception of sound

Question 2

particle motion

Answer 2

motion of the particles interacts with the particles near them, and the energy is transferred to them spreading out to more remote areas

Question 3

what are sound waves

Answer 3

areas of pressure disturbances in the air

Question 4

what does the propagation of sound rely on

Answer 4

presence of a medium

Question 5

energy transfer takes time. what is this displacement

Answer 5

velocity

Question 6

what is speed of sound and what does it depend on?

Answer 6

speed at which sound waves travel
medium in which sound travels

Question 7

what type of wave is sound

Answer 7

mechanical
- transverse
- longitudinal

Question 8

what is a transverse wave?

Answer 8

the movement of the particles of the medium is perpendicular to the motion of the source

Question 9

what is a longitudinal wave?

Answer 9

the movement of the particles of the medium is in the same direction as the movement of the source

Question 10

what is wavelength (λ)?

Answer 10

distance between the particles of the medium that represent two successive peaks or valleys

Question 11

λ for transverse waves

Answer 11

distance from one peak to another or from one trough to another

Question 12

λ for longitudinal waves

Answer 12

distance from one point of compression to the next point of equal compression or one point of rarefaction to the next point of equal rarefaction

Question 13

wavelength equation

Answer 13

λ= velocity/frequency

Question 14

amplitude

Answer 14

maximum displacement of the particles of the medium from the average resting position

Question 15

amplitude in transverse waves

Answer 15

amplitude is reported in the direction that is perpendicular to wave source
- difference between the peak value and average value

Question 16

amplitude in longitudinal waves

Answer 16

amplitude is reported in the direction of wave source
- difference between the density of the compressions and the average value of the compressions

Question 17

frequency (f)

Answer 17

number of vibrations that occur in one second
- same for both wave types

Question 18

Period (T)

Answer 18

time taken for one complete vibration
- same for both wave types

Question 19

relationship between frequency and period

Answer 19

inverse
f=1/T
T=1/f

Question 20

wave velocity

Answer 20

velocity at which the wave propagates

v= frequency x wavelength

Question 21

effects of a medium

Answer 21

• usual experience is sound in air
• sound also can propagate in solids, fluids - sound CANNOT propagate in a vacuum (no media present)

Question 22

characteristics of a medium

Answer 22

• as sound propagates is that there are local regions of increased, equal or decreased regions of compression
• amount of compression/rarefaction and the return to equilibrium that is possible depends on the medium (elasticity property)

Question 23

elasticity

Answer 23

the ability of an object to return to equilibrium once it has been displaced from rest

Question 24

what does the speed of propagation depend on

Answer 24

physical properties of the medium

Question 25

speed of propagation in: pyrex, steel, water, air

Answer 25

Pyrex = 5640 m/sec
Steel = 4877 m/sec
Water = 1482 m/sec
Air = 343 m/sec

Question 26

how does temperature affect speed

Answer 26

basic properties of the medium are altered by changes in temperature

Question 27

density and speed for helium

Answer 27

Density (ρ) of air at normal temperature and pressure is 1.2kg/m3 in contrast to helium which has a density of 0.17 kg/m3

The speed of sound in helium is 927 m/s

Question 28

to get sound, we need a source that what?

Answer 28

vibrates

Question 29

young humans with normal hearing can hear vibrations that
range from 20 vibrations/sec (20 Hz) up to 20,000 vibrations/sec
(20,000 Hz). what does this assume?

Answer 29

• there is a medium for sound to propagate
• the amplitude of vibration is sufficient to allow hearing

Question 30

Tuning forks

Answer 30

• designed to create a sound when struck
• size of the tuning fork a specific frequency is created.
• used to tune musical instruments
• can be used in clinical assessments

Question 31

simple harmonic motion (SHM)

Answer 31

• described by a sine function
• sine wave

Question 32

sine wave

Answer 32

a waveform that has periodic oscillations in which the amplitude of displacement at each point is proportional to the sine of the phase angle of the displacement

Question 33

movement (pendulum)

Answer 33

• At 1, there is no movement
• The time it takes to go from 1 to 2 there is an acceleration
• The time it takes to go from 2 to 3 is less than the time to go from 1 to 2 so the acceleration is greater.
• At point 3 (center/middle) is the greatest acceleration
• From 3 to 4 the time it takes is less than the time from 4 to 5
• On the right side of 3 there is deceleration
• At 5 there is no movement briefly and changes direction
• The pattern in terms of acceleration and deceleration is now the same but in opposite directions
• SHM then is a consistent pattern of acceleration and
  deceleration
• The velocity is not constant

Question 34

Restoring force

Answer 34

force that operates to bring medium back to a state of equilibrium

pendulum- gravity
tuning fork- springiness

Question 35

Projected motion

Answer 35

image with constant distance between locations where each marking represents the output

Question 36

ultrasound

Answer 36

above limits of human frequency

Question 37

intrasound

Answer 37

below limits of human frequency

Question 38

supersonic

Answer 38

speed greater than speed of propagation

Question 39

sub-sonic

Answer 39

speed less than/below speed of propagation

Question 40

Mach 1

Answer 40

speed of propagation of sound in air