# Ch 17 PS

## Terms

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A disturbance in matter that carries energy from one place to another.
Mechanical wave
The ability to do work
Energy
Mechanical waves require _____ to travel through
matter
Material through which a wave travels
medium
3 mediums are...
solids, liquids, and gasses
In a wave pool, what is the medium?
Water
Waves travel through a rope when you shake one end of it. What is the medium?
The rope
When is a mechanical wave created?
When a source of energy causes a vibration to travel through a medium.
Mechanical waves are classified...
by the way they move through a medium
3 types of mechanical waves
transverse, longitudinal, and surface
The highest point of a (transverse) wave above the rest position
crest
the lowest point below the rest position (transverse)
trough
A transverse wave carries energy in a direction ________ to the up and down motion of the medium.
perpendicular
an area where the particles in a medium are spaced close together (longitudinal)
compression
area where the particles in a medium are spread out (longitudinal)
rarefaction
a wave in which the vibration of the medium is parallel to the direction the wave travels
longitudinal
Longitudinal waves produced by earthquakes that can travel through earth- scientist use them to map earth's unseen interior.
P waves (aka primary waves)
Most familiar kind of surface wave
Ocean waves
A wave that travels along a surface seperating two media
surface wave
any motion that repeats at regular time intervals
periodic motion
A complete motion that returns to its starting pt (the time required for one cycle)
period
For an ocean wave, the period is the time between...
two successive crests
# of complete cycles in a given time
frequency
For a wave, the _____ is the number of wave cycles that pass a point in a given time
frequency
Frequency is measured in..
cycles per second, or hertz (Hz)
A wave's frequency equals..
the frequency of the vibrating source producing the wave
the dist. betwn a point on one wave and the same point on the next cycle of the wave
Wavelength
For a transverse wave, wavelength is
For a longitudinal wave, wavelength is
the distance btwn adjacent compressions or rarefactions.
Increasing freqency of a wave _____ its wavelength.
decreases
Speed =
wavelength x frequency
The speed of a wave can change if
it enters a new medium, or if variables such as pressure and temperature change
If you assume that waves are traveling at a constant speed, then..
wavelength is inversely proportional to frequency.
A wave with lower frequency has ____ wavelength.
longer
Max displacement of the medium from its rest position
Amplitude
The amplitude of a transverse wave is...
the distance from the rest position to a crest or a trough
It takes more energy to produce a wave with..
higher crests and deeper troughs
The more energy a wave has, the ______ its amplitude
greater
To measure the amplitude of a longitudinal wave...
use the max displacement of a point from its rest position (the more energy the wave has, the more the medium will be compressed or displaced)
occurs when a wave bounces off a surface that it cannot pass through
reflection
Reflection does not change the ___ or ___ of a wave but the wave can be flipped upside down.
speed, frequency
The reflected wave will be upside down compared to the original wave if the reflection occurs at...
a fixed boundary
the bending of a wave as it enters a new medium at an angle
Refraction
When a wave enters a medium at an angle, refraction occurs because..
one side of the wave moves more slowly than the other side
the bending of a wave as it moves around an obstacle or passes through a narrow opening.
Diffraction
When waves bend around an obstacle, _____ can also occur.
Diffraction
A wave diffracts more if its wavelength is...
large compared to the size of an opening or obstacle
When diffraction occurs, if the wavelength is small compared to the opening or obstacle, the wave..
bends very little
When diffraction occurs, the larger the wavelength is compared to the size to the opening or obstacle, the wave
diffracts more.
occurs when two or more waves overlap and combine together
interference
Two types of intereference
Constructive, destructive
The displacements of a wave combine to...
increase amplitude in constructive destructive interferenceintereference and decrease amplitude in destructive interference
Occurs when two or more waves combine to produce a wave with a larger displacement
Constructive interQference
Can reduce the amplitude of a wave
destructive interference
Occurs when two or more waves combine to produce a wave with a smaller displacement
Destructive interference
When a crest meets a crest, the amplitude...
increases
When a crest meets a trough, the amplitude...
is reduced
A wave that appears to stay in one place and does not seem to move through the medium
standing wave
Point on a standing wave that has no displacement from the rest position
Node
A point where a crest or trough occurs midway between two nodes
antinode
A standing wave forms only if half a wavelength or a multiple of half a wavelength...
fits exactly into the length of a vibrating cord
Longitudinal waves- compressions and rarefactions- that travel through a medium.
Sound waves
Many behaviors of sounds can be explained using.. (5)
speed, intensity, loudness, frequency, and pitch.
Waves travel fastest in ___
slower in ____
and slowest in ____
solids, liquids, gasses
(particles in a solid are closer together than particles in a liquid or gas)
The speed of sound depends on...
density and elasticity of the medium
the rate at which a wave's energy flows through a given area
Intensity
Sound intensity depends on both...
the wave's amplitude and the distance from the sound source
Sound intenisty levels are measured in...
decibels (dB) - a unit that compares the intensity of different sounds
The decibel scale is based on...
powers of ten
a physical response to the intensity of sound, modified by physical factors.
Loudness
As intensity increases, loudness _____
increases
the frequency of sound as you percieve it
pitch
sound at frequencies lower than most people can hear
Infrasound
sound at frequencies higher than most people can hear
Ultrasound
Ultrasound is used in...
sonar and ultrasound imaging
a technique for determining the distance to an object under water.
Sonar
S.O.N.A.R
Each ultrasound puplse
1/8000 of a second
A change in sound frequency caused by motion of the sound sorce, listener, or both.
Doppler effect
Doppler effect was discovered by...
Austrian scientist Christian Doppler. (1803-1853)
As a source of sound approaches, an observer hears a ____ frequency. As it moves away, a _____ frequency is heard.
higher, lower
3 system ear consists of
Outer ear, middle ear, and the inner ear
gathers and focuses sound into the middle ear
the outer ear
recieves and amplifies vibrations
middle ear
uses nerve endings to sense vibrations and send signals to the brain
inner ear
sound wave strikes eardrum, (a tightly stretched membrane between outer and middle) - & the eardrum vibrates at the same frequency as the sound waves striking it.
Outer ear
Contains hammer, anvil, & stirrup. When eardrum vibrates, the hammer vibrates at the same frequency. The hammer strikes the anvil, which moves the stirrup back and forth. The three bones act as a lever system to amplify the motion of the eardrum.
The middle ear
3 bones in middle ear
Hammer, anvil, & stirrup
Vibrations from the stirrup travel into the cochlea (a spiral shapes canal filled with fluid) The inside of the cochlea is lined w/ thousands of nerve cells with tiny hair-like projections. As the fluid in the cochlea vibrates, the projections sway back
Inner ear
Sound is recorded by...
converting sound waves into electronic signals that can be processed and stored.
Sound is reproduced by...
converting electronic signals back into sound wavesl
Most musical instruments vary their pitch by..
changing the frequency of standing waves
Musical instruments often use ___ to amplify sound
resonance
Response of a standing wave to another wave of the same frequency
Resonance
A wave entering a new medium at an angle will undergo _____ as one end of the wave changes speed.
Refraction
A cat can hear frequencies up to _______
65,000 Hertz
The ______ is a line drawn perpendicular to the barrier in a reflective wave
normal
Instead of crests and troughs, as in an ocean wave, a longitudinal wave has _____ and ______
compassion & rarefaction
An _____ _____ is a frequency higher than most people can hear
ultrasonic soundwave
In a transverse wave, ______ is measured from crest to crest or from trough to trough
Doppler Effect
The crest of a transverse wave is most similar to a(an) ______ in a longitudinal wave
compression
A _____ is the material through which a mechanical wave travels
medium
_______ measures the greatest displacement of a wave from the rest position
amplitude
A wave in a rope is a transverse wave, but a sound in a wave is a _____ wave
longitudinal
At the _____ of a standing wave, there is no displacement from the rest position.
node
In 1970, ___ ____ worked with noise cancellation technology
Barry Chaplain
The standard measure used to compare sound intensities is the ______
decibel
Earthquake waves are ____ as they pass through different layers of earth
refracted
The range of human hearing is _____ to _____ Hz
20 - 20,000 hertz
The _____ ____ is a change in sound frequency caused by motion of the sound source, motion of the listener, or both.
Doppler Effect
The part of the ear that is a funnel for sound waves is the _____ ear.
outer eat
____ ___ occurs when troughs of one waave meet crests of another wave.
interference
Once you find a frequency that produces a ____ ____, doubling or tripling the frequency will also produce it.
standing wave
Sounds greater than _____ dB can damage hearing.
90 - 120 decibels
A line drawn showing the direction a wave travels on a reflective wave is called a _____
ray
If two waves collide and form a temporary larger wave, the interference is _____
constructive
An _____ ____ is a frequency lower than most people can hear.
infrasonic soundwave
Waves in a rope are transverse waves because the medium's vibration is ____ to the direction in which the wave travels.
at right angles
____ ____ breoke the sound barrier by flying at a speed of 293 m/s at an altitude of 12,0000 m.
Chuck Yeager

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