Chapter 25 Vocabulary
Vibration - Wiggle in time. Cannot exist in one instant, but needs time to move back and forth
Wave - Wiggle in space and time. Cannot exist in one place but must extend from one place to another
Vibrations produce waves
Simple Harmonic motion - Back and forth vibratory motion
Sine curve - A curve whose shape represents the crests and troughs of a wave
Crest - The high point on a wave as represented by a sine curve
Trough - The low point on a wave as represented by a sine curve
Midpoint of vibration - The home position, represented by a straight dashed line
Amplitude - Distance from the midpoint to the crest (or trough), measured in meters (or any other unit of
distance)
Wavelength - Distance from the top of one crest to the top of the next one, measured in meters (or any
other unit of distance)
Period - The time for one cycle, Units: seconds (or minutes, hrs, days, etc.)
Frequency - The number of cycles per time, generally measured in cycles per second, or hertz (Hz)
Hertz - Unit of frequency, One hertz = one vibration per second
Period-Frequency relationship - Frequency = 1/Period or Period = 1/Frequency
Wave Speed – Recall speed is distance divided by time, distance is the wavelength, period is the time - So
Wave speed = wavelength divided by period, Substitute for 1/frequency for period, and equation
becomes Wave speed = Wavelength times frequency
Transverse wave - A wave where the vibration (or disturbance) is at right angles to the direction the wave
is travelling
Longitudinal wave - A wave where the vibration (or disturbance) is in the same direction as the wave is
travelling
Interference pattern - A pattern formed by the overlapping of two or more waves that arrive in the same
region at the same time
Constructive interference - Adding of two or more waves when the wave crests overlap. Result is a wave
of increased amplitude
Destructive interference - Adding of two or more waves where crests of one wave overlap troughs of
another. Result is a wave of decreased amplitude
Out of phase - Term to describe two waves that are destructively interfering
In phase - Term to describe two waves that are constructively interfering
Standing wave - Wave in which part of the wave remain stationary and the wave appears not to be
traveling. Produced by interference between an incident and reflected wave
Nodes - The part of a standing wave that remains stationary
Antinodes - The points on a standing wave where maximum amplitude occurs
Doppler Effect - The change in perceived frequency of a wave to either the source of the wave moving,
the receiver of the wave moving, or both.
Blue Shift - Increase in the measured frequency of light (Doppler effect), occurs when receiver and source
of light move toward one another - Example) light we receive from Andromeda Galaxy is shifted to the
blue side of the color spectrum because the Milky Way and Andromeda are getting moving toward one
another
Red Shift - Decrease in the measured frequency of light (Doppler effect), occurs when receiver and source
of light move away from one another - Example) light we receive from most galaxies is shifted to the red
side of the color spectrum because most galaxies are moving away from the Milky Way
Bow wave - The V-shaped wave produced by an object moving on a liquid surface faster than the waves
it produces (picture the wake behind a boat that is traveling faster than the waves it makes)
Shock wave - A cone-shaped wave produced by an object traveling faster than the waves it produces
(Basically a 3-dimensional bow wave, Picture the “wake” behind an airplane traveling faster than the
waves it produces)
Sonic boom - The sharp crack heard by a listener when the shock wave produce by an airplane traveling
faster than the speed of sound arrives to their ears
Chapter 26 Vocabulary
Pitch - Term that refers to how high or low sound frequencies appear to be subjective impression of the
frequency of sound
Infrasonic - Sound waves with frequencies below 20 Hz
Ultrasonic - Sound waves with frequencies above 20,000 Hz *People cannot hear infrasonic and
ultrasonic sound waves
Compression - A disturbance in air or other matter where the pressure is increased - highest pressure
points on a sound wave
Rarefaction - A disturbance in air or other matter where the pressure is lowered - Low pressure points on
a sound wave
*Sound waves (and all longitudinal waves) travel as a series of compressions and rarefactions Compressions are the crests, Rarefactions are the troughs - The amplitude is represented by the amount
the material is compressed
Speed of Sound, temperature dependence - Sound travels faster in warm air than cold air, Speed of sound
in dry air at 0 degrees Celsius is 330 m/s, Speed of sound increases by 0.60 m/s for every degree of
temperature increase above 0 - So average speed of sound in room temperature air is about 340 m/s
Intensity of Sound (pg 393-394) Proportional to square of wave amplitude - is an objective (quantitative)
way to quantitatively measure sound waves (as in loudness)
Loudness (pg 394) – subjective (qualitative) way to describe sound waves. Different for different people
what seems “loud” to you may not seem “loud” to me
Decibel scale - The unit of sound intensity, 0 decibels is the human threshold of hearing an addition of 10
decibels means the sound intensity has been multiplied by 10
so add 10 db
Intensity multiplies by 10
add 20 db
Intensity multiplies by 100
(10 x 10)
add 30 db
Intensity multiplies by 1000 (10 x 10 x 10)
Forced Vibration - The vibration of an object that is made to vibrate by another vibrating object that is
nearby
Natural Frequency - A frequency at which an object will vibrate when struck. Some objects have more
than one natural frequency
Resonance - Occurs when the forced vibrations on an object match the object’s natural frequency.
Increase in wave amplitude results
Beats - Occurs when two tones of slightly different frequencies are sounded together. The sound seems to
fade in and out
Refraction – the bending of a wave because of a change in wave speed due to a change in medium.
Diffraction – the bending of a wave around a barrier.