Unit 2 Waves & Sound Vocabulary and Formulas
Chapter 25
Vocabulary
Amplitude – The distance between the midpoint of a wave and the crest or trough of the wave.
Antinodes – The parts of the standing wave that is directly between two nodes, these will be the parts of the
standing wave that have the largest amplitude.
Blue Shift – This is the increase in light frequency due to the Doppler effect.
Bow wave – A V shape created by an object moving faster than the waves that it creates, formed by
overlapping circular waves coming out from the moving object.
Constructive interference –When two waves in superposition affect each other in a positive way, creating a
wave of greater magnitude.
Crest – The high point of a wave.
Destructive interference –When two waves in affect each other in a negative wave, creating a wave of smaller
magnitude.
Doppler Effect – The apparent change in frequency due to the motion of the source (or in some cases the
receiver).
Frequency – How often a vibration occurs (iteration per unit of time), most often measured in cycles per
second (Hertz).
Hertz – The measurement for frequency, one cycle per second.
In phase – This is when two waves are combining constructively.
Interference pattern – When two waves exist in the same space and affecting one another.
Longitudinal wave – A wave where the motion of the medium is in the same direction that the wave is moving.
Node – The node is the part of a standing wave that does not appear to move. It is actually the point where the
coming and going waves are canceling each other out.
Out of phase – This is when two waves are combining destructively.
Period –The time it takes to make one vibration. The amount of time for a pendulum to complete one back-andforth movement.
Red shift – A decrease in light frequency due to the Doppler effect.
Shock wave – The three dimensional shape created by overlapping spheres of sound waves, formed when an
object travels faster than the speed of sound.
Simple harmonic motion – The back and forth motion of a pendulum or the up and down motion of a spring.
Sine curve – This is the curve that represents a wave, showing its crests, troughs, wavelength, and amplitude.
Sonic boom – This sound is heard by observers on the ground when the sound wave of an object that has
surpassed the speed of sound passes them.
Standing wave – A standing wave has a wave going out and a wave coming back interact so that some parts of
the wave stay stationary and it appears not to be moving.
Superposition – The overlapping of waves in both space and time.
Transverse wave – This is a wave where the motion of the medium is perpendicular to the direction that the
wave is traveling.
Trough – The low point of a wave.
Vibration – A wiggle in time.
Wave – A wiggle in space and time (a wiggle in motion).
Wavelength – The distance between from the top of one crest to the top of the next, or from the bottom of one
trough to the bottom of the next.
Formulas
f =
1
T
T=
1
f
Wave Speed = wavelength x frequency
v = fλ
Chapter 26
Vocabulary
Beats – Periodic variations in loudness of sound created by interference between slightly different frequencies
Compression – A pulse of compressed air
Forced Vibration –Occurs when one vibrating object forces another object that it is touching to vibrate with it
Infrasonic – A sound below 20 hertz, which means that it is a pitch lower than a normal ear can hear
Natural Frequency – The frequency at which an object will naturally vibrate
Pitch – The description we use of our perception of the frequency of the sound waves that we hear
Rarefaction – An area of low air pressure, the opposite of compression
Resonance – Happens when forced vibration matches natural frequency, causes dramatic amplitude increase
Ultrasonic – A sound above 20,000 hertz, which means that it is a pitch higher than a normal ear can hear
Formulas
f Beats = f 2 − f1