Ch 7 - Waves and Sounds Flashcards
What type of oscillations to transverse waves have?
oscillations of wave particles perpendicular to the direction of wave propagation
What type of oscillations to longitudinal waves have?
oscillations of wave particles parallel to the direction of wave propagation (e.g. sound waves)
What is displacement in a wave?
how far a point is from the equilibrium position, expressed as a vector quantity
What is amplitude (A)?
the magnitude of a wave’s maximum displacement
What is a crest?
the maximum point of a wave (point of most positive displacement)
What is a trough?
the minimum point of a wave (point of most negative displacement)
What is the wavelength?
the distance between 2 crests or 2 troughs
What is the frequency?
the number of cycles a wave makes per second (Hz)
What is angular frequency (w)?
another way of expressing frequency and is expressed in radians per second
w = 2 x pi x frequency = (2 x pi)/T
What is a period?
the number of seconds it takes to complete a cycle (inverse of frequency) –> T = 1/f
What is interference?
describes the way in which waves interact in space to form a resultant wave
What is the difference between constructive, destructive, and partially constructive/destructive interference?
- constructive: occurs when waves are exactly in phase with each other (Aresultant = Ainterference1 + Ainterference2)
- destructive: occurs when waves are exactly out of phase with each other (Aresultant = Ainterference2 - Ainterference1) - exactly 180 degrees out of phase, Aresultant = 0
- partially: occurs when 2 waves are not quite perfectly in or out of phase with each other (Xresultant = Xinterference1 + Xinterference2)
What are traveling waves?
have continuously shifting points of maximum and minimum displacement
- have nodes and antinodes that move with wave propogation
How are standing waves produced?
by the constructive and destructive interference of 2 waves of the same frequency traveling in opposite directions in the same space
- have defined nodes and antinodes that do not move with wave propagation
What is the difference between antinodes and nodes?
- anti: points of maximum collision
- node: points where there is no collision
What is resonance?
the increase of amplitude that occurs when a periodic force is applied at the natural (resonant) frequency of an object
What is damping?
a decrease in amplitude caused by an applied or nonconservative force
How is sound produced?
by mechanical disturbance of a material that creates an oscillation of the molecules in the material
sound (v) = square root (bulk modulus (B) / density)
Where does sound propagate and when does is propagate fastest?
- through all forms of matter (but not a vacuum)
- fastest through solids, followed by liquids, and slowes through gases
How are density and speed of sound related within a medium?
as density increases, the speed of sound decreases
What is pitch?
related to frequency of sound
What is the Doppler effect?
a shift in the perceived frequency of a sound compared to the actual frequency of the emitted sound when the source of the sound and its detector are moving relative to one another
When is the apparent frequency higher than the emitted frequency?
when the source and detector are moving toward each other
When is the apparent frequency lower than the emitted frequency?
when the source and detector are moving away from each other
What determines the relationship between the apparent and emitted frequency?
the apparent frequency can be higher, lower, or equal to the emitted frequency when the 2 objects are moving in the same direction, depending on the relative speeds
When can shock waves be formed?
when the source is moving at or above the speed of sound
- shock waves are the buildup of wave fronts as the distance between those wave fronts decrease which occurs maximally when an object is travelling at exactly the same speed as the wave is travelling
- once an object moves faster than the speed of sound, some of the effects of the shock wave are mitigated because all of the wave fronts will trail behind the object, destructively interfering with them
What is intensity and what is it related to?
- I = P/A
- loudness or volume of sound is related to its intensity
- intensity is related to wave’s amplitude
When does intensity decrease?
over distance and some energy is lost to attenuation from (damping) from frictional forces
How does an open pipe support standing waves?
the length of the string or pipe is equal to some multiple of half wavelengths
How does a closed pipe support standing waves?
the length of the pipe is equal to some odd multiple of quarter wavelengths
How is sound used medically?
in ultrasound machines for both imaging (diagnostic) and treatment (therapeutic) purposes
What is wave speed (v)?
the rate at which a wave transmits the energy or matter it is carrying
- product of frequency and wavelength
What is the equilibrium position?
the point with 0 displacement in an oscillating system
How does applying a force at the natural frequency of a system change the system?
- the object will resonate because the force frequency equals the natural (resonant) frequency
- the amplitude of the oscillation will increase
What is the equation that relates wavelength of a standing wave and the length of the string that supports it?
wavelength = 2L/n
n = positive integer called harmonic which corresponds to the number of half wavelengths supported by the string
- frequency = nv/2L
How is harmonic determined when strings are attached to both ends of the pipe?
the number of antinodes present will tell you which harmonic it is
How is harmonic determined for open pipes?
the number of nodes present will tell you which harmonic it is
How is the harmonic determined for closed pipes?
- unlike strings and open pipes, one cannot simply count number of nodes or antinodes
- for closed pipes, have to actually count the number of quarter wavelengths contained in the pipe to determine harmonic
wavelength = 4L/n
How do ultrasound machines calculate distance?
based upon travel time of the reflected sound
What equation relates sound level to intensity?
Bf = Bi + 10log (If/Ii)
What does it mean for the difference between emitted and perceived frequencies to be 0?
implies that the source of the sound is not moving relative to the other object
