Physical Sound - Waves Flashcards
Identify the characteristics of sound waves and define how sound travels through a medium. (35 cards)
What is an intervening material between two points in space, which is made to vibrate by energy carried from one place to another?
A medium
Although waves are imaginary, they may be observed as what?
A pattern of change that spreads outwards, such as the ripple from a pebble dropped in water.
In a vibrating body, energy is held in a bistable state, alternately in what two forms?
Either force (potential energy) or movement (kinetic energy).
How do [imaginary] points of mass, trying to reach their equilibrium position after excitation, behave?
They move around their rest point, exchanging movement for force (and vice versa), which makes the vibrations of sound.
What is it called when the points of material are bunched up into a higher density than in the material at rest?
A compression
What is it called when the points of material are more spread out than in the material at rest?
A rarefaction
In wave propagation, what is simple harmonic motion?
Elasticity of the material flexes the points back towards their original position with a restoring force equal to the force carried by the wave. The restoring force causes the displaced parts to overshoot their original position and swing back-and-forth around their rest point, where the restoring force is inversely proportional to the displacement.
In wave propagation, how do longitudinal waves displace the medium?
In the same axis as the wave motion.
In wave propagation, how do transverse waves move in relation to the displacement of the medium?
In a direction perpendicular to the displacement of the medium.
Sound waves traveling through air move by what propagation?
Longitudinal propagation
Vibrating solids like a bell or plate may have either of what type of propagation wave?
Longitudinal or transverse waves
What is the amplitude of a wave?
The measured quantity at some point.
The amplitude of a wave has both negative and positive magnitudes relative to the rest point. For soundwaves, what do the positive and negative portions of a wave correspond to?
The positive part of the wave corresponds to a compression. The negative part of the wave corresponds to a rarefaction.
What is the difference between the most positive and most negative displacement of a wave called?
The range or peak to peak amplitude
The measurement between zero and the peak displacement is called what?
Regular amplitude
What is the formula to find the speed of sound through a given material?
c = square root of (K ÷ p)
What is particle velocity?
How fast a particle is moving at any instant.
Maximum particle velocity depends on what?
Frequency and amplitude
What is phase velocity?
The speed at which the waveform moves.
What is group velocity?
The speed at which energy travels.
For most acoustic situations, the phase and group velocity are what?
Equal
Group velocity is a constant that depends on the properties of what?
The medium
When is a medium considered dispersive?
When the group and phase velocity are not quite the same. We see a wave distort as it propagates.
What is the symbol for a wavelength?
Lambda
