Digital Sound & Music: Concepts, Applications, & Science, Chapter 2, last updated 6/25/2013
longitudinal wave. The coils that make up the slinky are moving back and forth horizontally, in
the same direction in which the wave propagates. The bouncing of a spring that is dangled
vertically amounts to the same thing a longitudinal wave.
Figure 2.7 Longitudinal wave
In contrast, in a transverse wave, the displacement of the medium is
perpendicular to the direction in which the wave propagates. A jump rope
shaken up and down is an example of a transverse wave. We call the quick
shake that you give to the jump rope an impulse like imparting a “bump” to
the rope that propagates to the opposite end. The rope moves up and down, but
the wave propagates from side to side, from one end of the rope to another.
(You could also use your slinky to create a transverse wave, flipping it up and
down rather than pushing and pulling it horizontally.)
Figure 2.8 Transverse wave
2.1.4 Resonance Resonance as Harmonic Frequencies
Have you ever heard someone use the expression, “That resonates with me”? A more informal
version of this might be “That rings my bell.” What they mean by these expressions is that an
object or event stirs something essential in their nature. This is a metaphoric use of the concept
of resonance.
Resonance is an object‟s tendency to vibrate or oscillate at a certain frequency that is
basic to its nature. These vibrations can be excited in the presence of a stimulating force like
the ringing of a bell or even in the presence of a frequency that sets it off like glass shattering
when just the right high-pitched note is sung. Musical instruments have natural resonant
frequencies. When they are plucked, blown into, or struck, they vibrate at these resonant
frequencies and resist others.
Resonance results from an object‟s shape, material, tension, and other physical
properties. An object with resonance for example, a musical instrument vibrates at natural
resonant frequencies consisting of a fundamental frequency and the related harmonic
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