The Nature of Waves

Discussion

definition

examples, examples, examples.

basic properties

types 1

classed by medium

mechanical
electromagnetic
gravitational
matter waves

types 2

classed by orientation of change

transverse
- synonyms
  - shear
- examples:
  - light and all electromagnetic waves
  - musical instruments
    - chordophones - vibrating strings (violin, guitar, piano)
    - membranophones - vibrating membranes (drums, vocal chords, kazoo?)
    - idiophones - vibrating solid object (bells, glockenspiel, xylophone, mbira)
  - seismic
    - secondary (S) shear
  - animal locomotion
    - vertebrates (snakes, fish)
- parts
  - crest: the high, the greatest positive displacement
  - trough: the low part, the lowest negative displacement
longitudinal,
- synonyms
  - pressure, compression, density
- examples
  - sound
  - musical instruments
    - aerophones - vibrating columns of air (horns, whistles, organ pipes )
  - seismic
    - primary (P) pressure
  - animal locomotion
    - invertebrates (worms)
  - traffic jams
  - density waves in spiral galaxies generate the arms
- parts
  - compressions (a.k.a. condensation): the pressed part, the greatest positive pressure change, a region where the medium is under compression
  - rarefactions (a.k.a. dilations): the stretched part, the lowest negative pressure change, a region where the medium is under tension
[magnify]
surface, interface, complex
- ocean
  
  [magnify]
- seismic waves come in two basic families
  - body waves, which have already been discussed
    - Primary (longitudinal, compression, Pressure)
    - Secondary (transverse, Shear), can't propagate through liquids
  - surface waves, which are what this discussion is a part of
    - Love, (Lateral shear)
    - Rayleigh, (elliptical, plate waves, ground Roll), something like ocean waves, but elliptical instead of circular
torsional
- ribbons, plates, bars
- bridges, skyscrapers
unclassifiable
- animals
  - arthropod locomotion (centipedes, millipedes, caterpillars)
  - peristalsis
  - nerve impulses
  - heart contractions
- dominoes

types 3

classified by duration

episodic
periodic

speed, amplitude, wavelength, period, phase, frequency

seismic energy propagates through the earth within the 50 Hz to 0.001 Hz range! The expression "long period" (greater than 10 seconds) and "short period" (less than 1 second or greater than 1 Hz)

types 4

classified by appearance

traveling
standing

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