WAVES: sound and seismic

1
WAVES sound and seismic

• Chapters 25.1-25.8 26

2
Simple Harmonic Motion

• The equal or balanced back and forth or side to
  side motion of a particle that is caused to
  vibrate by a disturbance.
• Similar to a pendulums motion.
• http//www.physics.uoguelph.ca/tutorials/shm/Q.shm
  .html

3
WHAT IS A WAVE?

• A repeating disturbance that causes vibrations
  and transmits energy through matter or space.

4
WHAT IS THE PURPOSE OF A WAVE?

• To transmit energy from one place to another.

5
WHAT HAPPENS TO ENERGY AS THE WAVE TRAVELS?

• Energy is transferred from one particle to the
  next.
• The motion of particles in a medium is like the
  motion of masses on a spring.
• Energy of the wave spreads away from the
  disturbance or vibration (see white board)

6
IS MATTER TRANSMITTED WITH THE WAVE?

• No, only energy is transmitted.
• The particles in the matter vibrate as the wave
  passes, but do not travel with the wave.
• http//www.infoline.ru/g23/5495/Physics/English/wa
  ves.htm
• http//members.aol.com/nicholashl/waves/movingwave
  s.html

7
ARE THERE DIFFERENT TYPES OF WAVES?

• Mechanical Waves Non-mechanical waves

microwaves
Sound waves
8
Mechanical Waves

• Waves that can only travel through matter
• Examples sound, water and seismic waves
• In general, mechanical waves travel fastest
  through solids, then slower through liquids and
  slowest through gases
• Can be transverse or longitudinal (or
  compressional)

9
Electromagnetic Waves

• Waves that can travel through matter or space (a
  vacuum)
• Example electromagnetic radiation (waves) or
  light
• In general, non-mechanical waves travel fastest
  through a vacuum, then slower through gases, then
  liquids and slowest through solids
• Two perpendicular transverse waves

10
Electromagnetic Wave
http//www.nrc-cnrc.gc.ca/obj/inms-ienm/images/res
earch_images/optical_comb/COMBFIG1.gif
11
Wave Speed

• Wave speed (depends upon the composition and
  character of the medium it travels through)

12
Two types of waves based upon direction of
vibrating particles

• Transverse Waves cause particles in matter to
  vibrate perpendicular to the direction of wave
  travel.
• Longitudinal Waves cause particles in matter to
  vibrate in the same direction of wave travel.
• http//www.kettering.edu/drussell/Demos/waves/wav
  emotion.html

13
TRANSVERSE WAVE
crest
One wavelength
amplitude
Rest position
trough
14
LONGITUDINAL WAVE
Compression (more dense)
Rarefaction (less dense)
one wavelength
15
Wave Characteristics

• Frequency (f) (the number of vibrations that
  occur in a given time)
• Hertz (Hz) ( of vibrations per second)
• High frequency waves produce waves with short
  periods and short wavelengths
• Period (T) (the time it takes for one wave cycle
  to pass)
• Seconds (s)
• The lower the frequency, the longer the period

16
Wave Characteristics

• Wavelength ? (lambda) (the distance between one
  point on a wave to the next identical point
  crest to crest, for example)
• Meters (m)
• The lower the frequency, the longer the
  wavelength
• Amplitude (longitudinal wavesthe tightness of
  the compression transverse wavesthe distance
  from the crest to rest position or from trough to
  rest position)
• Meters (m)
• The greater the amplitude of the wave, the more
  energy the wave transfers.

17
Frequency vs. Intensity

• Rate of vibration (frequency)
• Amount of energy (intensity)
• Amplitude (amount of displacement)
• loudness (relative intensity of sound)
• brightness (number of photons of light)

Turn up the volume--same frequencies, different
intensity
18
Why do waves become less intense away from the
source?

• Same amount of energy is spread out over greater
  and greater distances.
• Same energy at every point along a wave front.
• Also, simple harmonic motion of the particles can
  be dampened (or absorbed or transferred) by the
  medium (rubber, clay, springs, fluids in shock
  absorbers)

19
Graphics References

• http//www.cen.bris.ac.uk/civil/students/eqteach97
  /waves2.htm
• http//www.physics.sjsu.edu/facstaff/becker/physic
  s51/
• http//www.kettering.edu/drussell/bats-new/impuls
  e.htm
• http//www.physics.brocku.ca/courses/1p22/images/f
  16013.jpg