Vibrations and Waves

1
Vibrations and Waves

• Physics 1010
• Dr. Don Franceschetti
• November 17, 2003

2
Wiggles

• A vibration is a wiggle in time.
• A wave is a wiggle in space in time
• A pendulum is a vibration
• Period depends on length only
• Has an oscillatory motion
• Also called simple harmonic motion
• Traces out sine curve
• Amplitude is maximum displacement
• Wavelength distance from one crest to another

3
Frequency and all that

• Period is repeat time, in seconds
• Frequency 1/period, measured in cycles per
  second or hertz (Hz).
• Kilohertz (kHz)
• Megahertz (MHz)
• Gigahertz (GHz)
• Terahertz (THz)

4
Wave motion

• At any point in space, motion in that of a single
  oscillator.
• Point of maximum amplitude (crest) moves with
  wave speed.
• Wavelength is distance between crests.
• Wave speed wavelength x frequency
• Waves can be transverse or longitudinal

5
Earthquake waves

• P waves, longitudinal (push-pull)
• S waves, transverse (side to side)

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Interference

• Two waves traveling through same region of space.
  Amplitudes add by superposition.
• Constructive interference (crests match up)
• Destructive interference (crests and troughs
  match up)

7
Standing wave

• Rope tied to wall, wall doesnt move
• Wall reflects pulse (inverted)
• Incident and reflected wave form standing waves
• Nodes are stationary points.
• Antinodes ape points of maximum motion.
• Basis of stringed instruments.

8
Doppler Effect

• Christian Doppler demonstrated with trumpeters on
  railroad flatcar.
• Common experience with ambulances, firetrucks,
  etc.
• Crests bunch together on approaching side, spread
  apart on retreating side
• Doppler radarspeed guns, weather

9
Doppler Shift in Astronomy

• Kirchhoffs rules
• Dilute hot gases emit light at precise
  wavelengths determined by chemical composition
• Dense hot gases emit a cavity radiation spectrum
• Dilute gases in front of a stellar surface absorb
  at precise wavelengths detd by chem comp
• Red/blue shifts in wavelengths tell whether
  object is approaching or receding from us.
• Used to study motions within milky way.
• Distant galaxies are all redshifted, evidence
  for big bang

10
Bow Waves

• At speed of sound waves pile up in front of
  source
• Bow waves in 2D
• Shock waves in 3D

11
Chapter 19 Review

• Questions 4,5,6,7,8,9,10,11,12,13,14,17,18, 21,
  22
• Exercises 1,2,3,8,10,12,19,21,24,29, 30
• Problems 1,2,4,5,7