Waves

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Waves
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Deep Impact video snippet
CLICK HERE

• Notice the ripple formed when the comet hits
  the ocean
• How do you think the energy of the impact
  reached the land and cause destruction of
  infrastructure?

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Waves transfer energy, not matter

• Ripple tank and Slinky demo

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Physical characteristics of wave

• Wavelength distance from one crest to the next
  crest or from one trough to the next trough
• Amplitude largest displacement of the particle
  in the medium from its equilibrium position
  (displacement 0)

crest
Equilibrium position
trough
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Physical characteristics of a wave

• Frequency (f) The number of waves produced in
  1second
• Note units for frequency is hertz or Hz
• Period (T) The time taken to produce one
  complete wave (ie covers one wavelength)
• f
• http//www.surendranath.org/Applets.html
• waves transverse waves

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Wave motion

• Motion of mechanical wave (as opposed to
  electromagnetic wave) due to vibration of
  particles in a medium
• Transverse vibration of particles perpendicular
  to direction of wave propagation (wave motion)
• Longitudinal vibration of particles parallel to
  direction of wave propagation (wave motion)
• http//www.cbu.edu/jvarrian/applets/waves1/lontra
  _g.htm
• Note that a medium is required before a
  mechanical wave can propagate!

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Longitudinal vs Transverse waves

• Slinky demonstration

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Lets do the Kallang Wave!
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Speed of waves

• Recall speed
• So for waves,
• speed v distance covered
  in 1 wavelength
• time taken to cover 1 wavelength
• Recall f
• so speed of waves v
• Speed equation for waves v f l
• Note that speed of
  waves ? speed of vibration of
  particles in medium
• http//www.surendranath.org/Applets.html

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Ripples in water

• http//www.falstad.com/ripple/

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Lets play with the Slinky!
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Worksheet on Stadium Wave

• A stadium wave typically has a wavelength of 5m.
  If the speed of
• the wave that moves round the stadium is 20m/s.
  Imagine you are
• one of the spectators in the crowd.
• How many waves do you expect to see being
  generated per second?
• f v/l So f 20/5 4 Hz
• 4 waves are generated per second
• How long does it take one wave to be generated?
• T 1/f So T 1/4 0.25s
• Given that the total circumference of the stadium
  is 800m, how long do you have to wait before the
  next round of wave reaches you?
• time taken distance/speed So wait time
  800/20 40s

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WAVES
Properties
Types of mechanical wave
Amplitude
Wave motion
Period T
Due to vibration of particles in medium
f 1 / T
Transverse
Longitudinal
Frequency f
More next lesson
Wavelength l
Wave equation v f l
Examples
Speed v
Ripples in water
Stadium wave