WAVES
• disturbance caused by the movement of energy from a source through some medium (solid, liquid or gas).
WAVES
• The energy is moving at the speed of the wave, but NOT the water
WAVES
• The parcel of water moves in a circular motion = orbit
Fig. 9-3, p. 201
WAVES
• Because the wave form moves forward these are called progressive waves
Fig. 9-2, p. 201
Orbits
• The diameter of the orbits diminishes rapidly with depth• Wave motion in deep water is negligible past ½ the wavelength
Stoke’s Drift or Mass Transport
• Small net movement of water in the direction of the wave
Classifying Waves
• disturbing force = the energy that cause waves to form
• restoring force = the dominant force trying to return surface water to flatness
• wavelength
Table 9-1, p. 202
Figure 8.9
Deep vs Shallow Water waves• The orbits of water molecules in a wave are
circular only when the wave is in deep water
• A wave cannot “feel” the bottom if it is in water deeper than ½ its wavelength
• = a deep water wave
Figure 8.7a: Deep Water Wave
Figure 8.7b
Transitional waves = travel through water deeper than 1/20 their wavelength and shallower than ½ its wavelength
Figure 8.7c
Shallow water waves = moving in water shallower than 1/20 it wavelengthWater at the bottom moves back and forth
Deep vs Shallow Water Waves• ONLY WIND WAVES CAN BE DEEP
WATER WAVES
How waves break at shore...• A deep water waves feels bottom and becomes a
transitional wave then a shallow water wave
• orbits become elliptical
• crests become peaked so wave height increases
• Waves in front slow down so wave length decrease
How waves break at shore...• The wave becomes too high for its
wavelength and the wave breaks– Wave steepness is waveheight/wavelength– When H/L = 1/7, the wave breaks
• The surf zone is the region between the breaking waves and the shore.
How large do wind waves get?
• Depends on – wind strength– wind duration– fetch (distance over which wind blows)
• Waves spread out (dispersion) based on size (large waves move faster)– Capillary waves … wind waves…fully
developed seas…swell
Figure 8.10
Fig. 9-9, p. 207
Fig. 8.12
Highest wave: 1933 – in Pacific during a strong storm: strong wind in one direction for days…112ft (34 m)
INTERFERENCE
• Destructive interference = cancellation effects of subtraction– When a wave crest and another wave’s trough
coincide
INTERFERENCE
• Constructive interference = addition effects that form large crests and deep troughs– When crests coincide
Figure 8.15
Figure 8.16
Fig. 9-13 (a-b), p. 209
Fig. 9-13c, p. 209
Constructive Interference can cause “Rogue Waves”
Fig. 9-16, p. 211
A 20 m (66 ft) wavein Hawaii
Wave Refraction
• When waves do not approach parallel to shore…
• The wave line will bend to become more parallel to shore
Figure 8.19a
Figure 8.19b
Figure 8.19c
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