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