waves

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