Waves Flashcards
wave
Disturbance caused by the movement of energy from a
source through some medium (solid, liquid, gas)
no movement of mass
classified by disturbing force, restoring force, and wavelength
progressive wave
a wave of moving energy in which energy moves in one direction across the surface of the medium
orbital wave
a progressive wave in which particles of the medium move in closed circles
water particles move in orbits, transmitting energy from particle to particle
motion is negligible below a depth of 1/2 the wavelength
at that depth, orbits are only 1/23 the diameter of those at the surface
wave height
Vertical distance between a wave crest and adjacent trough
wavelength
Horizontal distance between two successive crests (or troughs)
wave period
Time it takes for a wave
to move a distance of one wavelength
wave frequency
Number of waves
passing a fixed point per second
celerity
speed
C=L/T
longer wavelength = faster wave
only depends on the local water depth
deep water waves
Waves moving through water deeper than half their wavelength (L<2D)
→ The wave does not “feel” the bottom; orbits are circular
only capillary and wind waves CAN be deep water waves
shallow water waves
Waves moving through water shallower than 1/20 their original wavelength (L>20D)
→ The wave does “feel” the bottom; orbits are not circular (elliptical to flat)
formation of wind waves
Wind waves grow from capillary waves
- Capillary waves form as wind friction stretches the water surface and as surface tension tries to restore
its smoothness
- Capillary waves are always nearly present on the ocean (“ripples”)
- Capillary waves contribute to the transfer of wind energy into the water
→ As a result capillary waves progressively grow into wind waves (L > 1.74 cm)
Wind waves become larger if the wind continues to blow and waves remain in deep water (L < 2D)
- If winds get faster, more energy is input to the wave whose height grows
→ Wavelength (L) and wave period (T) increase proportionally
sea
Irregular peaked waves in the area of wind-wave formation
→ Chaotic surface is formed by simultaneous wind waves of many wavelengths, periods, and heights
wave steepness
Ratio of wave height to wavelength (H/L)
→ Wind waves have a wave steepness of maximum 1:7
→ If wave steepness gets greater, then waves break (whitecaps)
fetch
The uninterrupted distance over which the wind blows without a significant change in direction
fully developed sea
The maximum wave size theoretically possible for a wind of a specific strength,
duration, and fetch
Dispersion
Waves with longer wavelengths move faster
→ These waves leave the area of formation sooner than their smaller counterparts
→ The process of wave separation is called dispersion
swell
Mature wind waves of one wavelength that form orderly undulations of the ocean surface
surf beat
Big “sets” of waves expected by surfers between calm intervals
→ Results from constructive and destructive interferences of wind waves
rogue/freak wave
Unexpected huge wave that suddenly erupt from a moderate sea
→ Higher wave than the theoretical maximum wave capable of being sustained in a fully developed sea
→ Results from constructive interference
surf
Turbulent mass of agitated water rushing shoreward during and after the break
surf zone
Region between the breaking waves and the shore
Slope of the bottom
plunging wave - a breaking wave which forms an air-filled tube
→ Gradually shoaling bottoms can sap waves of their strength
Composition of the bottom
Energy of wave lost through interaction against bottom
→ Rough bottoms will extract more energy than smooth bottoms
refraction
Slowing and bending of progressive waves in shallow water
→ The part of the wave line in shallow water slows down
→ The part of the wave still in deeper water continues at its original speed
→ The wave line bends (refracts)
- The refracted waves break in a line almost parallel to the shore
diffraction
Propagation of a wave around an obstacle
→ Unlike wave refraction which depends on a wave’s response to a change in speed
→ Wave diffraction depends on the interruption of the wave trains by an obstacle
reflection
Occurs when waves “bounce back” from an obstacle they encounter
→ If incoming wave strikes the obstacle at a right angle, the wave energy is reflected back parallel to
the incoming wave
→ More commonly, waves approach the shore at an angle, causing wave energy to be reflected at an
angle equal to the angle at which the wave approached the obstacle
→ Reflected waves can cause interference with oncoming waves
internal waves
Subsurface wave forming at the boundary between water layers of different densities
→ Occurs in the ocean at the base of the pycnocline
- Internal waves are generated by wind energy, tidal energy and ocean currents
- Internal waves move more slowly than waves at the surface because the density difference between the two media is smaller
mix nutrients and trigger blooms
affect submarines and oil platforms
tsunami
Long wavelength (up to 200 km), shallow-water progressive wave caused by the rapid
displacement of ocean water
- Tsunami can be caused by sudden, vertical movement of Earth along faults (seismic sea waves), landslides, icebergs
falling from glaciers, volcanic eruptions, asteroid impacts, etc
tsunami propagation
As shallow water waves, tsunami are affected by the contour of the bottom and are commonly refracted
→ Wave is guided by mid-ocean ridges
→ Where depths are shallower, waves are slower, and energy becomes focused
