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OS102 > Waves > Flashcards

Waves Flashcards

1
Q

What is a transverse wave?

A

A wave in which the medium vibrates at right angles to the direction of its propagation

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2
Q

What is a longitudinal wave?

A

A wave vibrating in the direction of propagation

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3
Q

What is the height in terms of waves?

A

Vertical distance between crest and trough

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4
Q

What is a wavelength?

A

Horizontal distance between successive crests

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5
Q

What is a period in terms of waves?

A

Time interval between successive crests passing a point

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6
Q

What are the forces involved in the generation of waves?

A

Generating force and restoring force

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7
Q

What does the generating force do?

A

Disturbs from equilibrium state e.g. wind stress

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8
Q

What does the restoring force do?

A

Restores to equilibrium state e.g. gravity (surface tension at small scales e.g. capillary)

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9
Q

What does energy/size of waves depend on?

A
  • Wind speed
  • Wind duration
  • Fetch
  • Original sea state
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10
Q

What does the energy/size of waves depend on for large fetch and duration?

What does the size of waves depend on?

A

Size of waves (Hs) depends only on wind speed (W)

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11
Q

How do deep water waves work?

A
  • Water particle orbits are circular
  • Forwards beneath crest, backwards beneath trough
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12
Q

What is true when particle orbits are closed?

A
  • → No net flow of water
  • Energy and momentum transferred by waves
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13
Q

What is true at the surface and for larger waves?

A
  • Particle orbits are open
  • → Net forwards flow of water (Stokes Drift)
  • Mass transport of water due to waves
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14
Q

How do shallow water waves work?

A
  • Particle orbits influenced by seabed
  • Orbits compressed in vertical → ellipses
  • To and fro motion at the seabed
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15
Q

What is true of waves generated by storm winds?

A

Storm winds are unsteady and of variable direction, which means that the waves generated are:

  • ‘Forced’ waves
  • Irregular
  • Mixed characteristics
  • Known as “SEA”
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16
Q

What are ‘free waves’?

A

Waves away from the storm centre

17
Q

What is the Deep Water wave formula?

A

L = wavelength, T= wave period, C= phase speed or wave celerity

L = gT^2 / 2𝝅 and C = L/T gives C = gT / 2𝝅

18
Q

What is dispersion?

A
  • Longest waves travel fastest and run ahead – swell
  • Shorter waves follow behind

= Waves become sorted by length = DISPERSION

19
Q

What do waves tend to travel in?

A

Wave groups

20
Q

What is true of wave groups?

A
  • Propagate at group speed
  • Arise from interaction of waves with similar characteristics
  • Individual waves move through group from back to front
21
Q

What is the equation for wave groups in deep water?

A

Phase speed (C) = speed of individual wave crest
Group speed (CG) = speed at which wave energy propagates

C↓G = C/2 → C↓G = gT/4𝜋

22
Q

What happens during shoaling?

A

As waves enter shallowing water (from deep), the waves interact with the seabed and particle orbits are compressed = waves slow down

23
Q

What is the shallow water wave formulae?

A

C = (square root)gD

C = L/T

(D= water depth, C= speed of individual wave crest, L= wavelength, T= wave period0

24
Q

What is true of a wave crest’s orientation to the shore?

A

Wave crests tend to be parallel to the shore due to reaction

25
Q

What is true for oblique incidence waves?

A

Shallow end of wave slows fist

Wave crest bends round

26
Q

What does refraction do?

A

Refraction focuses wave energy:
- Towards shoals and headlands
- Away from deeper areas and bays

27
Q

Why does breaking occur?

A

In very shallow water, waves become too steep

28
Q

What are the types of breaker waves?

A
  • Spilling
  • Plunging
  • Surging
29
Q

What is true of spilling breaker waves?

A

Slow energy release (flat beach)

30
Q

What is true of plunging breaker waves?

A

Rapid energy release (steep beach)

31
Q

What is true of surging breaker waves?

A

Wave breaks at shoreline

32
Q

What is true of oblique incidence in breaking waves ?

A

Water is pushed forwards when waves break

Oblique incidence
→ Pushes water along shore
→ Longshore current

33
Q

What is true of normal incidence in breaking waves?

A

Water is pushed forwards when waves break

Normal incidence
→ Piles water up on the shore
→ Return flow offshore
→ Undertow or rip current

OS102 (13 decks)

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