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EOSC 114 > Waves 1 > Flashcards

Waves 1 Flashcards

1
Q

What is a wave?

A

propagation of energy through a medium

  • medium itself barely moves
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2
Q

Ocean waves are generated by ___ or ___

A
  • wind
  • geological events (earthquakes, landslides, etc)
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3
Q

The net water motion of ocean waves is

A

zero, water particles rotate in place

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4
Q

What is wave height (H)

A

the vertical distance from crest to trough

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5
Q

How can we calculate Steepness?

A

H/L
(wave height / wave length)
- no units!

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6
Q

For a given wave height, shorter wavelengths lead to ___ steepness

A

higher

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7
Q

Period vs Frequency

A

period is time between successive cycles (sec)
frequency is number of cycles per second (Hz)

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8
Q

What is celerity?

A

speed of a wave in m/s
L/T
(wavelength / period)

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9
Q

the generating force creates

A

a disturbance in the fluid level

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10
Q

the restoring force tries to ___ but ___

A
  • remove/flatten out the disturbance
  • it overshoots and creates a trough
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11
Q

the ___ overshooting the ___ creates an oscillation

A
  • restoring force
  • initial generating force
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12
Q

Typical wavelength of waves generated by winds

A

60 - 150m

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13
Q

Typical wavelength of waves generated by geological events

A

200km
tsunamis!

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14
Q

Typical wavelength of tides

A

20 000km
that’s half the circumference of earth!

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15
Q

Waves generated by the gravitational pull of the moon and sun are called…

A

tides

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16
Q

What is the restoring force for small waves? (wavelength < ___cm)

A

< 1.7cm

Surface tension or cohesion of water created by H-bonds btwn molecules

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17
Q

What are the two kinds of restoring forces?

A
  1. surface tension
  2. gravity
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18
Q

If the generating force was a small object that dropped into the water, the restoring force would be…

A

surface tension

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19
Q

What is the restoring force for larger waves? (wavelength > ___cm)

A

> 1.7cm

Gravity: the weight of water in the CREST pulls the crest back down

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20
Q

Classification of waves can be based on (2 things)

A
  1. Generating force
  2. Restoring force
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21
Q

What is a generating force?

A

force that adds energy to the water

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22
Q

Classify: Wind Wave

A

Generating force:
- wind

Wavelength: up to 150m

23
Q

Classify: Seiche

A

Generating force:
- changes in atmospheric pressure (MOST important)
- storm surge
- tsunami

Wavelength: 1km

24
Q

What is the most important generating force for seiches?

A

changes in atmospheric pressure

25
Q

Classify: Tsunami

A

Generating force:
- faulting of sea floor
- volcanic eruption
- landslide

Wavelength: 200km

26
Q

Classify: Tide

A

Generating force:
- gravitational attraction
- rotation of earth

Wavelength: 20,000km

27
Q

Classify: Capillary Wave

A

Restoring force:
- surface tension

Wavelength: < 1.7cm

28
Q

Classify: Surface Gravity Waves

A

Restoring force:
- gravity

Wavelength: > 1.7cm

29
Q

Wind waves, seiches, tsunamis, and tides are types of

A

Surface gravity waves

30
Q

How do water particles move as a wave passes?

A

Forward circular motion / orbits
where energy passes thru water but net movement of water particles is negligible

31
Q

Wave base marks the ___ of the wave and can be calculated by ___

A

bottom (where orbitals disappear)

wavelength ÷ 2

32
Q

In open water, water particles have an orbital motion that ___ with depth

A

decreases

33
Q

The orbital diameter of wave motion is equal to the

A

wave height (H)

34
Q

Is there orbital movement below the wave base?

A

nope

35
Q

What are deep water waves?

A

d >= L / 2
(water depth >= wave base)

  • waves don’t feel the sea floor
36
Q

What are shallow water waves?

A

d <= L / 20

  • waves interact with sea floor
  • friction flattens orbits to oval shape
37
Q

What is an intermediate wave?

A

L / 20 <= depth <= L / 2

38
Q

The speed of deep water waves depend on ___ only

A

Wavelength

39
Q

Equation to calculate the speed of a deep water wave

A

c = 1.25 √ L
OR
c= 2.56 x T

in m/s!

40
Q

Storms produce winds travelling in various directions, which generates winds with different ____

A

wavelengths

41
Q

Due to a storm, the chaotic sea has ___ and the swell in front of it has ___ wavelengths

A

chaotic: many wavelengths
swell: long wavelengths

42
Q

How do deep water waves tend to travel?

A

in groups that have similar wavelengths

43
Q

In the sea, complex swells result from what?

A

waves of diff wavelengths

44
Q

describe the dispersion of deep water waves

A
  • waves with longer wavelengths travel faster and outruns the others
  • results in waves travelling in groups w/ similar wavelengths
  • long wavelength waves are more ahead of the storm
45
Q

waves are sorted by wavelength by the time they reach the shore, due to ____

A

dispersion

46
Q

The speed of shallow & intermediate waves depends on ____ only

A

depth

c = √gd
c = 3.1 √ d

47
Q

True or false: the speed of shallow & intermediate waves are affected by wavelength

A

false!
they’re affected only by depth

48
Q

Shallow waves travel faster in ___ water and slower in ___

A

faster in deeper, slower in shallower cuz floor creates friction

49
Q

What happens as waves approach the shore (move into shallower water)?

A
  • wave height (H) and steepness INCREASE
  • speed and wavelength decreases
  • period stays the same
  • orbitals flatten
  • waves break
  • some kinetic energy is lost due to friction
50
Q

How does friction affect water moving past the ocean floor?

A
  • decreases wave speed (c)
  • increases wave height (H)
  • some kinetic energy is lost
51
Q

Waves break when

A

speed of water in crest > wave velocity
(outrace bottom and falls forward)

  • when H/d ~ 3/4
52
Q

How to calculate when a wave will break

A

H/L > 1/7 (0.14)

  • at 1/7, the wave does NOT break yet
53
Q

T or F: waves are sorted by wavelength by the time they reach the shore

A

True
Cuz dispersion

EOSC 114 (30 decks)

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