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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
Classify: Tsunami
Generating force: - faulting of sea floor - volcanic eruption - landslide Wavelength: 200km
26
Classify: Tide
Generating force: - gravitational attraction - rotation of earth Wavelength: 20,000km
27
Classify: Capillary Wave
Restoring force: - surface tension Wavelength: < 1.7cm
28
Classify: Surface Gravity Waves
Restoring force: - gravity Wavelength: > 1.7cm
29
Wind waves, seiches, tsunamis, and tides are types of
Surface gravity waves
30
How do water particles move as a wave passes?
Forward circular motion / orbits where energy passes thru water but net movement of water particles is negligible
31
Wave base marks the ___ of the wave and can be calculated by ___
bottom (where orbitals disappear) wavelength ÷ 2
32
In open water, water particles have an orbital motion that ___ with depth
decreases
33
The orbital diameter of wave motion is equal to the
wave height (H)
34
Is there orbital movement below the wave base?
nope
35
What are deep water waves?
d >= L / 2 (water depth >= wave base) - waves don't feel the sea floor
36
What are shallow water waves?
d <= L / 20 - waves interact with sea floor - friction flattens orbits to oval shape
37
What is an intermediate wave?
L / 20 <= depth <= L / 2
38
The speed of deep water waves depend on ___ only
Wavelength
39
Equation to calculate the speed of a deep water wave
c = 1.25 √ L OR c= 2.56 x T in m/s!
40
Storms produce winds travelling in various directions, which generates winds with different ____
wavelengths
41
Due to a storm, the chaotic sea has ___ and the swell in front of it has ___ wavelengths
chaotic: many wavelengths swell: long wavelengths
42
How do deep water waves tend to travel?
in groups that have similar wavelengths
43
In the sea, complex swells result from what?
waves of diff wavelengths
44
describe the dispersion of deep water waves
- 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
waves are sorted by wavelength by the time they reach the shore, due to ____
dispersion
46
The speed of shallow & intermediate waves depends on ____ only
depth c = √gd c = 3.1 √ d
47
True or false: the speed of shallow & intermediate waves are affected by wavelength
false! they're affected only by depth
48
Shallow waves travel faster in ___ water and slower in ___
faster in deeper, slower in shallower cuz floor creates friction
49
What happens as waves approach the shore (move into shallower water)?
- 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
How does friction affect water moving past the ocean floor?
- decreases wave speed (c) - increases wave height (H) - some kinetic energy is lost
51
Waves break when
speed of water in crest > wave velocity (outrace bottom and falls forward) - when H/d ~ 3/4
52
How to calculate when a wave will break
H/L > 1/7 (0.14) - at 1/7, the wave does NOT break yet
53
T or F: waves are sorted by wavelength by the time they reach the shore
True Cuz dispersion

EOSC 114 (30 decks)

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