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TIDES

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TIDES periodic, short term changes in the height of the ocean surface at a particular place * Figure 10.2 A planet orbits the sun in balance between gravity and inertia. – PowerPoint PPT presentation

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Title: TIDES


1
TIDES
  • periodic, short term changes in the height of the
    ocean surface at a particular place

2
What causes tides?
  • a combination of the gravitational force of the
    moon and sun and the rotation of the earth
  • moon exerts greater effect than the sun

3
Tides are waves
  • longest waves with wavelengths of half the
    Earths circumference
  • High tide is the crest of the wave and low tide
    is the trough

4
Equilibrium Theory of Tides
  • Isaac Newton, 1600s
  • Would accurately describe tides on a planet
    uniformly covered with water
  • Does not consider the effects of continents,
    ocean basin shape and ocean depth
  • Explains the effects of the gravitational
    attractions of Earth, moon and sun

5
Fig. 10-2, p. 229
6
Fig. 10-2, p. 229
7
Fig. 10-2, p. 229
8
Fig. 10-3, p. 230
9
Fig. 10-4, p. 230
10
Fig. 10-5, p. 230
11
Fig. 10-6, p. 231
12
How tides occur...
  • The bulges stayed aligned with the moon as the
    earth rotates on its axis,
  • as points on the earth pass through the bulges,
    they experience high tide

13
Fig. 10-7a, p. 231
14
Fig. 10-7b, p. 231
15
Other factors affecting tides...
  • the moon rises 50 min. later each day
  • high tides occur about 50 min later each day.

16
Figure 9.8
17
Other factors affecting tides...
  • the moon moves each month from a position 28.5o
    above to 28.5o below the equator
  • leads to unequal tides a high high and a lower
    high that same day.

18
Fig. 10-9, p. 232
19
Fig. 10-10, p. 233
20
Figure 9.14
21
Influence of the Sun
  • only about 46 of that of the moon due to the
    large distance b/w the earth sun

22
Influence of the Sun
  • The effects of the sun and moon cause wave
    interference
  • constructive interferencehigher high tides and
    lower low tides spring tides
  • Maximum tidal range
  • destructive interferencelower high tides and
    higher low tides neap tides
  • Minimum tidal range

23
Figure 9.11
24
Figure 9.10
25
Fig. 10-12, p. 234
26
Dynamic Theory of tides
  • Laplace, 1775
  • considers ocean depth, continents, the shape of
    the basin

27
Tidal regimes
  • Semidiurnal tides two high tides and two low
    tides of nearly equal level each lunar day
  • Diurnal tides one high and one low tide each
    lunar day
  • Mixed tides when successive high or low tides
    are significantly different in height

28
Figure 9.16
29
Tidal currents
  • Rise and fall in sea-level as the tidal crest
    passes will cause currents
  • Water rushing toward shore due to rising
    sea-level is called a flood current
  • Water rushing away from shore is called an ebb
    current
  • Slack water a time of no current occurs at high
    or low tide

30
Figure 9.19
31
Figure 9.18 Bay of Fundy Largest Tidal Range
Extreme Tides Max tidal range about 17m or 56 ft
at northern end of Minas Basin
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