21.3 Tides
Tides
Section 21.3
Tides
· daily changes in the water level of the oceans
· causes
Newton's law of gravitational pull of the moon on
Earth and its waters
sun plays a much smaller role because it is much
farther away
Tidal Bulges
· moon's gravity causes the water to bulge on the
side of the Earth nearest the moon
· b/c the solid Earth is also pulled toward the moon a
slightly smaller bulge is created on the opposite side
of Earth
· high tide - tidal bulge
· low tide - halfway between the high tides
Behavior of Tides
· all oceans pass under the moon every 24 hours and
50 minutes
if high tide was at 4:00pm, high tide would occur at
4:50pm tomorrow
· 2 tidal bulges every 24 hours and 50 minutes
2 high tides and 2 low tides daily
· tidal range - difference in the level of ocean water
during high tide and low tide
1 What is the main cause of ocean tides?
A
sun's gravitational pull on ocean water
B
moon's gravitational pull on ocean water
C
wind-driven wave energy
D
density differences
2 If high tide occurs are 3:30pm today,
when will high tide occur tomorrow?
A
3:30pm
B
4:20pm
C
4:30om
D
3:30am
21.3 Tides
Spring Tides
· occurs during new and full moons
· sun and moon are aligned and their gravitational
forces are added together
· higher high tides and lower low tides
· largest daily tidal range
New
moon
Neap Tides
First
Quarter
· occurs during 1st and 3rd quarter moons
· sun and moon are at right angles and
their gravitational forces oppose each
other
· daily tidal range is small
Full
moon
Third
Quarter
3 The greatest tidal range occurs during
neap tides when the sun, Earth, and
moon are in alignment.
True
False
4 High tide is also known as
A
slack water
B
ebb tide
C
flood tide
D
roll tide
Tidal Currents
· the horizontal flow of water towards and away from
the coast as a result of the rise and fall of tides
· flood tide - water flows toward the coast (high tide)
· ebb tide - water flows toward the ocean (low tide)
· slack water - time between flood and ebb tides