Answer 3:
The fluctuations of tides here on Earth are
not only a function of forces imposed by the moon,
but also by those forces imposed by the sun!
Both the moon and the sun exert a gravitational
pull on the earth. This gravitational pull is
actually what creates our tides. More
specifically, we have two main types of tides that
we experience here on earth: spring tides and
neap tides. Spring tides occur every new or
full moon in which the moon forms a line with the
earth and the sun (the moon is situated right in
between earth and the sun). When this occurs, the
moons gravitational pull on the earth is
strengthened by the added gravitational pull of
the sun, as can be seen in the picture below (from
physicalgeography.net).
spring tides
During these spring tides, the change from the
lowest tide to the highest tide (and vice versa)
is at a maximum, meaning this is when we
experience extremely low tides and extremely high
tides.
Neap tides occur halfway between the new and full
moon when the sun and moon are at a 90o angle to
one another. When this happens, the sun’s
gravitational pull competes with the moon’s
gravitational pull so that the range in high and
low tides is quite small (see picture below from
physicalgeography.net).
neap tides
This gravitational pull that the oceans
experience theoretically should affect all sources
of water on Earth. In reality, the size of
lakes, puddles, and streams are simply too small
for these gravitational forces to have a large
effect. The Great Lakes are quite large and do
experience small tide changes, however, most other
lakes and bodies of water are much more affected
by changing inflows of water from rivers and
streams as well as wind - both of which can change
the height of the water much more dramatically
than gravitational influences. It takes a large,
interconnected body of water to significantly be
affected by gravitational forces that cause tidal
changes.
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