By: Courtney Thomas
Lauren Goldfinger
Kelsey Tamburri
Sara Kielbasa
 Ocean tides are the
cycle of the rising
and falling level of
seawater.
 They are one of the
most reliable
phenomena this
world has to offer.
 There are now even
charts that show
when high and low
tide will be each day
 Tides are actually waves that
have very long periods and
move through the ocean. Tides
will start in the ocean and work
their way in towards the coast
lines.
 When the crest, or highest part
of the of the waves reaches the
coast it is high tide, and when
the trough of lowest part of the
wave reaches the coast it is low
tide.
BUT the real question is HOW DO
THEY WORK????
What is it that causes tides to happen?
GRAVITY! The gravitational force between the earth and the moon,
and the earth and the sun causes the tides.
•
•
The moon has more of an
effect on ocean tides than the
sun. The sun is actually half as
effective as the moon at
causing tides even though its
pull on the earth is 180 times
greater. So why is this?
This is because the of the great
distance between the Earth
and the Sun!
• The moon creates two bulges on opposite sides of the earth
that create high tides.
• Because the force of gravity is greater when the distance is
smaller, the gravitational force between the Moon and Earth
is stronger of the side of the earth closer to the moon.
• One the opposite side the force of gravity is much smaller
because the distance is much greater. The lack of a strong
pull makes this water bulge away.
• On the two sides perpendicular to the bulges is where the low
tide will occur.
The picture
summarizes what we
have talked about so
far. Both the sun and
moon have a
gravitational pull on
the earth, however,
the sun's is much
smaller. The side of
the earth that is
nearest the moon,
and opposite the
moon have the
bulge, which is high
tide. The sides
perpendicular to
those are pulled in
towards the earth
because they have
little pull, which
creates low tides.
Why is it that there are two high tides and two low tides a
day???
•
•
The reason there are two high tides and two low tides everyday are
because the earth rotates! It rotates one time every 24 hours.
Because of this rotation, one spot on the earth will be closest to the
moon, creating a high tide. 12 hours later that same spot will then
by opposite to where it was, farthest from the moon, which creates
another high tide. In the middle of the 12 hour intervals the spot
will be at one of the spots of low tide. Hence why about every 6
hours there will be either a high or low tide, and why there are two
cycles of tides per day.
Why do the times of high and low tide change
everyday???
•
•
Throughout the day the Earth rotates 360
degrees in 24 hours, so that means it rotates 180
degrees in 12 hours. The Moon is also rotating
though.
The moon rotates 6 degrees around the earth
every 12 hours, or 12 degrees in one day. This
makes it so that a high tide occurs once every 12
hours and 25 minutes. So, the two-high-tide
cycle is actually 25 hours and 50 minutes. This
makes it so that high and low tide are not the
same time everyday.
If the sun’s gravitational pull is
less then the moon’s then when
does it actually effect the
tides????
• Sun tides are only about half
as high as lunar, or moon
tides are.
• The main times that the sun
plays a noticeable role in
tides is during neap and
spring tides.
• At certain periods throughout
the cycle of the moon, the
moon, sun, and earth all align.
This happens during full and
new moons, which is about
every 14-15 days.
• When this happens it creates
more extreme tides, so higher
high tides, and lower low
tides.
• When the gravitational pulls of
the sun and moon are
perpendicular to each other, it
creates neap tides. This is when
the moon is halfway between
and new and full moon.
• When this happens it creates
less extreme tides. So lower
high tides, and higher low
tides.
• Tides are not as cut and dry as they seem. There are over 400
variables that affect the times, size, and number of times at
any one place or latitude!!!
• Some other variables that affect tides are:
•
•
The tilt of the earth
The geometric location of the moon and sun to a place
• Even though the bulges
are considered equal
the earth’s tilt causes
the high and low tides
in most places to
actually be unequal
• The geometric relationship of the moon and sun to a place
causes three types of tides:
•
•
•
Diurnal: one high and one low tide per day
Semi-Diurnal: two high and two low tides per day
Mixed: the high tide and low tides differ.
• These various types of tides happen in different areas of the
world
http://www.youtube.com/watch?v=kHvBUDk7kkQ
• The text book: “Conceptual Physics” by Paul G Hewitt
• http://oceanservice.noaa.gov/facts/tides.html
• http://www.google.com/imghp?hl=en&tab=wi
• http://science.howstuffworks.com/environmental/earth/geo
physics/tide-cause.htm
• http://www.enchantedlearning.com/subjects/ocean/Tides.sh
tml
• http://www.physicalgeography.net/fundamentals/8r.html