Name: ___________________________
Science/Key/Block # _______
Date: _____________________________
Read in your book about tides in the chapter about Oceans!
Gravity is an imaginary pulling force between objects. Two things that
affect gravity are the size of the object and the distance you are from
that object. For example, Jupiter has more gravity than Earth, and Earth
has more gravity than the moon.
Since the moon is relatively close to the earth, there is a gravitational
attraction between Earth and the moon. The moon’s gravity causes tides
on Earth.
Earth
Moon
If you have ever spent a day at the beach, you probably noticed that
the level of the ocean at the shoreline did not stay the same during the
day. For about six hours, the ocean level rises on the beach. Then, for
another six hours, the ocean level falls. The rise and fall of the oceans is
called tides.
As the moon’s gravity pulls on the earth, it causes the oceans to
bulge. The oceans bulge in two places: on the side of the Earth facing the
moon and on the side of the Earth facing away from the moon. Each of
these bulges causes a high tide.
At the same time that the high tides occur, low tides occur between
the two bulges. The diagram below shows the positions of high tides and
low tides on the Earth.
Since the Earth rotates on its axis every 24 hours, the moon’s gravity
pulls on different parts of the Earth at different times of the day. So at a
given place on the Earth, there are two high tides and two low tides every
day. Since the moon rises about 50 minutes later each day, the high and
the low tides are also 50 minutes later each day.
Spring Tides
Spring tides are tides that are higher than normal during high tide or
lower than normal during low tide. Spring tides occur because the sun
and the moon are in a direct line with the Earth. The increased effect of
the sun’s gravity on the Earth causes the ocean bulges to be larger than
usual.
Su
n
Su
n
Neap Tides
Neap tides are high tides that are not as high as usual and low tides
that are not as low as usual.
During the first and last quarter of the moon, the sun, moon and Earth
are at right angles to one another. During this time, the tides are not as
high or not as low as usual.
Sun
Moon
Finally, the moon’s orbit around the Earth is an ellipse. This allows the
Moon to be at different distances from the Earth. When the Moon is
closer, the gravitational pull is greater. So, if it is full moon and the moon
is closer to the Earth, the tides will be extremely high or low.
Understanding Tides Notes…..
Tides are caused by the Moon’s _______________ pull. Since the oceans are
liquid water, they can move freely in the direction of the moon’s
gravitational pull.
Each ocean shore experience _____ high tides and _____ low tides per day...
Because the Earth spins on its axis once in a 24 hour period.
____________ Tides occur when the moon
and sun are aligned. The gravitational
force of both causes exceptionally tides
which cause beach erosion.
____________ Tides occur when
the moon and sun are at
________ angles to each other.
The resulting high tide is not as
high as it should be because of
the sun’s gravitational field.
Important notes: The size of a high
tide depends also on
____________________ features. For
example, the Bay of Fundy, off the
coast of Maine in Canada, has the
highest tides in the world due to its
unique geographical shape. At high
tide, waters in the bay rise 52 feet
above waters at low tide!
http://www.thehopewellrocks.ca/english/fundytides4.htm and http://curious.astro.cornell.edu/images/tides.jpg
TIDE QUESTIONS
Item # _11_
Name: ___________________________
Science/Key/Block # _______
Date: _____________________________
Directions: Use the “Tides” worksheet to answer the following questions:
1. What is gravity and what affects it’s strength? (complete sentence)
2. Since the moon is relatively close to the earth, there is a
____________________________ attraction between the earth and the moon.
4. What does the moon’s gravity cause on Earth? ___________________________
5. For about how many hours does the ocean level rise on the beach? _______ hrs
6. Then, for about how many hours does the ocean level fall? ________hrs
7. The rise and fall of the oceans is called ________________________________.
9. Draw a picture that shows the positions of high tides and low tides on Earth.
(you may redraw the picture in your notes)
13. What are spring tides and what causes
them? (complete sentence)
14. What are neap tides and what causes
them? (complete sentence)
Draw the position of the earth and moon
during a spring tide.
Draw the position of the earth and moon
during a neap tide.
Sun
Sun