Tide Activity Using Real Tide Data

Dr. Pamela Gore
Georgia Perimeter College

Objectives

To use the Internet as a source for real and current data.
To demonstrate the rhythmic patterns of tides throughout a month.
To chart the relationship between tides and phases of the moon.

Materials Needed

A computer with Internet access and spreadsheet software (such as Excel)

Background Information

In most parts of the world, the difference between high and low tide amounts to only a few feet. Nevertheless, this change in water level still is enough to be very important in some areas. In many places at low tide, the water is too shallow to allow boats to move effectively into an out of harbors, whereas at high tide it is deep enough for them to do so. Because of their effect on navigation, tides have been studied for many years, and today physical oceanographers know quite a bit about their causes and characteristics.

Procedure

Go to St. Simons Island Tide Table, or use the tide data on this page: St. Simons Tide Data.

What is the time interval between two successive high tides?
How many high tides are there per day? ___________
How many low tides are there per day? ___________
Pick one high tide, and find the next low tide that day. How long did it take for the tide to go out?
Pick one low tide, and find the next high tide that day. How long did it take for the tide to come in?
a. Are the two times the same? ___________
b. Which takes longer? ___________
c. Why?
Graph the level of the high tides in feet for a month.

You may do this on a computer with a spreadsheet program, or you may do it on graph paper. If you are going to use a spreadsheet program, use your mouse to select and copy the tidal data (high tide level in feet) for one month. Paste the data into your spreadsheet program. In your spreadsheet program, make a graph of the level of the high tides. You may make a scatter plot, column plot or line plot.
Plot the days of the month along the bottom of the chart (x axis), and the tide level along the vertical axis (y axis). What kind of patterns do these data reveal?
Tides are cyclical and closely follow the phases of the moon. During the new and full moons, the distance between the high and low tides increases, which means that high tides get higher and low tides get lower.
1. From your graph, pick the date that has the highest high tide. ____________________________
2. What phase of the moon is associated with this high tide? ________________________
3. From your graph, pick the date at the second highest peak of high tide. __________________________
4. What phase of the moon is associated with this high tide? _________________________
5. From your graph, pick the date that has the lowest high tide. _____________________________
6. What phase of the moon is associated with this high tide? _________________________
7. From your graph, pick the date that has the second-lowest trough on the curve for the lowest high tide. _____________________________
8. What phase of the moon is associated with this high tide? _________________________
The alignment of the Sun, Moon and Earth affects how high the tides will be.
1. Sketch the alignment of the Sun, Moon and Earth at new moon.
2. Sketch the alignment of the Sun, Moon and Earth at full moon.
3. From your sketches, which lunar phase would you expect to be associated with the highest tides? _______________________
4. Is this what you observed with your data?
5. Sketch the alignment of the Sun, Moon and Earth at first quarter moon or last (third) quarter moon.
6. Explain why this alignment results in lower high tides than at full moon or new moon.
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For further study:

Visit the NOAA Tides Online website and investigate tides in another area, such as at Oregon Inlet, North Carolina. You can see a graph of the high and low tides throughout the day.

How does the height of the tides at Oregon Inlet, North Carolina compare to the height of the tides at St. Simons Island, Georgia?
Can you think of any reasons to explain the difference?
Check the height of the tides at Key West, Florida. The curve has a different shape, with successive peaks being very different in height. Sketch the shape of the curve.
Can you speculate as to the reason for this shape?
Check the tidal curve for Pensacola, Florida on the Gulf of Mexico.
1. What do you notice that is VERY DIFFERENT about its tides, compared with Georgia and North Carolina?
2. How many high tides are there per day? ___________
3. How many low tides are there per day? ___________
4. What is the tidal range? ___________
Check the tidal curve for Eastport, ME.
1. How many high tides are there per day? ___________
2. How many low tides are there per day? ___________
3. What is the tidal range? ___________
  
  Can you speculate as to the reason for this shape and the difference in tidal range?
Now let's take a look at some tidal curve for the west coast of the U.S.
1. Examine the tidal curve for Seattle, Washington, and sketch it in the box below.
2. How many high tides are there per day? ___________
3. How many low tides are there per day? ___________
4. What is the tidal range? ___________
  
  Can you speculate as to the reason for this shape?
Examine the tidal curve for San Francisco, CA, and sketch it in the box below.
Can you speculate as to the reason for this shape?
Examine the tidal curve for Ketchikan, AK.
1. How many high tides are there per day? ___________
2. How many low tides are there per day? ___________
3. What is the tidal range? ___________
Examine the tidal curve for Hilo, HI.
1. How many high tides are there per day? ___________
2. How many low tides are there per day? ___________
3. What is the tidal range? ___________
Why might the tidal range in Hawaii be so different from the tidal range in Alaska?

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Page created by Pamela J.W. Gore
Georgia Perimeter College,
Clarkston, GA