Graphing the Tides

In this activity you will plot a month's worth of tide data and use the resultant graph to answer questions.

  1. Examine the tide data table on the back of this sheet. Find the highest high tide and the lowest low tide in the month. What is the difference between these two heights?
  2. Draw and label the axes for the graph. The x-axis should be day of the month and the y-axis should be height of tide. Look in the table at the highest and lowest numbers for day and height to determine what scale to use for the axes. For many locations, a scale where each line on the x-axis represents one day and each line on the y-axis represents 1/2 meter will work well.
  3. Now you are ready to plot your data. First plot the height of the first high tide of the month. Then skip the next high tide and plot the third high tide (this has been done for you). Continue this way, plotting every other high tide. When you finish, you should have one data point for high tide on each day of the month.
  4. Next, repeat the procedure in Step 6 for low tides.
  5. Label the spring tides and neap tides on your graph. (HINT: Remember that there are two spring tides and two neap tides each month.)
  6. On your graph indicate where the New Moon, 1st Quarter, Full Moon and 3rd Quarter Moon would appear in the sky.

Analysis

1. What type of pattern do your graphs show?

2. Is the difference in height between high tide and low tide on a given day fairly constant over a month? Explain why or why not.

3. Are the dates of the highest high tide and highest low tide the same? Explain your results.

4. What is the date of the highest high tide in your graph? What is the date of the lowest low tide? Explain your results.

5. How many days are there between the two spring tides? Between the two neap tides? Explain your results.

6. What do you think the phase of the moon will be on the date of the highest high tide? On the date of the lowest high tide?

7. Use your results from Step 6 to explain how the phase of the moon is related to the height of high tide.

Tidal Data

Date / Day / High Tide / Low Tide / Phase of Moon
2/8/09 / Sun / 13.1 / 1.3 / Full
2/10/09 / Tues / 13.6 / 0.5
2/12/09 / Thurs / 13.4 / 0.3
2/14/09 / Sat / 12.8 / 1.1
2/16/09 / Mon / 11.6 / 2.3
2/18/09 / Wed / 10.5 / 3.5
2/20/09 / Fri / 10.2 / 4.0
2/22/09 / Sun / 10.7 / 3.5
2/24/09 / Tues / 11.6 / 2.6
2/26/09 / Thurs / 12.1 / 1.8
2/28/09 / Sat / 12.7 / 1.3
3/1/09 / Mon / 12.8 / 1.3
3/3/09 / Wed / 12.2 / 1.7
3/5/09 / Fri / 12.0 / 2.3
3/7/09 / Sun / 12.2 / 2.2
3/9/09 / Tues / 13.0 / 1.2