Objectives
The student will be able to:

• Describe how sea levels are constantly changing with daily and monthly cycles.
• List some causes and effects of tidal changes.

Lesson Description
Through this lesson, students should gain a basic understanding of ocean tides and why they occur. Students will begin by examining elevation and sea level. They will discover that sea level is not constant, as tides rise and fall daily. Students will visit links to gather information and develop a graph of tidal data. They will use this data to discover that tides are controlled by the phases of the moon and the moon's gravitational pull.

SUGGESTED TIME FOR ENTIRE UNIT: 1 week (5 days)

Pre-Assessment
The pre-assessment is designed to assess students' knowledge regarding the stated lesson objectives. There are also control questions that are not directly associated with the lesson. Their purpose is to act as a measuring stick to determine the degree to which the students actually learn from the lesson.

• To access a printable version of the pre-assessment to view or copy for students, click here.
• To view or print a copy of the answers to pre-assessment questions, click here.

Post-Assessment
The post-test is designed to assess students' knowledge of the stated objectives after they have completed the entire lesson. As with the pre-assessment, a series of control questions are also included in the post-assessment. Their purpose is to determine the degree to which the students learn from this lesson.

• To access a printable version of the post-assessment to view or copy for students, click here.
• To view or print a copy of the answers to post-assessment questions, click here.

Activities and Assignments
Materials
None

Optional:
Handouts of the assessments and activity instructions may also be created before the lesson to help students with the unit.

Procedures
Throughout the unit, the teacher may guide the students through the information by projecting the lesson onto a screen. Another option is to have students work on the unit themselves, with the teacher monitoring as they navigate through the site on the computers individually or in small groups.

1. Through the Introduction, students will learn about sea level changes. They will view photographs of high and low tides in New Brunswick and in Texas. And be asked to think about what could cause the changes in sea level.
   
   
2. The Presentation defines elevation and sea level, setting the stage for learning more about tides. Students will be able to click on links throughout the presentation to gain a better understanding of the concepts, as well as to answer their own questions. Through viewing tidal data about Galveston Bay, students will notice how tides change on a daily basis. They will discover how sea level is measured and the effects of sea level on recreation and business. Students will also complete journal entries/activities as they read through the presentation. They can record observations and answers about their knowledge on each of these journal pages (that can be printed and distributed to students):
   Journal Entry 1
   Journal Entry 2
   Journal Entry 3
   Journal Entry 4
   The teacher's answer key for these pages can be accessed here.
   
   
3. The Activity involves graphing tidal data and comparing the information on the graph to the lunar phases. Students will create a graph of a month's worth of tidal data. This graph will be a line graph that has peaks and dips. They will then view a chart of the lunar phases for the same month. Students should notice that the peaks and dips are more pronounced when the moon is in its full or new phases. The peak and dips are less pronounced when the moon is only half full. Through this activity, students should realize that the highest and lowest tides every month occur during the full and new moon phases. The smallest changes between high and low tide occur during the half moon phases each month.

Tools and Resources
Hardware used in this lesson:
Computer: With keyboard, mouse, and operating system such as Windows 95
Printer- (optional): For printing out instructions and assessments for the class or for printing student work (graphs)
Projector- (optional): Such as a Proxima projector, that is capable of projecting computer images onto a screen so that the whole class may view the lesson along with the teacher
Software used in this lesson:
Microsoft EXCEL: To create graphs of tidal data
Microsoft WORD: To view printable documents and print them
Microsoft Internet Explorer or Netscape Navigator: To view the lesson, access the links, data, and pictures
Web sites used in the lesson:
Ask Yahoo: This site describes how sea level is calculated and is used in the Presentation of the lesson.
Anchorage, AK: This site has a photograph of the water level measuring device and station in Alaska.
Satellite: This site describes how sea level is measured using a satellite. It is very complicated and can be an optional site for students to visit.
Why Sea Level Changes: This link brings up the NOAA page about tides and what causes them. It is a long page, but the students should read the first to paragraphs to access information about tidal changes.
Moon Phases: Clicking on this link will open up a chart that is to be used with the activity. The lunar phases for the month of February 2000 can be brought up so that they may be compared with the tidal data from the students' graphs. The chart will show the full, new, and half phases of the moon during that month.
More Information on Gravity and Tides: This site provides a written description of how the gravity of the sun and moon affect the tides.

Extensions and Modifications (Optional)
As an extension, some students may want to see the source for the data from the spreadsheet. The teacher may have students access this information, along with the steps we followed to build the spreadsheet. You can access an online version of this challenging extension activity at http://oceandrilling.coe.tamu.edu/curriculum/Sea_Level/Tides/ Extension_Activity_Pages/ activity.html. Other options to extend the lesson include having students view related links and pages and share their findings with the class.
This lesson may be modified in its presentation. The teacher may want to do the lesson from the computer, projecting the information on a screen in front of the class and asking questions along the way. Presenting the lesson in this way may assist students who are not comfortable with navigating around the Internet or in classrooms where there are few computers or Internet connections.

Standards Targeted