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# Tides in the Chesapeake Bay (page 2)

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#### What causes tides?

Tides are caused by the gravitational pull of the sun and moon and by the rotation of the earth on its axis. As the earth spins, each part of the water is under the moon once about every 24 hours. The water bulging towards the moon makes the high tide. The centrifugal force causes another high tide on the opposite side of the earth. The centrifugal force is the force that pulls a thing outward from the center when it is spinning. This force pulls the water away from the earth to form a bulge while it is spinning.

#### What affects tides?

Tides are affected by the sun’s gravitational pull. The moon’s gravity also affects them. Although the sun is 27 million times larger than the moon, it is also 400 times further away. So the tidal force caused by the Sun is 50% less than the tidal force of the moon. Also moon phases affect tides. During the full and new moon, also referred to as spring tides, the tides are 20% larger and during first and third quarter moons, also referred to as neap tides, the tides are 20% smaller.

#### What are spring and neap tides?

During spring tides the tides are 20% bigger. Spring tides are when the sun, moon, and earth are lined up in a linear fashion. This causes higher high tides and lower low tides. This is because the sun and moon’s gravitational pulls are working to pull the water out higher in a higher high tide. Thus forming a lower low tide. Spring tides occur on new and full moons. During neap tides the tides are 20% smaller. Neap tides are when the sun, moon, and earth form a right angle. This causes higher low tides and lower high tides. Neap tides occur during the first and third quarter moon.

### Hypothesis

1. I predict that the tidal level in the Chesapeake Bay will be affected by moon phases.
2. I predict that the tidal level in the Chesapeake Bay will be affected by wind direction.

### Materials

• Internet (http://co-ops.nos.noaa.gov/)
• Computer
• Microsoft Excel 2000

### Procedure

Internet

1. Get onto the Internet and type http://co-ops.nos.noaa.gov/
2. Click on Water Level Observations
3. Go under Verified/Historical Water Level Data and click on U.S and Global Coastal Stations
4. Select Station: 8573364 Tolchester Beach, Chesapeake Bay, MD
5. Choose Time Interval: W3-Highs/Lows
6. Pick Datum: MLLW
7. Click Data Units: Meters
8. Type Begin Date: 20000701 & End Date 20000731
9. Select Output Format: yyyy/mm/dd hh:mm
10. Click Time Zone UTC
11. Click on View Data button
12. Repeat steps above replacing Step 8 with 20000801 & 20000831 for August, 20000901 & 20000930 for September, and 20001001 & 20001031 for October

Entering Data

1. Turn on computer and get into Microsoft Excel 2000
2. Create a spreadsheet titled "Tidal Level Data Table"
3. Title the first column "Date", the second column "Moon Phase", the third column "Wind Direction", and the fourth column "High TideLevel"
4. Enter all the data that was collected from the internet, into the spreadsheet
5. Then create a Scatter Plot graph comparing the moon phases and the high tide level
6. Make another Scatter Plot graph but this time compare the wind direction to the high tide level
7. Analyze data for patterns and trends
8. Write a conclusion