Background Information for Teachers: What causes tides? Tides are the regular rise and fall of the waters of the ocean. Tides are caused by many forces, but the most important is the gravitational attraction of the moon. The next important force is the gravitational attraction of the sun. As the earth rotates, one of two bulges of water forms in the ocean on the part of the earth facing toward the moon. This tide is caused by the gravitational pull of the moon. This bulge moves westward around the earth as the earth rotates. At the same time, another bulge forms in the ocean on the part of the earth facing away from the moon. This other tide is caused by the weakness of the gravitational force that the moon exerts of that part of the earth. On the part of the earth away from the moon, the earth itself is pulled toward the moon more than the water is pulled (centrifugal force). This greater attraction on the solid part of the earth tends to create a bulge of water (a tide) on the side of the earth opposite the moon.
From the highest point on each of the two bulges, the water level slopes down ward to low points halfway between the two highest points. The low points result from the water being pulled away from those areas between the part of the earth facing the moon and the part facing away from the moon. The high points are high tides, while the low points are low tides.
Materials:
-Shoebox top
-tape
-pencil
-crayons
-circle of white paper with a 5 inch circumference
-rubber band
-string
-button or quarter
Narrative:
1. Ask students lead in questions such as: Have you ever been to the beach? Did you find a perfect spot to put your blanket, only to see that a little later in the day, the ocean seems to be closer than it was before? And later still, if you don't move your blanket, you'll be in the water? What's happening? What do we mean when we say the tide is coming in or going out?
2. Show the video "Tides"
What does the movie tell you about tides?
From the highest point on each of the two bulges, the water level slopes down ward to low points halfway between the two highest points. The low points result from the water being pulled away from those areas between the part of the earth facing the moon and the part facing away from the moon. The high points are high tides, while the low points are low tides.
Materials:
-Shoebox top
-tape
-pencil
-crayons
-circle of white paper with a 5 inch circumference
-rubber band
-string
-button or quarter
Narrative:
1. Ask students lead in questions such as: Have you ever been to the beach? Did you find a perfect spot to put your blanket, only to see that a little later in the day, the ocean seems to be closer than it was before? And later still, if you don't move your blanket, you'll be in the water? What's happening? What do we mean when we say the tide is coming in or going out?
2. Show the video "Tides"
What does the movie tell you about tides?
Assessment:
Ask students to brainstorm on what they think causes the tides. (Tides are caused by the gravitational pull between the Earth, Sun, and Moon. As the moon rotates around the earth the water follows it and causes the daily tides. The Sun's effect on the tides is about half of the Moon's because the Sun is so far from Earth).
Ask students to brainstorm on what they think causes the tides. (Tides are caused by the gravitational pull between the Earth, Sun, and Moon. As the moon rotates around the earth the water follows it and causes the daily tides. The Sun's effect on the tides is about half of the Moon's because the Sun is so far from Earth).
Small Group Activity: Make a model representing high and low tides
Procedure:
1. Color the circle to represent earth.
2. Push the pencil through the top of the shoebox top, near the far end (the pencil should stand vertically).
3. Paste the Earth circle about one inch in front of the pencil, on the top of the box.
4. Place the rubber band around the pencil.
5. Tie the center of the string around the middle of the rubber band at a point directly across from the pencil. Leave two equal lengths of string left t each end.
6. Place the quarter or button (to represent the moon) on the opposite end of the box top from the pencil.
7. Tape one end of the string to the center of the paper circle. Tape the other end of the string to the quarter.
8. Slowly pull on the quarter in a direction away from the pencil until the string attached to the rubber band is straight. Observe the shape of the rubber band as the quarter is tugged.
Results: The rubber band is pulled into an oval shape, with one pointed end towards the quarter, the other the pencil. How does this show how the gravitational pull of the moon affects Earth's tides?
Resources:
Have students finish filling out the "This is what I learned about the ocean" section of their foldable.
Procedure:
1. Color the circle to represent earth.
2. Push the pencil through the top of the shoebox top, near the far end (the pencil should stand vertically).
3. Paste the Earth circle about one inch in front of the pencil, on the top of the box.
4. Place the rubber band around the pencil.
5. Tie the center of the string around the middle of the rubber band at a point directly across from the pencil. Leave two equal lengths of string left t each end.
6. Place the quarter or button (to represent the moon) on the opposite end of the box top from the pencil.
7. Tape one end of the string to the center of the paper circle. Tape the other end of the string to the quarter.
8. Slowly pull on the quarter in a direction away from the pencil until the string attached to the rubber band is straight. Observe the shape of the rubber band as the quarter is tugged.
Results: The rubber band is pulled into an oval shape, with one pointed end towards the quarter, the other the pencil. How does this show how the gravitational pull of the moon affects Earth's tides?
Resources:
Have students finish filling out the "This is what I learned about the ocean" section of their foldable.
oceans_foldable.pdf | |
File Size: | 94 kb |
File Type: |
References:
http://teachersnetwork.org/teachnet-lab/ps101/bglasgold/lesson4tides.htm
http://www.youtube.com/watch?v=ASDmdl1HF5khttp://www.youtube.com/watch?v=ASDmdl1HF5k
http://teachersnetwork.org/teachnet-lab/ps101/bglasgold/lesson4tides.htm
http://www.youtube.com/watch?v=ASDmdl1HF5khttp://www.youtube.com/watch?v=ASDmdl1HF5k