AIM: What are tides?
1. Ask children 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 "Seashore" by Eyewitness Video. What does the movie tell you about tides?
3. Show students the following pictures. Which picture shows low tide? Which picture shows high tide? (Pictures were created and imported on KidPix).
1. Introduce vocabulary: tide, spring tide, neap tide, low tide, high tide, moon, phases, gravitational pull, heavenly bodies, and mass. Children are to look up the words from http://m-w.com.
2. 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). Look at the animated figure at the following link: http://science.nasa.gov/headlines/images/missingtides/dissipation.gif
What are Spring (Leap) tides and Neap tides? Have children go to http://geog.ouc.bc.ca/physgeog/contents/8r.html
and study the two diagrams illustrating Spring and Neap tides. Children
are to label which diagram shows Spring tide and which diagram shows Neap
tide. (The following pictures are taken from the above site)
1. Make a model representing high and low tides. (This activity is an abridged version of the one found in Oceans For Every Kid, by Janice VanCleave, John Wiley and Sons, Inc., 1996)
Depending on the maturity of the students, this can either be a teacher demonstrated lesson or small group activity.
Materials: Shoebox top, tape, pencil, crayons, circle of white paper with a 5 inch circumference, rubber band, string, button or quarter.
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?
Have children answer the following questions:
a. When are the two times a month that we have Spring tides? Why? Explain in paragraph format. (When there is a full moon and new moon because the sun and moon are in line).
b. When are the two times a month that we have Neap tides? Why? Explain in paragraph format. (When there is first quarter and last quarter because the moon and sun are on opposite sides of the earth and their pull cancels each other out)
c. Why doesn't the sun affect the tides as much as the moon does? (Because the sun is much further away).
d. Why is it more dangerous to have a hurricane during a Spring tide? (Because spring tides are higher than normal, and hurricanes raise the height of tides due to the increased rainfall and winds).
2. What time are low tides and high tides at Coney Island?
a Have children go to http://fishingworks.com/ and use the Tide Predictor to find the times for low tide and high tide at Coney Island. (If Coney Island is not available, any New York beach will do).
This lesson will lead into the next lesson "What
are ocean currents?"