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TIDES

If possible, place sticks or other markers around the edge of a large body of water such as a very large lake, estuary, or ocean. Yeah, right. Put markers around the edge of, maybe, the Atlantic Ocean. Let's put sticks AT the edge of a lake or ocean.

After several hours check the markers in relation to the water's edge. Compare what you have observed with your previous seashore experiences. Sand castles, or love letters in the sand, may have been washed away as the water levels have risen.

The natural rise and fall of water levels in a large body of water is called a tide. You might be interested in looking up information about tides in the daily newspaper, almanacs, or tide books available at sporting goods stores.

Here's another one:

Draw a 20 inch diameter circle on a chart or chalk-board. The circle represents the earth. Imagine that you are above the North Pole looking down upon the earth. Now draw a 5 inch diameter circle 4 feet away from the "earth" to represent the moon.

The earth and moon attract each other. The moon's attraction causes the ocean to bulge directly outward toward the moon, and there is another bulge on the opposite side of the earth.

Draw the bulges, and letter the high and low positions of the ocean. There are several numerals on the earth. Describe the various tides from those positions as the earth turns. For example, you might say that from position 1, the tide seems to be coming in or rising (because the earth is moving into the bulge) and that from position 4, the tide seems to be going out.

You should be able to tell that there are 12 hours between one high tide and the next high tide and 6 hours between changes in tides.

Your brilliant writer knows very well how much time there is between tides. During low tide at Cannon Beach, Oregon, when I was about 12 years old, I was checking the stuff at the base of the a large formation called "Haystack Rock." I was very fascinated by the starfish on the ocean side of the rock. I climbed up onto the rock so I could take some photos from a few feet above the tide pool where the starfish were. Next thing I knew, the water was swirling around the rock, and the way it was swirling, it was not safe to try to swim back to the beach. So I sat on the rock for what seemed to be an eternity, until the tide went out again.

Here's another one:

Use models of the sun, moon, and earth to show that:

1) when the sun and moon are in line, their gravitational influences combine to produce the highest possible tides (spring tides);

2) when they are at right angles to each other, their
influences divide and produce lower tides (neap tides).

This looks like fun, but I don't know what it will teach us.

Try to carry a shallow pan of water across the room without spilling any water. (This will be very difficult to do.)

(I got it. It will teach us to clean the floor!)

The sloshing motion is similar to the motion set up in great ocean basins around the world (e.g., the Bay of Fundy).

So where is the Bay of Fundy? It is a "large inlet of the Atlantic Ocean, about 170 miles long and 30 to 50 miles wide, in North East Canada, between New Brunswick and Nova Scotia. It is famous for its tidal bore and for high tides that reach 40 to 50 feet, creating the reversing falls of the St. John River.

Tide is defined by the Concise Columbia Encyclopedia, is the "alternate rise and fall of sea level in oceans and other large bodies of water. These changes are caused by the gravitational attraction of the moon and, to a lesser extent, of the sun for the earth. At any one time there are two high tides on the earth, the direct tide on the side facing the moon, and the indirect tide on the opposite side. It is believed that the indirect tide is caused by the moon actually pulling the earth away from the water on the far side. The average interval between high tides is about 12 hours and 25 minutes. The typical tidal range, or difference
in sea level between high and low tides, in the open ocean is about two feet, but it is much greater near the coasts. The world's widest tidal range occurs in the Bay of Fundy in East Canada. Tides are also raised in the earth's solid crust and atmosphere."

The encyclopedia has a more sophisticated discussion of Tides and Their Causes, a copy of which, if you want to be thorough, you will request from your teacher.

 
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