When people go to the ocean they almost always look for shells on the beach. The best time to look for them is in the morning. Did you ever wonder where they came from since they weren't there the night before? About every twelve hours the tides rise and fall, sweeping the bottom of the ocean as they go along. It might be hard to believe, but the ocean's tides have timetables on the Internet just like trains and airplanes. These tides are always changing because they are affected by the rotation of the earth and the moon. The moon affects many things here on Earth. Scientistslike to keep an eye on the patterns and changes so they can predict what they call high tides. Why, you ask? In some places, like the Bay of Fundy off the easterncoast of Canada, the tides can change the level of the water around fifty feet; you wouldn't want to be standing on the beach with all that water rushingtoward you! You may be wondering what has the strength to raise all that water on both sides of the earth? Although the sun's gravity has some effect, it is the gravity of the moon, even though it is hundreds of thousands of miles away, that exerts so much pull on the earth's surface. Over time, the moon's gravity has even slowed down the speed of the earth's rotation! You might also be wondering if the earth is doing the same thing to the moon? Over the years, the earth's gravity has slowed the moon's rotation so much that it now turns at the same speed as it orbits the Earth causing us to see only one side of the moon.