Waves and Tides

The word "tides" is a term used to define the alternating rise and fall in sea level with respect to the land, produced by the gravitational attraction of the moon and the sun. To a much smaller extent, tides also occur in large lakes, the atmosphere, and within the solid crust of the earth, by the same gravitational forces of the moon and sun. Tides are the periodic rise and falling of large bodies of water. The moon is important to us because it creates tides. Tides are daily movements of ocean water that change the level of the ocean's surface.The tides are caused by the exertion of gravitational forces by the moon and sun, and the rotation of the Earth. The relationship between the phases of the moon and the tides was first discovered more than 2,000 years ago by Pytheas, a Greek explorer. However, Pytheas could not explain the reasons behind the relationship. It was not until Sir Isaac Newton published his theories on gravitational pull in 1687 that the relationship between the moon and tides were fully understood. Gravitational forces from both the sun and moon continuously pull on the Earth. It is the moon's gravity that is the force behind the Earth's tides. Every particle on Earth is pulled on by the gravity of the moon. Because liquids move more easily, the pull of gravity is much more noticeable in liquids than in solids.

The moon's pull is strongest on the part of the Earth directly facing the moon. When that part of the Earth happens to include an ocean, the water there bulges toward the moon. Water on the opposite side of the Earth bulges due to inertia caused by the motion of the Earth and moon around each other. The bulges is called high tides. The figure below shows the position of the moon that causes the water to bulge. Notice that when high tides occur, water is drawn away from the area between the high tides, causing low tides. Two high tides