Ocean Waves :

In general people think that ocean waves in deep water appear to be massive moving objects, like a ridge of water traveling across the sea's surface. However, an ocean wave is one of several kinds of waves, all of which are disturbances caused by the movemnet of energy from a source through some medium (solid, liquid or gas). The traveling hump, or ridge of energy, produces the appearence of movement we see in a wave. In an ocean wave, energy is moving at the speed of the wave, but water is not.

The nearly friction-free transfer of energy from water particle to water particle in the form of circlar paths, or orbits, transmits wave energy across the ocean's surface and causes the wave form to move. This kind of wave is known as an orbital wave, a wave in which particles of the medium move in closed circles as the wave passes. Orbital ocean waves occur at the boundary betwen air and water, or at the boundary between layers of water of different densities. Because the wave form in these waves moves forward they are known as progressive waves. - - - Hey man, get off my wave!

Ocean waves have distinct parts. The wave crest is the highest part of the wave which is above average water level. The wave trough is the valley between wave crests which are bellow average water level. Wave height is the vertical distance between a wave crest and the adjacennt troughs, while wave length is the horizontal distance between two troughs. The time it takes for two successive wave crests ( or troughs) to pass a fixed point, usually measured in seconds, is known as the wave period. Wave frequency is the number of waves passing a fixed point per second. Frequency is the inverse of period. (Refer to diagram )

Ocean waves are classified by the disturbing force that creates them, the restoring force that tries to flatten them, and their wavelength. The energy that causes ocean waves to form is called a disturbing force. Restoring force is the dominant force trying to return the water surface to flatness after a wave has formed in it. Wavelength is the direct measure of wave size.

Ocean Tides:

Tides are periodic short-term changes in the height of the ocean surface at a particular place caused by a combination of the gravitational force of the moon and sun and the motion of the Earth. With a length that can equal half the Earth's circumference, tides are the longest of all waves. These huge shallow-water waves are never free of the forces that cause them and so act in unusual but generally predictable ways. There are two bulges that form, one that is beneath the moon's position, and another bulge at a point on the Earth directly opposite of that position. The bulges are the crests of the planet-sized waves that cause high tides. Low tides correspond to the troughs. The wave crests and troughs that cause high and low tides are actually very small: A 2-meter rise or fall in sea level.

Tides come in many different forms:

Spring tides are the large tides caused by the linear alignment of the sun, Earth, and moon. They occur at two-week intervals corresponding to new and full moon.

Neap tides also alternate at two-week intervals. They occur when the Earth, moon, and sun form a right angle.

Tidal bore is a high, often breaking wave generated by a tide crest that advances rapidly up an estuary or river.

Tidal wave is a steep wave moving upstream generated by the action of the tide crest in the enclosed area of the river mouth.

Semidiurnal tides occur twice daily and consists of two low tides each lunar day.

Diurnal tides occur daily and consists of one high and one low.

Mixed tides occur when successive high tides or low tides are of significantly different heights through the cycle.

(These three types of tides above, semidiurnal, diurnal, and mixed tides occur at different locations on the Earth)

Extra Terms:

Amphidromic point is a "no-tide" point in the ocean around which the tide crest rotates through one tidal cycle.

Tidal datum is the reference level to which tidal height is compared. Tidal datum is "0" seen in tide graphs. This reference plane is not always set at mean sea level, the height of the ocean surface averaged over a few year's time. For the U.S. West Coast, tidal datum is mean lower low water, the average of the lower of the two low tides arriving on shore most day.

Tidal range is the high-water to low-water height differnce which varies with basin configuration.

To finish, to predict tides one can use the method of looking ahead at the position of the Earth, moon, and sun, and look back at the past History of Tides.