Published on June 9th, 2011 | by Yellow Magpie1
Tides: Forces We Take For Granted
Tides are caused by a complex interaction between water, wind, gravity, surface tension, earthquakes and the Moon.
One of the most fundamental forces on Earth, tides particular the tides caused by the Moon have been responsible for the creation of life on our planet. Yet it was until only recently that a clear understanding as to how they work has been formed.
The frequency of tides means that they have a great effect upon humanity and life on Earth. This is particularly true of people who live near the coastal areas and fishermen but it affects virtually all of us. The vast majority of goods in the 21st century are transported via ship. Tides are the increases and decreases in the height of our oceans and seas caused by Earth’s rotation, the Moon and the Sun. But at a more basic level they are the longest waves.
What Are Waves?
We often look at water rippling across ponds or waves crashing into coastlines. Waves are ubiquitous. There can be sound waves, light-waves or radio waves amongst others. Ultimately, waves are simply energy.
Waves of water are no different. The water itself does not really move, although there is a slight displacement which corrects itself. Rather the pattern of the wave is what moves – the water stays in the same position.
Water waves are a type of surface wave. Surface waves are waves that pass through two different mediums. In Earth’s case these two mediums are water and the atmosphere.
As the waves move – forces restore the water back into its original position. Two different forces are responsible for returning the water to its previous state -which one is dependant upon the size of the waves. If the wave is less than 1.7 cm (less than one inch) surface tension is the agent. While if the wave is greater than 1.7 centimetres – gravity brings the water back to rest.
Daily Tides And The Moon
The daily ebb and flow of the tide is caused by the Moon’s gravitational pull on Earth. This process is cumbersomely named the Principal Lunar Semidiurnal Constituent. These tides are caused by the Moon’s gravity causing the water to bulge on the nearside of the Earth.
However, the Moon also causes a swell of water on the far side of the planet as well because sphere when pulled on side form ellipses. This is what happens with water on the Earth and what results are the high tides.
In between the two bulges are the areas of low tide. It takes a little over 12 hours for each high tide to occur and of course the same 12 hours between low tides.
Neaps And Spring Tides
The role of the Sun and the Moon becomes more evident in the cases of the twice-monthly neap and spring tides. Spring tides are caused by the Sun, Moon and Earth aligning into a straight line. This happens when the Moon is at either the full or new phase of its month cycle. Spring tides are much higher tides than normal.
Neap tides are the exact opposite. Instead of the forces of the Moon and the Sun both acting on the Earth they cancel each other out. This happens when the Sun and Moon create a right angle with the Earth. Neap tides occur twice a month when the Moon is in its first and third quarter phases. Water levels on Earth are at their lowest during neap tide.
The Big High Tides
Occasionally, every seven to eight months, or so, there is a high tide that exceeds the normal spring tide. This is caused by the Moon being in perigee. That is when it is closest to the Earth. This type of tide is called a perigean spring tide.
The tides play a vital role for navigation. Constant attention must be paid to them as they dictate when ships can enter and leave ports. Animals and plants also rely upon knowing the layouts of the tides. The tide process has directed many systems on Earth over millions of years and it will continue to do so for the conceivable future.
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You can obtain Waves, Tides and Shallow-Water Processes here from Amazon.
For people living in Ireland or the United Kingdom you can access Waves, Tides and Shallow-Water Processes (Oceanography) here.
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For Germany: Waves, Tides and Shallow-water Processes.
For France: Waves, Tides and Shallow-Water Processes.