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The height of water changes each time I go to the beach.  Why? 

The tide is the movement of the ocean. Currents and the tide are not the same thing, currents are a horizontal movement and the tide is a vertical movement.  There are two movements which is are called ebb tide, when water goes out, and flood tide, when water comes in.  There is also spring tide, which is when there is much change in the tide and neap tide, when the tide almost has no change.  It takes six hours for the tide to change from ebb to flood or flood to ebb.  The tide changes each day, but it can be approximately the same one for one week.  The tide is different in each location, for example, in the Bay of Fundy the maximum flood is 8m (which is called a proxigean tide), but in Victoria, it is only 3m.  Around the islands in the middle of the ocean, the change of tide is very small.  On the beaches in Hawaii, the maximum flood is 0.45m and the maximum ebb is -0.5.  Why?  In the middle of the ocean, all the tides of the continents will join which stops movement of the tide completely.

 I know that the tide is the movement of the ocean but why be-that there is movement? 

The biggest causes are the moon and the sun.   The water always goes in the direction of the moon because of lunar gravity.  Also, the moon and the earth turn together which causes water to rise on the opposite side of the earth than the moon, which causes a flood tide on each side of the earth.  The water also rises in the direction of the sun.  That is also caused by gravity, but, the gravity of the sun is only 0.033 that of the moon because the sun is much further from the earth that the moon.  The movement of the earth, the moon and sun effect much the tide, if the moon and the sun are on same side of the earth, they will work together and will make the tide flood on their side of the earth and ebb on the other.  But, if the moon makes a half turn of the earth towards the sun, the tide will go up in all the directions.  The earth turns on its axis, therefore, the moon will face all the continents on the planet in one day.

The tide does not remain the same pattern.  Why? 

First of all, a factor is what creates the changes of the tides.  One factor of the tide is the weather.  For example, if there is wind, the tide will move more quickly.  Another factor is the earth on a beach.  If the beach is big and flat, you can see much change in tide, but if the beach is narrow is steep, you can’t see as much change.  The tide can also change with surfaces on the bottom of the ocean.  For example, if the ocean floor has lots of friction (like if there was rocks), the water will move more slowly, but, if there is not much friction (like if there was sand), the water will move more quickly.  The tide is like a big wave that turns travels around the earth, and the continents are like obstacles.  So, when the wave goes between continents, it will travel back and forth. 

If there are marine animals that live in the area where the water rises and descends, will they die when there’s a low tide?

No.  There are many species of animals that live in the tides.  The majority of these animals are not fragile and they can live in the air and water.  The tide causes an ecosystem which names the intertidal zone.  There are three different sections in the intertidal zone; the high section, the middle section, and the low section.  The high section is only covered with water during a flood tide.  The species which live in this section need more air than water.  The middle section is covered with water regularily.  The kinds of species which live here need as much water as they need air.  The low section is only dry during an ebb tide.  The kinds of species here need more water than air.

How do we know the tide in advance?

Now, we don’t need to predict the tide, thanks to machines and technology.  Tide predicting machines were invented in 1873 and to improved by Mr. William Ferrel.  The simple prediction it is that the tide changes from flood to ebb or ebb to flood every 6 heurs, then, if the moon is above or below the earth, there will be a flood tide and if the moon is on the horizon, there will be an ebb tide.  But, to have a more precise prediction, you need know movement of the planets (the earth, the moon and the sun), factors of the tide and when the big wave which turns around the earth is relented.  The wave is relented approximately six hours per day.  A source of error for the simple prediction is that the earth takes one day to make a rotation, but, the moon takes 28 days, so when the earth is finished a turn, the moon has moved 1/28 of its turn, so, the earth needs to turn more to catch up to the moon.  The earth takes 51 minutes has to catch up to the moon.  So, the earth needs to turn 1/28 of 24 hours.  1/28 of 24 hours is 51 minutes.  If it takes 51 minutes for 24 hours, that means that it takes 25.5 minutes for 12 hours, so, there is 25.5 minutes between each flood tide and ebb tide.