Tides Spring and Neap

Tuesday, October 1, 2019

What causes tides?

Tides are the rise and fall of sea levels caused by three items.

The gravitational force of the Moon
The gravitational force of the Sun 
The rotation of the Earth 

So let’s take a look and see how these three items cause tides.


Gravity is the force of attraction between two objects. Anything that has mass also has gravity. Objects with more mass have more gravity compared to objects with less mass. Gravity also gets weaker with distance. The closer objects are to each other, the stronger their gravitational pull is.  Although the moon is much smaller than the Sun the moon's gravity has a much more pronounced effect on the Earth's ocean because it is closer than the Sun. 
On the side of the earth that's facing the moon, the pull of gravity causes oceans to bulge outward due to the gravitational pull of the moon.
 On the other side of the earth away from the moon, the gravitational attraction of the moon is less because it is farther away. Here, inertia exceeds the gravitational force, and the water tries to keep going in a straight line, moving away from the Earth due to centrifugal force, also forming a bulge.

The Earth rotates on its axis so this bulge, which is called the tidal bulge, is constantly changing location. The tidal bulge changes as the moon revolve around the earth.  Where the Bulge is bigger it's high tide, and where the bulge is smallest, it's low tide.

 The tidal range is the height difference between high tide and low tide. The world's largest tidal range of 16.3 meters and occurs in the Bay of Fundy, in Canada.
Most places get two high tides and two low tides each day. If you are on the part of the Earth-facing the moon you are at high tide, 6 hours later you will be at low tide, 6 hours later you will be back at high tide, and then 6 hours later you are back at low tide, and finally, after 6 more hours, you are back at high tide.

 Approximately twice a month around the new moon and full moon when the Sun Moon and Earth form a line the tidal force is at
its maximum and the tidal range is at its maximum this is called spring tides. 
When the moon is at first quarter or third quarter the Sun and Moon are separated by 90 degrees and the solar tidal force cancels the moon's tidal force and the tidal range is at its minimum and these tides are called neap tides.

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