By: Courtney Thomas Lauren Goldfinger Kelsey Tamburri Sara Kielbasa

 Ocean tides are the cycle of the rising and falling level of seawater.  They are one of the most reliable phenomena this world has to offer.  There are now even charts that show when high and low tide will be each day

 Tides are actually waves that have very long periods and move through the ocean. Tides will start in the ocean and work their way in towards the coast lines.  When the crest, or highest part of the of the waves reaches the coast it is high tide, and when the trough of lowest part of the wave reaches the coast it is low tide. BUT the real question is HOW DO THEY WORK????

What is it that causes tides to happen? GRAVITY! The gravitational force between the earth and the moon, and the earth and the sun causes the tides.

The moon has more of an effect on ocean tides than the sun. The sun is actually half as effective as the moon at causing tides even though its pull on the earth is 180 times greater. So why is this? This is because the of the great distance between the Earth and the Sun!

The moon creates two bulges on opposite sides of the earth that create high tides. Because the force of gravity is greater when the distance is smaller, the gravitational force between the Moon and Earth is stronger of the side of the earth closer to the moon. One the opposite side the force of gravity is much smaller because the distance is much greater. The lack of a strong pull makes this water bulge away. On the two sides perpendicular to the bulges is where the low tide will occur.

The picture summarizes what we have talked about so far. Both the sun and moon have a gravitational pull on the earth, however, the sun's is much smaller. The side of the earth that is nearest the moon, and opposite the moon have the bulge, which is high tide. The sides perpendicular to those are pulled in towards the earth because they have little pull, which creates low tides.

Why is it that there are two high tides and two low tides a day??? The reason there are two high tides and two low tides everyday are because the earth rotates! It rotates one time every 24 hours. Because of this rotation, one spot on the earth will be closest to the moon, creating a high tide. 12 hours later that same spot will then by opposite to where it was, farthest from the moon, which creates another high tide. In the middle of the 12 hour intervals the spot will be at one of the spots of low tide. Hence why about every 6 hours there will be either a high or low tide, and why there are two cycles of tides per day.

Why do the times of high and low tide change everyday??? Throughout the day the Earth rotates 360 degrees in 24 hours, so that means it rotates 180 degrees in 12 hours. The Moon is also rotating though. The moon rotates 6 degrees around the earth every 12 hours, or 12 degrees in one day. This makes it so that a high tide occurs once every 12 hours and 25 minutes. So, the two-high-tide cycle is actually 25 hours and 50 minutes. This makes it so that high and low tide are not the same time everyday.

If the sun’s gravitational pull is less then the moon’s then when does it actually effect the tides???? Sun tides are only about half as high as lunar, or moon tides are. The main times that the sun plays a noticeable role in tides is during neap and spring tides.

At certain periods throughout the cycle of the moon, the moon, sun, and earth all align. This happens during full and new moons, which is about every days. When this happens it creates more extreme tides, so higher high tides, and lower low tides.

When the gravitational pulls of the sun and moon are perpendicular to each other, it creates neap tides. This is when the moon is halfway between and new and full moon. When this happens it creates less extreme tides. So lower high tides, and higher low tides.

Tides are not as cut and dry as they seem. There are over 400 variables that affect the times, size, and number of times at any one place or latitude!!! Some other variables that affect tides are: The tilt of the earth The geometric location of the moon and sun to a place

Even though the bulges are considered equal the earth’s tilt causes the high and low tides in most places to actually be unequal

The geometric relationship of the moon and sun to a place causes three types of tides: Diurnal: one high and one low tide per day Semi-Diurnal: two high and two low tides per day Mixed: the high tide and low tides differ. These various types of tides happen in different areas of the world

The text book: “Conceptual Physics” by Paul G Hewitt physics/tide-cause.htm tml