What if the natural ebb and flow of the sea along a beach shore was actually due to a larger planetary mechanism?
Well, you guessed it, it is. As we know, Gravity is a physically attractive force; this is how everything remains on the ground, not floating aimlessly like in space. Objects are drawn towards the center of Earth. Similarly, the Moon is constantly being held in orbit with the Earth due to the force of gravity created between them. Isaac Newton’s 3rd Law states that equal and opposite forces attract, ultimately summing up this large occurrence. The Moon has a stronger attraction to the Earth than any other planet or star, such as the Sun, because it is much closer. As a rule of thumb: the closer objects are, the stronger the gravitational attraction.
The Earth's rotation and the Moon's gravitational pull are the major Tidal Constituents responsible for tides on a planetary scale.
Figure 1: Diagram representing gravitational relationship of the Moon and Earth.
This relationship creates ocean bulges on both the side facing the Moon and the side facing directly away from the Moon as the Earth's water supply is redistributed. These bulges are our high tides. The bulge facing the Moon is understood to be a direct result of the tidal constituent of the Moon's gravitational pull pulling the ocean. However, the bulge on the opposite side suggests the whole planet is being pulled as well.
The relative top and bottom of the Earth, referencing Figure 1, are where low tides occur. As the Earth rotates, the low tide area moves into a high tide, and different parts of the world experience changing tides.
FUN FACT: Earth's land masses also experience movement everyday due to the Moon. These terrestrial tides cause land masses to move upwards of 55cm a day.
Spring Tides
The Sun, Moon, and Earth align approximately twice a month, creating especially high and then low tides, known as spring tides. These are most recognizable as the Full Moon and the New Moon. The gravitational pull of the Moon works with the gravitational pull of the Sun to create some of the highest and lowest tides depending on location and timing.
The period between spring tides is when neap tides occur- these are relatively weaker tides, and the Moon faces Earth at a right angle to the Sun.
How we See Tides
Most of the time, we know tides as being semidiurnal: tides that occur twice a day. This means that during the Earth's 24 hour rotation, different parts of the Earth and ocean experience different water levels depending on their current relation to the Moon. And thus we see the ebb and flow along the shoreline.
FUN FACT: Lakes and rivers also experience tides. The Qiantang River in China experiences the world's strongest tides and is therefore one of the biggest challenges for professional surfers.
Tides heavily depend on location as well; characteristics such as coastal features, depth, and expanse affect how the tide appears. Ecosystems heavily depend on the tidal characteristics of the area. For example, organisms living in high-tide zones need strong shells or safe hiding spots where they can cling to rocks; these animals include crabs, mussels, and barnacles. Tide pools form in mid-tide zones, and thus experience the most biological traffic. This area tends to have a large food supply and is a safe place for sea anemones, starfish, and many other softer organisms.
By: Madison DeLorme
For more information about tides, you can visit those referenced for this article:
“Tides – Moon: NASA Science.” Moon: NASA Science, moon.nasa.gov/resources/444/tides.
Cause and Effect: Tides. education.nationalgeographic.org/resource/cause-effect-tides.
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