How Tides Work?

01.04.2015 |

Episode #10 of the course “Science questions everyone should know how to answer”

French astronomer François Arago once said that studying the tides was the tomb of human curiosity. We promise this explanation won’t kill you, but Arago was right that the science of tides is very complex. A lot of different factors go into the ebb and flow of the ocean, but the big three are the moon, the sun, and the earth. In short, the gravitational force of all three of those interacting with each other creates the tides.

The moon is the biggest factor. Even though the earth is bigger than the moon and therefore exerts more of a gravitational pull, the moon still has gravity of its own, which it exerts on the earth. The moon’s gravity doesn’t affect us, or buildings, or other solid things on earth, but it does affect the water. Water is fluid and thus more susceptible to gravity, so the easiest explanation of tides is that water rises towards the side of the earth that the moon is currently on because the moon is using its gravity to pull it that way.

However, the earth itself is also being pulled towards the moon ever so slightly, which creates another high tide at the exact opposite end of the moon. Water is finite, so as the moon pulls water towards one end and the earth moving towards the moon creates high tides on the opposite end, the two sides are being deprived of water. Thus, if you picture the moon on the top of the earth in a two-dimensional view, the top and bottom of the Earth will have high tides while the two sides will be in low tide.

The sun plays a role as well, albeit a lesser one than the moon. We have what are called spring tides, when the moon and sun are in alignment. Since the sun is so massive, it enhances the gravitational pull in the direction of the moon. Conversely, when the moon is at a 45-degree angle from the sun, its gravitational pull is diminished. These are called neap tides.


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