Moon’s gravity doesn’t explain everything about the tides


Although at school teachers teach us that tides exist due to the influence of the Moon’s gravity on Earth, the truth is a bit more complex. According to what we have learned, as the distance and approach of the moon varies, there is also a variation of the tides, but this does not imply that the moon is pulling or compressing the tides, if this was the reality, we would also see it happen in lakes and dams, or even in the pools of our houses.

If we do a search for videos on the subject on the Internet, we will come across various sources, some credible and some less, to explain incorrectly the physics of the tides, following the general and imprecise basis of what was transmitted to us at school.

In fact, throughout the circumference of our planet, although gravity may suffer slight variations, it is in general about 10 million times stronger than the moon’s gravitational force. In fact, tidal variation is the result of a complex variation of gravity between the Moon, the Earth and the Sun, compressing and drawing water from the Earth, and although all water is actually attracted due to the Moon’s gravity, the effect is not observable at the molecular level since the gravitational pull of the Earth is superior.

The reason ocean water is affected by this force comes from an old credo, “unity is strength,” and since ocean water covers about 71 percent of the Earth’s surface, it acts as a single body, and so every single molecule of water affected, in union with the next molecule and so on, creates the effect of the tides.

Since the water molecules of the planet’s poles are mostly drawn to the planet’s core, and with the molecules on the equator line being more attracted to the moon, the planet’s most distant molecules suffer a lower gravitational acceleration, and since molecules of water are able to collide with each other without great effort, the group effect decreases the concentration of water at the poles, by concentrating water on the equator, and as the planet rotates, we experience the phenomenon of tides, that is, every 6 hours.

Lakes and dams are not affected by tides because their water bodies are too small for them to take effect.

Below you can see a video by PBS Space Time, where Gabe Perez-Giz explains with more detail the phenomenon.

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