Why does the moon have gravitational power to create tides, but not to lift any other objects?

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If the moon creates the tides, why don’t any other objects get lifted by its gravitational pull?

In: Planetary Science

22 Answers

Anonymous 0 Comments

It’s because the oceans are freer to move.

Your premise is correct in that every gram of matter near to sea level experiences the same gravitational force, be it water or dirt or air – the gravitational force is primarily made up of the moon’s pull and the earth’s pull (the sun also contributes nontrivially but we can ignore for the purpose of this answer).

Given that, if gravity were the only force and all matter is free to move, we’d expect the earth to be roughly shaped like an ellipsoid pointed in the direction of the moon – the closer points experience more pull and the farther points less.

However the other matter on the planet are less able to move. Land is mostly solid and harder to deform. There’s more forces holding land together. So for the most part we think of the landmass on earth as a solid shape moving through the bulging water mass.

For an ELI5 visualization, think of spinning a water balloon at high speed vs spinning a bowling ball at high speed. The water balloon is more ready to deform and thus follow the direction of the centrifugal spin. The bowling ball has the same tendency but is held back internally by molecular forces.

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