# Why does water get effected by gravity by the moon but not us as humans not as much?

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Why does water get effected by gravity by the moon but not us as humans not as much?

In: Earth Science

It’s not a matter of water vs humans.

It’s a matter of weight (mass to be correct). Gravitational force is proportional to both masses involved, as well as the distance between the two masses.

A lake or ocean has a HUGE mass. Therefore it can get greatly affected by gravity.

A human in comparison has a much smaller mass. If you do the math, the gravitational force of the Moon on a human is MUCH weaker than the gravitational force of the Earth (which is much closer) on the same human.

Assuming you mean tides, it’s like a swing, over 100s of millions of years the tiny tug this way, and then that way, has added up to huge masses of water moving across oceans.

Smaller bodies of water like lakes just don’t have the room for the swing to create the effect. And human bodies move around on their own making the effect irrelevant.

The force of gravity is inversely proportional to the distance squared between the object (g~1/r²) so if there is only a small change in the distance gravity barely changes at all, but if the change in distance is large – say opposite sides of Earth – there is a significant difference. This difference in attraction of water towards the moon on opposite sides of Earth is what causes the tides – anything as small as a human simply does not experience such a gravity differential.

Edit: Well, the changing of tides is the result of Earth spinning faster on its axis than the Moon is orbiting it, meaning the bulges of water on both sides of Earth inline with the Moon due to the gravity differential change position relative to Earth’s surface.

Yes, we do. If you are on a boat your position relative to the center of the Earth will vary. If you are on ground your position won’t change, at least not in a perceptible way. The difference is that in the boat there’s trilions of particles of water each pushing in an imperceptible way towards the Moon.

Something that makes this easier to understand

The moon only creates waves because the oceans are so big. The moon can only pull each water droplet a tiny bit, but it pulls on many of them at once, and it builds into a wave over miles and miles of open water.

It can only make a wave because it can get a running start, essentially. Otherwise it isn’t pulling very hard.