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How is it that the moon can affect the 352 quintillion gallons of water in the ocean, but not affect us?

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1289 utenti della rete avevano questa curiosità: Spiegami How is it that the moon can affect the 352 quintillion gallons of water in the ocean, but not affect us?

The moon depending on where it is at your time of day can affect whether or not there's high or low tides. Basically moving all of the water in the ocean, at least that's how I think. But how come it doesn't make us feel lighter or heavier throughout the day? Or just seem to affect anything else

Ed ecco le risposte:

It does effect us, just very, very minorly. Gravity tends to be more noticeable on objects with a lot of mass. The ocean, being both very very massive along with fluidity, makes gravity very noticeable on it.

When the moon is directly above you as opposed to directly under, you will weigh a very very marginally lighter.


So instead of thinking the whole ocean is being pulled by the moon, Think of it instead that there is always a bulge of water facing the moon, There is also another bulge of water facing the opposite side of the earth too.

We will call these bulges ‘high tide’.

The earth is actually spinning through these bulges of water and as we reach a bulge the ocean gets this extra bulge of water and we experience a high tide.

Once we spin out of the bulge past the moon the water drops again and we experience no bulge which is ‘low tide’.

The rhythm of us passing through these bulges of water each day is the tides.

The bulge is always there being pulled up towards the moon, We just slide through it.

You also get extra bulges from the sun, but these are usually smaller.

Here is a helpful NASA visualisation

The tides usually only change the sea level by a metre or so. Compared to the full depth of the ocean and the mass of water it contains, that’s a really negligible amount. You’re also experiencing the effects, but would you notice a 0.01% (example not the actual figure) change in your weight? A tiny tiny change in something the size of the ocean becomes noticeable to us because we’re so small in comparison.

You’re not large enough to feel the effects of the moon. You’re a small, mostly liquid, packet of water-like substance.

Since this is an Spiegami: When standing directly under the moon (perpendicular to the earth), you will weigh some amount less. Let’s say 0.0001% less. Now, for someone who weighs about 60kg, that’s about 60 milligrams. So you weigh 59.99994kg instead of 60kg. You won’t notice this. Your body isn’t large enough to notice any bend.

Now place a a 10kg bucket of water on the ground. When the moon is overhead, it also will weigh 0.0001% less. It’ll weigh 9.9999kg. You won’t see a bulge in the water, because it’s too small for you to notice such a small difference.

The pacific ocean has about 6*10^20 (600,000,000,000,000,000,000) kilograms of water as an estimate. It also will weigh 0.0001% less. When the moon is overhead, it will weigh about 5,999,400,000,000,000,000,000kg. Notice, the ocean will now weigh 600,000,000,000,000,000Kg LESS. That’s how much lighter the pacific ocean will be. This difference in weight will be noticeable over large distances.

Also, for a distance of thousands of miles, the ocean will rise just a few feet. That’s not that much higher when you take the whole ocean into account.

If you had a small bucket of water, and measured down to picometers the water level when the moon was overhead vs not overhead, you will probably measure some tiny difference!

We’re too small. It does affect us, but to no noticeable degree.

Earth is close to us. It pulls very heavily on everything on it. Including all the water on it. This creates a LOT of pressure as the weight of water piles onto itself in the deepest parts of the sea.

The moon pulls very slightly on everything on earth. The further it is from us, the less it pulls. So, if the moon is close, everything on earth isn’t being pulled as heavily from the Earth’s gravity, since a tiny bit of that force is alleviated.

We can’t notice that change. But, in the deepest parts of the ocean, a little bit of change in force is enough to alleviate some of the pressure built up from the water on top of it. On the other side of the planet, water is still being pulled by the moon, compressing it down, creating pressure which will be alleviated when the orbit swings back around.

All the pressure differences across the planet end up creating low and high tides, which as others have described, can be thought of as a “bulge” of water that faces the moon.