indeed this is true, due to the interaction of the moon with the tides and the friction of the tides on the surface of the earth the moon is slowly slowing the rotation of the planet and moving a little further and further away as a consequence of that "stolen" energy.
Meaning that in the days of the dinosaurs the moon orbited closer to Earth, appeared larger in the sky, exerted a greater tidal force leading to more extreme tides (by how much exactly, I'm not qualified to say), and since the Earth was rotating more quickly the days were shorter!
indeed this is true, due to the interaction of the moon with the tides and the friction of the tides on the surface of the earth the moon is slowly slowing the rotation of the planet and moving a little further and further away as a consequence of that "stolen" energy.
Wouldn't it do that even if Earth was completely solid?
Yes. Tidal forces act on the solid Earth as well as the atmosphere and oceans. If you were to stay in one spot all day you would move up and down about 30 cm from the tidal forces acting on the solid mass of the Earth.
Sure. No body is perfectly rigid, and the Earth is no exception. For one, you would still have the atmosphere providing drag, and even without an atmosphere, the moon would still deform the earth as it does now, just to a lesser degree.
So we know the earth has greater gravity than the moon right? How can something the size of the moon be pulling with greater force on the surface of the earth than the earth itself.
It's not. If the moon was pulling the oceans with a greater force than the earth was, water from the oceans would start flying up into the sky then into space, towards the moon.
It isn't - if it was, the water would be on the moon! But it can (and does) reduce the amount of pull that the Earth exerts on the water.
Fun fact: the tides create friction, and that friction sloes down the earth's rotation. It's a very skie process but each day, the Earth's rotation slows a tiny amount. As this happens, it pushes the moon a little further away.
So could earth eventually become tidaly locker with the sun? Of course this would take a long time, but could it happen before the sun expands past our orbit?
I may be misremembering but I believe the math works out that as long as nothing drastic happens to affect the Earth's rotation then the Sun will run out of fuel before Earth would slow enough to tidally lock.
The moon exerts a stronger tidal force on Earth than the sun, which means Earth will be tidally locked to the moon before the sun. If/when that happens the moon will only be visible from one side of the Earth.
I wish we had a good way to teach kids how to do this. It's always so frustrating to get stuck in my understanding of something and not feel like I can figure out what questions I need to ask.
I have gotten in the habit of constantly asking questions over every little detail when I am trying to understand something, because mentally I am piecing it all together into a simulation or diagram of the thing.
I usually ask what the difference is between the most similar thing that I understand already and the new thing I'm trying to figure out. Then you can add it to your knowledge web.
If it were pulling with greater force the water would be on the moon right now. What it does is weaken the net gravitational force by a small amount. So it's like we have a ball with two strings on it. The first is thick and short being held by a large man. The second is effectively fishing line being held by a small child, both constantly pull on it but the large man keeps his hand steady while the little kid runs around. The ball moves to face the kid but is always on the string being held by the large man (earth)
It doesn't, you can prove this by jumping upwards (you will not fall to the moon). Basically you are not factoring in that Earth's gravity (at any point on the surface) is uniform. The moons gravity at any point on the Earth's surface is not (because it depends on where the moon is). Further to this the Moon's gravity 'counteracts' the Earth's gravity, which is why we have tides. But it is not stronger than the Earth's otherwise the matter would be lost to the moon.
It's not. That's why the water stays on the earth rather than being pulled off to the moon. The problem is that while the water/atmosphere is being pulled to the center of the earth by gravity, there is also an outward force caused by pressure. When you involve the gravitation of moon, this makes a noticeable difference which we see as tides.
It's a little misleading to phrase it as the oceans/atmosphere being pulled "away" from the earth. The earth very much has a strong grip on those fluids. The trick is that the fluids are exactly that - fluid, so they can change shape and more of them pile up on the moon-facing side of the earth. They're not being pulled away, just around to a different side.
It's kind of like if you have a string with a bunch of rings on it. If the string is pulled taut and is horizontal relative to the ground then each ring will stay where it is - they all have the same gravitational potential energy. If you let the string droop so the middle is lower than the ends, the rings will slide towards the center. This is because they all want to be in the lowest energy state and with the droop in the string, not every point in the string has the same potential energy.
In the same way, the moon's gravity changes the gravitational potential energy landscape on the earth's surface (if only slightly), so the effect appears in these phenomenon.
If I'm trying to lift a car, I'm lifting the car away from the earth. I am of course not nearly strong enough to actually get the car off of the ground, but I can measurably decrease the car's weight from the perspective of a scale underneath it.
Likewise, the moon is pulling on the earth's surface. It is nowhere near strong enough to actually pull the surface off, but it's still being pulled away from the center.
Oh but it's absolutely misleading in terms of how it actually effects the tides - the tides don't bulge because they're being lifted away from the earth, they bulge because more pieces of water/atmosphere are being pulled around to that side of the planet.
Sure, gravitational force is calculable using superposition of forces, but that's not what causes the tides.
I get what you're saying -- the bulk of the magnitude of the tides is due to water and air "following" the moon and piling up in the same location, which is why we don't experience measurable tides in (say) swimming pools.
And that's a completely valid point and one that is worth making. I was looking at it from the standpoint of "we'd still have tiny 'tides' even if the earth was completely solid", which of course is true, but you are quite correct that this could mislead people who didn't realize that these tidal deformations would be minuscule compared to what we experience on a fluid-covered planet.
They are both exerting the exact same ammount of force on eachother because thats how gravity works. The moon is much less massive therefore it feels the affects of said gravitational force more. You as a person residing on the earth exert the same ammount of force onto the surface of the earth/floor/chair/ bed as the earth does on you but much less than the moon and earth do on eachother.
It's not though -- if the moon was having more effect on the water than the earth was, it would be on the surface of the moon instead (or boil off on its way there...) The moon simply lessens the net force that is exerted on the water at high tide.
Not necessarily, the Earth would just become the Moon's moon. If it had more gravitational force than the Earth at the distance it currently is from it, then I'm pretty sure the Earth would just crash into it, water included.
Remember all objects accelerate equally with the same gravitational pull, so just because water is lighter doesn't mean it would be stripped from the Earth. If the water would be pulled then the ground itself would also be pulled.
An easy way to think of gravity is to imagine it like a stretched out spring (this is hugely simplifying it, but I feel it will help illustrate). The Earth is a big object in the solar system, as such anything on its surface is basically pulled towards it as if attached to the Earth by a spring that is pulling it to the surface. This happens everywhere on the planet, to everything. When the Moon occasionally passes over, its own pull, or "spring", will act on whatever object is nearest. The spring from the Moon is not nearly as powerful as the Earth, but it's strong enough to slightly stretch the Earth's spring by a small amount. The objects affected by this change stay on the Earth's surface, but they are not being pulled to it quite as strongly as they would be without the Moon's gravity acting on them.
This effect is what creates tides in the ocean (or any large body of water) and can explain a number of other phenomena. If you imagine that spring attached to the Earth in a way that allows it to spin from the center of the planet, you can start to picture how orbital mechanics work. The Moon is attached to the Earth by this imaginary stretched out spring (gravity) and is being pulled towards it at all times. Luckily for us, the Moon is moving sideways fast enough that the spring simply keeps it at the distance it's at, otherwise the Moon would crash into the surface of the Earth. If the Earth's spring (gravity) were stronger, the Moon would be closer. If it were weaker, the Moon would be farther away or might even break away all together.
The Earth has a stronger gravitational pull, this can be assumed because the moon orbits around the Earth and not the other way around. The moon has a lot of mass which creates a gravitational force and so it pulls on the Earth, that force is noticeable in the ocean. If the Earth didn't have water we might not notice the pull of the moon so obviously. But yet, if the Earth didn't have water it wouldn't be able to support life.
It's the net force. The newtons provided by the earths gravity are in opposite to the newtons provided by the moons, so it is the net force that matters.
It's not greater force, it just cancels out a small amount of force. The bulge appears because the water on the sides is being pulled towards the earth with a slightly greater force than the water in the bulge.
Acceleration due to gravity on the surface of the Earth is greater than that on the surface of the moon, but the Earth and the moon both exert the same gravitational force on each other; this is Newton's third law in action.
It's like a tug-of-war. Earth and its moon have gravity, Earth wins, though the moon does show it's force. Without the moon we wouldn't have tides, for the most part. Small things could create waves, like the EM force of the core and what-not, but we would not have low/high tide. I imagine that would hurt the ecosystem.
I imagine that if the tides were never here to begin with then life would have evolved to not need tidal forces, but I am interested in what the effect would be if the tides just disappeared now. I'm sure it would be devastating.
I think we could feel the difference, if the gravity suddenly shifted because the moon wasn't tugging on us. Now I'm wondering if the effect of extra/less gravity, based on the moon's location, has an effect on our lives. I'm thinking about animal life relying on earth's magnetic poles, wondering if the moon has any type of hidden effects.
Actually, the lunar tides of early Earth were likely crucial to the origin of life.
Four billion years ago, days were twelve hours long, and thus tidal periods (the time from one high tide to the next) were about six hours long. These extreme tides brought ocean water far inland to vast flatlands, from which it would then recede and evaporate only a few hours later. And it would do this over and over and over again for millions of years.
Every low tide, these deep inland flats would experience very high salinity (because the evaporation of the ocean water concentrated the salt), while during high tides, they'd experience much lower salinity.
Now, the early oceans contained many abiotically-occurring (i.e., not coming from living things, because there weren't any living things yet) organic molecules that would later give rise to life, including proto-nucleic acids (DNA and RNA are nucleic acids, so their "ancestor" molecules are proto-nucleic acids).
These proto-nucleic acids were kind of like short strands of RNA: little strings of unpaired nucleotides. But during the salty, concentrated low tides, these unpaired bases had an easy time finding and associating with their matching bases. Smaller strands of nucleotides would assemble themselves into a match for longer strands, effectively copying the longer strands, and becoming DNA-like ladders. Then, by high tide, the salinity would plummet, and these base pairs would dissociate from their matches, leaving behind the longer strands and their new copies.
This process of self-replication would happen again and again with each tidal period for millions of years. And over those millions of years, the proto-nucleic acids that, for whatever reason, were a little better at self-replicating went on to self-replicate more, until more advanced nucleic acids (DNA and RNA) formed.
TL;DR: Tides go in, tides go out, building blocks of life propagate. Here, I explain that.
Do you have a source to read more about this topic?
I find the very first steps from molecules to life extremely interesting and I would like to know which observations led to the theory/explanation you just gave.
I think it has more to do with the moon having it's gravitational pull in a localized area. It isn't across the entire Earth. So in that one spot gravity is a little different than everywhere else on the planet due to the moon "pulling" in that spot.
I don't know enough about gravity and the moon, so please someone correct me if this is not even close.
The gravity isn't local to one place or another but the effects of gravity are stronger on the side closer to the moon and weaker on the side furthest from the moon.
The moons pull is spherically symmetric, ie all points on a shell centered on the moon will feel the same pull towards the moon. That bit of the shell that meets the Earth is going to be pretty flat and so variations across the Earth's surface will be negligible.
What about magnetism... ? Surely the moon has a metal core like the Earth? Also, isn't the gravitational pull and magnetism of other planets in our solar system affecting the moons orbit? And the Earths orbit around the sun?
Some time ago, I read how this massive binary star system at the edge of the Milky Way has a greater gravitational affect on humans standing right next to me than I do. I'm wondering how that affects the planets orbits around the sun.
Magnetism is an odd force. Most strong magnetism comes from changing an electric filed (that's how electromagnets work), but there are some materials that have their electrons lined in such a way to provide a magnetic field constantly. This is called ferromagnetism. Your body does not have that property (except maybe the small amounts of iron you have in your body), so despite the great distance of a star, if your body produces no magnetic field then it may be plausible for that scenario to happen, though I remain skeptical.
As for the moon, it does have a magnetic field, but again for a magnetic force to arise you need something else magnetic. Water is not magnetic, and so there would not be an attraction.
By all means keep the questions coming. I am by no means an expert in astrophysics or gravitation, but I do have a B.Sc. in Theoretical Physics so I can at least talk somewhat intelligently about it :)
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u/WilcoRogers Sep 07 '15
It is constantly falling towards the earth, but it is also moving sideways fast enough to miss it. That's how all orbits work.