# Questions tagged [tidal-effect]

The force on parts of an extended body in a non-uniform gravitational field, due to residual gravitational attraction between the overall effect on the body and the expected effect on the point in question. Tidal forces are most notably in large moons orbiting near their primaries.

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### Does Earth really have two high-tide bulges on opposite sides?

The bit that makes sense – tidal forces My physics teacher explained that most tidal effect is caused by the Moon rotating around the Earth, and some also by the Sun. They said that in the Earth and ...
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### Moon's pull causes tides on far side of Earth: why?

I have always wondered and once I even got it, but then completely forgot. I understand that gravity causes high and low tides in oceans, but why does it occur on the other side of Earth?
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### Why is the Moon considered the major cause of tides, even though it is weaker than the Sun?

You have likely read in books that tides are mainly caused by the Moon. When the Moon is high in the sky, it pulls the water on the Earth upward and a high-tide happens. There is some similar effect ...
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### Are we slightly lighter during the day and slightly heavier at night, owing to the force of the Sun's gravity?

Using $g = \frac{Gm}{r^2}$, the force on a point mass located at 1 AU from the Sun ($m = 2 \cdot 10^{30} \text{ kg}$) is about ~0.006 N/kg. Does that mean that, e.g., a 70 kg person is ~42g lighter ...
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### Short of collision, can gravity itself kill you?

Imagine that you are falling into object with huge gravity (i.e. black hole) that does not have any atmosphere. The question is - before you hit the ground, can the gravity itself (which would be ...
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### Are there tides in the atmosphere?

Analogous to the tides of Earths oceans, do the Moon and Sun cause our atmosphere to bulge in what could be described as a low and high tide?
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### Why do some location on Earth have only one tidal maximum per day instead of two?

Most places in the ocean have two high tides and two low tides per "day" (~25 hours). But I remember reading that some locations only have one of each per day. This answer has some great explanations ...
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### Why aren't satellites disintegrated even though they orbit earth within earth's Roche Limits?

I was wondering about the Roche limit and its effects on satellites. Why aren't artificial satellites ripped apart by gravitational tidal forces of the earth? I think it's due to the satellites being ...
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### Why do tidal waves appear so suddenly in some rivers?

As tide approaches in lower part of some rivers (e.g. Ganges), a several feet high tidal wave enters from the sea against the flow of the river (making a great noise), and the water level suddenly ...
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### Can we run out of gravitational (tidal) energy?

I read an article on energy forms and sources that made me think. Energy comes from somewhere and is limited in various senses. It's most obvious for fuels: we burn coal and oil and at some point we'...
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### Why does the Moon face Earth with the same side?

I know that the rotation period of the moon equals its revolution period. It's just so astonishing that these 2 values have such a small difference. I mean, what is the probability of these 2 values ...
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### Does bottle water rise a little bit on full moon days?

High tides and low tides are caused by the Moon. The Moon's gravitational pull generates something called the tidal force. The tidal force causes Earth—and its water—to bulge out on the side closest ...
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### When a planet is heated through gravitational pull, where is the energy taken from?

Jupiters moon Io is heated through the gravitational pull of Jupiter, but when Io is heated because of this, where does that energy come from? How does conservation of energy work for this effect, ...
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### How can the Moon have such a strong effect on the ocean?

The gravitational acceleration on Earth is approximately $10 \mathrm{m}/\mathrm{s}^2$. Compared to this, the tidal effect of the Moon's gravity gives a local variation in the acceleration of ...
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### Are tidal power plants slowing down Earth's rotation?

Are tidal power plants slowing down Earth's rotation to the speed of the orbiting moon? (1 rotation per 28 cca days) Are they vice versa increasing the speed of moon orbiting by generating some ...
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### How come the Sun's gravity can hold distant planets in orbit, but cannot rip humans off Earth?

The sun is strong enough to keep gas giants close, but why not people?
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### How quickly was the Earth rotating 250 million years ago?

The Earth is slowing at a rate of $4.7\times10^{-4}$ miles per second every 100 years due to tidal forces of the moon. See: http://en.wikipedia.org/wiki/Earth%27s_rotation http://imagine.gsfc.nasa....
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### Why Aren't Saturn's Rings Clumping into Moons?

While reading with my son about how a Mars-like planet collided with the early Earth that resulted in our current moon, it said the initial debris also formed a ring, but that ring ended up getting ...
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### Why would black hole rip me apart?

According to my understanding of General Relativity, gravity is not a force and an observer which is falling freely under the influence of gravity should be considered inertial. Now, I have come ...
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### I was told that if the Moon had a retrograde orbit, tides would have a faster rhythm. Why is that?

Would this be because tidal deceleration causing the Earth to spin faster or are there other actions in play that I haven't considered? Would the Earth even spin faster because of the tidal ...
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### Why don't lakes have tides?

There's a tidal effect that we can clearly observe in oceans, which is the effect of gravity from the Sun and the Moon. If gravity affects everything equally, why don't lakes have tides?
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### Why does the moon drift away from earth?

I once saw on TV that the moon is slowly drifting away from the earth, something like an inch a year. In relation to that the day on earth what also increase in time. I wonder why is that?
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### Is the distance between the Sun and the Earth increasing?

$M$ = mass of the Sun $m$ = mass of the Earth $r$ = distance between the Earth and the Sun The sun is converting mass into energy by nuclear fusion. F = \frac{GMm}{r^2} = \frac{mv^2}{r} \...
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### Thought Experiment - Poking a stick across a Black Hole's Event Horizon

The classical explanation of a black hole says that if you get to close, you reach a point - the event horizon radius - from which you cannot escape even travelling at the speed of light. Then they ...
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### Is the length of the day increasing?

In Frontiers of Astronomy, Fred Hoyle advanced an idea from E.E.R.Holmberg that although the Earth's day was originally much shorter than it is now, and has lengthened owing to tidal friction, that ...
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### Tidal Lock Radius in Habitable Zones

Much is made of finding exoplanets in habitable zones, locations with orbital semi-major axes permitting water in the liquid state. Habitability may be compromised if such bodies become tidally locked,...
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### Does the moon affect the Earth's climate?

So, this morning I was talking to a friend about astronomical observations, and he told me that lately there has only been good weather when there was a full moon in the sky, which was a shame. I ...
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### Why is the orbital resonance of the Galilean moons stable?

It is well known that the orbits of Ganymede, Europa and Io are in a 4:2:1 resonance. Most online sources (including but not limited to Wikipedia) say that such an orbital resonance, along with the 3:...
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### Why can't one see tidal effects in a glass of water?

Why can't one see the tidal effect in a glass of water like in an ocean?
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### If water is essentially incompressible, why are there tides?

So recently we were taught in school that tides are formed because the moon 'cancels out' some of the earth's gravity, and so the water rises because of the weaker force. But if water is not ...
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### Why do we always see the same side of the Moon? [duplicate]

I am puzzled why we always see the same side of the Moon even though it is rotating around its own axis apart from revolving around the earth. Shouldn't this only be possible if the Moon is not ...
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### Is the lay explanation of the equivalence principle wrong?

The common explanation/trope for the equivalence principle always has something to do with you being inside an elevator or spaceship, and your supposed inability to differentiate, say, gravity from a ...
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### Where does tidal energy come from?

Kind of an odd, random question that popped into my head. Tidal energy - earth's ocean movement, volcanism on some of Jupiter's moons, etc. - obviously comes from the gravitational interaction between ...
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### What is the most efficient way to travel between tidally locked binary planets?

Suppose that there are two planets of roughly the same volume and mass are orbiting each other. What would be the most efficient way to travel from one to the other? In other words, what kind of ...
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### How large can planets or moons appear?

In many artistic impressions or movies there are pictures or scenes where the sky is filled with an enormous moon (as seen from a planet) or vice versa. I wonder if there is an upper limit to the ...
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### What would happen if the Earth was tidally locked with the Sun? [closed]

I'm thinking of writing a short story set on a version of Earth that is tidally locked to the Sun. I'm not exactly sure how to research the topic. Here's a number of questions about what would happen: ...
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### Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?

If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect ...
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### Will Neil Armstrong's moon boot marks really last for thousands of years?

This question concerns the residual heat (if any) contained within the Earth's moon. At the time of the Apollo moon landings, it was widely reported that the boot marks left by the astronauts would ...
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### If the moon was twice as big but twice as far away, would there be any difference?

I'm just going to go ahead and steal this question question directly of Reddit since I have more trust in the answers I get on this site. So, if the moon was twice as big but also twice as far way, ...
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### Will the increasing distance between Moon and Earth result in speeding up or slowing down of Earth's rotation period?

Problem The Moon tidally brakes Earth's rotation, and as a result distances itself away from Earth as a result of conservation of total angular momentum*. Certainly, tidal braking slows the rotation ...
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### Is there any dynamical reason for the winter solstice to happen close to the perihelion?

When the winter solstice arrives, the angular momentum of the Earth, its orbital angular momentum and its radius vector with the orbital focus in the Sun are in the same plane. This happens quite ...
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### Can you tell just from its gravity whether the Moon is above or below you?

If you are on a place of Earth where the Moon is currently directly above or directly below you, you experience a slightly reduced gravitational acceleration because of Moon's gravity. This is what ...
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### Measuring tides in a swimming pool

The tidal range of a perfectly fluid inertialess ocean on the Earth (taking into account lunar tides only) is approximately half a metre: this is the range between "high" and "low" points of an ...
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### Event Horizon of Supermassive Black Holes

I'm going to ask/explain this as best I can; I'm sure I have some fundamentals wrong here. Spaghettification is a phenomenon which occurs only in stellar-mass black holes owing to the immense gravity ...
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### Tidal force in equivalence principle

The inertial frame of reference in a gravitational field is defined locally, but couldn't a sufficiently sensitive instrument detect tidal forces in the gravitational field and thus make the frame in ...
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### How can the tidal force due to a black hole tear apart the observer inside?

I have heard that the tidal force of a black hole can tear apart an observer. But if the spacetime fabric is really stretched out near a black hole, isn't the observer also a part of it? Surely, he is ...
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### How long was a day at the creation of Earth?

Since the earth is slowing its rotation, and as far as I know, each day is 1 second longer every about 1.5 years, how long was an earth day near the formation of earth (4.5 billion years ago)? I ...
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### How many hours will there be in a day 5,000,000,000 years from now?

It is known that the moon is moving away from Earth 2cm a year, and in doing so makes the days longer. I want to know how many hours will have one day, when our planet is near its end.
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### Does the Earth's core have tides?

Does the moon produce a measurable tidal-effect on the Earth's (liquid) core? If so, how strong is it? Would it play a factor in other geological effects like earthquakes, volcanoes, etc?
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