# What is Tidal forces: Definition and 52 Discussions

The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomena, including tides, tidal locking, breaking apart of celestial bodies and formation of ring systems within the Roche limit, and in extreme cases, spaghettification of objects. It arises because the gravitational field exerted on one body by another is not constant across its parts: the nearest side is attracted more strongly than the farthest side. It is this difference that causes a body to get stretched. Thus, the tidal force is also known as the differential force, as well as a secondary effect of the gravitational field.
In celestial mechanics, the expression tidal force can refer to a situation in which a body or material (for example, tidal water) is mainly under the gravitational influence of a second body (for example, the Earth), but is also perturbed by the gravitational effects of a third body (for example, the Moon). The perturbing force is sometimes in such cases called a tidal force (for example, the perturbing force on the Moon): it is the difference between the force exerted by the third body on the second and the force exerted by the third body on the first.

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1. ### I Voids, dark energy and tidal forces...?

I would like to ask you some questions I have about some interesting work I was reading (https://arxiv.org/abs/1205.4238 & https://academic.oup.com/mnras/article/527/4/11962/7457744) where the authors analysed the effects of dark energy in the shape and evolution of voids Apparently, they...
2. ### I Why Do Stars in Binary Systems Assume a Teardrop Shape?

In binary star systems, it is said that one of the stars can assume a teardrop shape resulting from the gravitational pull of the companion star. This shape is typically portrayed as asymmetric (i.e., there is no teardrop shape on side of the star away from the companion star). Yet the...
3. ### I Are Tidal Forces Curvature of Space?

I've heard it and I've read* it before, so I just want to make sure I understand this so I never have to wonder about it again. So, are tidal forces exactly curvature of space? Here's why I think the answer to that is yes: .I've seen a spacetime interval equation which has a coefficient on...
4. ### I How Do Jacobi Fields Explain Tidal Forces in General Relativity?

Given a one parameter family of geodesics, the variation vector field is a Jacobi field. Mathematically this means that the field, ##J##, satisfies the differential equation ## ∇_{V}∇_{V}J =- R(V,J,)V## where ##V## is the tangent vector field and ##R## is the curvature tensor and ##∇## is the...
5. ### I Tidal forces acting on planet NGTS-10b

I am hoping a PF participant can help me understand why the tidal forces cause the NGTS-10b planet to fall towards it's star. I more-or-less understand why our moon's tidal forces on the Earth cause the Earth's rotation period to decrease, and the conservation of angular momentum of the...
6. ### B Tidal Forces When Falling into a Black Hole

So, if the Earth moves slowly through a large hula hoop, sensors attached on the hoop will measure some stresses, which we might call tidal forces. The faster the Earth moves relative to the hoop the larger those tidal forces are. So, if a person falls into a black hole, there are some tidal...
7. ### Calculate Tidal Force on Underwater Artwork Sculpture in Philippines

Can anyone assist. I'm workingg on a project for the installation of an underwater artwork sculpture. How do I calculate the tidal force on the structure to stop it moving on the seafloor. It's not anchored to the seafloor only sitting on it. Also what safety factor should be built into it for...
8. ### I Orbit simulations, tidal forces and planetary oblateness

How does one correct for tidal forces when (classically) simulating the orbits of solar system bodies?
9. ### I Comparison of tidal forces acting on the Moon vs Enceladus

I have heard about a moon Enceladus. Which is powered by tidal force. I suppose this force press back and forth on the moon and friction in the core causes heat. I hope I'm right :-) Now tidal force ##F_t=\frac{2GMmr}{R^3}##, where ##G## is Gravitation constant, ##M## is mass of planet causes...
10. ### I Tidal forces on a spring-mass system

Say I have two masses connected by an unstretched massless spring at some height above a planet with a strong gravitational field. Once I let go, both masses would follow geodesics in spacetime towards the center of the planet. Because the masses travel radially, the spring would compress and...
11. ### I How can the Equivalence Principle hold when we consider tidal forces?

Tidal Forces: "It arises because the gravitational force exerted by one body on another is not constant across it". which implicitly implies that the acceleration is not constant on that body. Equivalence Principle: "weightlessness sensation occurs when one free falls in gravity" - which...
12. ### A Would a larger Martian moon create a stronger magnetic field

I have read a previous forum discussing the possibility of creating a stronger magnetic field on Mars using tidal forces by putting a larger moon in orbit around Mars. My question is how large of an object would it have to be compared to Mars and how distant would its orbit need to be from the...
13. ### Exploring Feynman's Tidal Forces: A Deeper Look

I used to think I understood this - big mistake! I've just watched a great classic Feynman lecture posted by another PF user (a superb way to spend 50 mins of you can spare the time) https://www.physicsforums.com/threads/i-found-the-best-teacher-of-physics.855335/ In that lecture, Feynman...
14. ### Will this rope break due to the tidal forces or not?

While I was thinking about how tidal forces can make objects float at the surface of a planet orbiting a massive object like a black hole, the fact that any material on the Earth isn't held together by gravity only, but also by chemical bonds which give it its tensile strength came into my mind...
15. ### Time dilation magnitude in orbit around a black hole

Hello, I'm working on a hypothetical situation involving a planetary body orbiting a black hole (similar to the scenario in Interstellar, but for different reasons), trying to balance tidal forces with orbital distance and time dilation. First, I'm interested in the effect of gravitational...
16. ### Question regarding Earth, Moon and tidal forces

Homework Statement If the distance between the Earth and the Moon doubled, by what factor would the tidal forces felt on Earth decrease by? Homework Equations Not sure if there are any relevant equations F = GM1M2 / r∧2The Attempt at a Solution [/B]G = 1/d^2, if d is doubled, then G =...
17. ### How much do surfaces tilt due to tidal forces?

I've read that tides deform the Earth's crust by about 40cm. When I try to visualize the tidal bulge approaching me and then receding away from me, it seems like the local surface under my feet would tilt slightly one way as the bulge approaches, then level out, and then tilt slightly the other...
18. ### Tidal Forces in Accelerating Frames

Let's say I'm floating in space in a spaceship, and there are some stars around. Now I turn on powerful spaceship engines. This causes a huge acceleration, which causes the brightness of some stars to increase a lot. (Those stars that are up in the pseudo gravity well become bright) Does tidal...
19. ### Finite tidal forces at black hole event horizon redux

What's the best way to explain why tidal forces for an observer free-falling through an event horizon are finite? My first thought was to say that "gravity isn't a force, it's a curved space-time". On further thought, however, it seems to me that consideration of the Rindler horizon shows...
20. ### Weak Field Approximation and Tidal Forces

The weak field approximation in the Newtonian limit shows that the coordinate acceleration along a geodesic is related to the gravitational force. The geodesic deviation equation relates the coordinate acceleration between adjacent geodesics to tidal forces. If I drop 2 balls together from the...
21. ### Do tidal forces slowly make orbits more circular?

I don't understand, how can tidal forces make the orbits more circular? Perhaps it has something to do with the fact that in elliptical orbits (unlike in circular orbits) the velocity is not always perpendicular to the acceleration? Or maybe it does not have to do with the tidal forces from the...
22. ### Tidal forces and thermodynamics

If the gravitational effect of the moon influences tidal forces on earth, doesn't that violate the 2nd law of thermodynamics? If gravity is a force and not energy, and only forms of energy can convert into other forms of energy. Then how can gravity create tidal forces, which are kinetic energy...
23. ### Gravitational torque on a ring mass

What is a gravity tidal torque on a simple circular ring, inclined at some angle i? I can't find a solution for this simple problem, despite the ring's idea is frequently used in the precession problems, for example in the Earth's axis precession case. How this can be computed effectively?
24. ### How are tidal effects explained by general relativity?

I can fairly understand the concept of gravity as a curvature in space time in general relativity, but so far I could not understand completely the tidal forces explained by the curvature of spacetime. When the moon is on one side of the earth, the oceans on this side come closer to the moon...
25. ### Can black holes merge to create larger event horizons?

Hi! New here. Be gentle. Kinda an idea that popped into my head a little while ago: Are the tidal forces of some black holes powerful enough to separate quark groups? Google seems to be a bit iffy on the subject.
26. ### Dark Energy as Gravitational Tidal forces?

I’ve read a bunch of post about how the universe does not exist inside, nor is, a black-hole. Still, for my question I would like to assume the universe exists within an event horizon (actually highly curved space-time, that locally, appears flat), and has a massive singularity at the...
27. ### Moon & Tidal Forces: Earth & Titan Mysteries

Not homework here but merely curiosity. I was reading that on Titan there are rivers of methane, and that at least one is 400km long. Now I was thinking about the Earth and moon; imagine that the moon becomes a copy of Earth exactly, keeps all of it's features and becomes the diameter of the...
28. ### How do the tidal forces warming moons theories hold when []

How do the “tidal forces warming moons” theories hold when [..] How do the “tidal forces warming moons” theories hold when apart from heating from expansion, there may be also cooling from contraction? I can understand a temporary heating, from the tital forces exerted on the moon but...
29. ### Do Tidal Forces in Black Holes Affect Matter at the Quantum Level?

Theoretically; As any mass approaching the core of a black hole, then would the tidal force difference effect the quantum level and rip apart matter? Also at the very centre of a black hole would gravity cease to exert its force since in any direction the "pull" would be equal?
30. ### General relativity and tidal forces

Tides on Earth are described with Newton's theory of gravitation. Relativistic effects on tides theoretically become measurable on very strong gravitational fields, possibly becoming twice as strong as tides predicted by Newtonian gravity: http://adsabs.harvard.edu/abs/1983ApJ...264..620N...
31. ### Gravitational waves and Tidal forces

Anybody could explain me the difference between tidal forces and gravitational waves? My question emerges from the fact that gravitational waves has never been detected and also considering that tidal forces are very well understood by current physicist. Thanks AG
32. ### Relativistic effects on planetary shear [tidal forces]

before i ask my question i want to review two points: 1. place a body like a moon or a planet near a black hole, as the body approaches the extreme gravity affects the body deferentially. 2. review the tidal forces on Jupiter's moon Io leading to volcanic/tectonic consequences. now take...
33. ### Into what shape does an orbiting sphere get distorted by tidal forces?

I'm having trouble imagining how an orbiting object would get distorted by tides --- in the first instance, say, the distortion of an initial uniform dense ball of coffee grounds (of the sort John Baez likes to imagine in his web pages). I know and understand why, if it were infalling radially...
34. ### Radial tidal forces and tidal forces on moving objects redux

The following diagram and approach illustrates my recent thinking and revisiting on some of the calculations for the radial tidal forces and perhaps even the "force" during a flyby. Suppose we consider a series of geodesics , all flying by our massive object M, at points a, b, c,...z on a...
35. ### Gravitational perturbations = tidal forces?

Hey folks I'm learning about graviational perturbations on satellites due to planets and, mainly for now, the Moon. In the book I'm reading on this, they say that gravitational perturbations due to celestial bodies are not casued by the full gravitational attraction of them but only by the...
36. ### Do tidal forces mean the Equivalence Principle is BS?

From another thread this question came up: What about tidal forces? Although they could be incredibly small (and I don't think anyone denies they exist) you could conceive of a test in a closed room that detects tidal forces (if it is gravity) and when it doesn't detect them it is uniform...
37. ### Tidal forces near a black hole

Given a black hole metric g_{\mu\nu} how does one calculate the tidal forces near the black hole horizon? Is there any more quantities that may be required to answer this?
38. ### Weyl curvature and tidal forces

I'm a bit confused about this and would like for someone to help me get this straight. I read in wikipedia that a manifold with more than three dimensions, like spacetime, is conformally flat if its Weyl tensor vanishes. I think all FRW metrics are conformally flat, so I guess our universe is...
39. ### Understanding Tidal Forces & Rindler Metric

Recently while searching through some old threads in this section of the forums, I came across a few statements that do not seem to me to be entirely self-consistent. I was wondering if someone could tell me which - if any - of these declarations is not correct: -- in a uniformly...
40. ### Tidal forces inside BH in horizontal direction

Spaghettification outside of a BH rips apart objects in vertical direction, but compresses them in horizontal. Inside the BH, tidal forces rips objects apart in ALL directions - at least I was thinking so. But recently I read: http://arxiv1.library.cornell.edu/abs/0903.4717 The edge of...
41. ### Understanding Tidal Forces: An Overview

Can someone briefly describe what is meant by tidal forces?
42. ### Tidal Forces near Black Holes: Exploring Vertical and Horizontal Compression

Please confirm, I am not sure. Outside the horizon, object is torn apart in vertical direction but is squezzed in a horizontal. Inside the horizon, object is still torn apart in a 'vertical' direction, and in in the horizontal direction too
43. ### Moon's Tidal Forces puff up Earth

It is easy to show*, that the Differential (Tidal) Force, produced by the Moon, around the surface (equator) of the Earth, is: \vec{\Lambda F} \approx \frac{G \, M_{moon} \, \delta m \, R_{earth}}{D^{3}} \times \left( 2 cos(\theta) \vec{x} - sin(\theta) \vec{y} \right) The radial component of...
44. ### Tidal forces and geodesic deviation: a principle question

hi all, i kind of have a black hole regarding my understanding of the consistensy of tidal forces and geodesic deviation analysis. one can determine some coefficients of the riemman tensor from the tidal forces equations, by getting to a form that is like the form of the geodesic deviation...
45. ### Determination of Riemann curvature tensor from tidal forces

Hi, Given a large number of test particles N, it should be possible to determine the Riemann curvature tensor by tracking their motion as they undergo geodesic deviation. Is there a minimum number N that will achieve this in any situation, or does it vary from problem to problem? How...
46. ### Do Cosmological Tidal Forces Prove the Expansion of Space?

The team of Francis, Barnes, James & Lewis have published several very helpful papers in recent years about the expansion of space (with their names in various orders.) I suggested in a recent thread about their Radar Ranging article that they are trending away from explaining particle...
47. ### Exploring the Limits of Black Hole Tidal Forces: Effects on Matter and Light

If a black hole will always rip you apart through tidal effects as you approach it, what are the limits on what can be ripped apart? Will it rip apart atoms, protons, quarks? What do the tidal forces do to light? Does it "rip" light apart?
48. ### Exploring Tidal Forces - Learn about their Effects and Interactions

Hi, I'm not sure if I'm at the right place to write this message, so please excuse me if I'm not. I have read a bit about tidal forces, but I still don’t understand what they are, how they act on different body masses, etc. So, I thought I could find answers here. I would greatly appreciate it...
49. ### Curvature without tidal forces

How is spacetime curved if the present gravity field is completely uniform and there are no tidal forces. Clocks at a same height would tick the same, at different heights (to the gravity source) would tick differently. But what about space? How is space curved in the absence of tidal forces...
50. ### Tidal Forces Near a Black Hole

the questions is that: An astronaut inside a spacecraft , which protects her from harmful radiation, is orbiting a black hole at a distance of 120 km from its center. The black hole is 5 times the mass of the sun and has a Schwarzschild radius of 15 km. The astronaut is positioned inside the...