What is Tides: Definition and 74 Discussions

Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.
Tide tables can be used for any given locale to find the predicted times and amplitude (or "tidal range"). The predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry (see Timing). They are however only predictions, the actual time and height of the tide is affected by wind and atmospheric pressure. Many shorelines experience semi-diurnal tides—two nearly equal high and low tides each day. Other locations have a diurnal tide—one high and low tide each day. A "mixed tide"—two uneven magnitude tides a day—is a third regular category.Tides vary on timescales ranging from hours to years due to a number of factors, which determine the lunitidal interval. To make accurate records, tide gauges at fixed stations measure water level over time. Gauges ignore variations caused by waves with periods shorter than minutes. These data are compared to the reference (or datum) level usually called mean sea level.While tides are usually the largest source of short-term sea-level fluctuations, sea levels are also subject to forces such as wind and barometric pressure changes, resulting in storm surges, especially in shallow seas and near coasts.
Tidal phenomena are not limited to the oceans, but can occur in other systems whenever a gravitational field that varies in time and space is present. For example, the shape of the solid part of the Earth is affected slightly by Earth tide, though this is not as easily seen as the water tidal movements.

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  1. P

    Calculating Tidal Range (Gravitation)

    Consider only the Earth-Moon system, where both the Earth and Moon are spheres. A horizontal line joins the centres of the Earth and Moon. Consider a point P that lies on the surface of the Earth. The line joining P and the centre of the Earth meets the horizontal line joining the centres of the...
  2. PeterDonis

    A Tidal effect of Sun on Earth

    It's well known that the tidal effect of the Moon on the Earth causes the Earth's rotation to slow down and the radius of the Moon's orbit to increase over time. However, the Sun also exerts a tidal effect on the Earth, which should also contribute to slowing down the Earth's spin. This raises...
  3. K

    I Sublunar and antipodal tides

    Please explain high tide at antipodal side as described in Wikipedia https://en.wikipedia.org/wiki/Tide diagram. At the sublunar side of the earth, sea water is attracted by the moon causing a high tide. On the antipodal side of the Earth sea water is also attracted, somewhat less since the...
  4. J

    B Tides and Local G: Investigating the Relationship Through Long-Term Observations

    It occurs to me that it might be possible to determine a local value of G by observing the tides over a long-ish period. Tide height might be distributed as a normal curve, but it might have a measurable deviance. I wouldn't expect a left/right offset of the X coordinate based on G(local) , but...
  5. Buzz Bloom

    I Do Solar Tides affect Earth's Orbit?

    Solar tides on the Earth are currently approximately 1/2 as strong as lunar tides. The lunar tides affect the Earths rotation as well as the moon's orbit. Therefore it seems plausible that the solar tides would affect the sun's rotation and the Earth's orbit. Can someone confirm for me that...
  6. HenryM

    Deriving the formula for tidal generating force TGF

    i have been asked to show that the TGF acting on a 1kg mass, on the surface of the Moon is equal to: TGF = 2g.e^2.(a/r^3) Where; g = 9.81 e = radius of the Earth a = radius of the Moon r = distance between the centres of the Earth and Moon.
  7. A

    I Tides on a nearly tidally locked planet

    Non-Scientist here. Assume that you had a two body system (planet-moon, double-planet) where one of the bodies was very close to tidally locked. Say they are closely co-orbiting at 6 to ten diameters in a relatively quick 20 to 50 hour orbit. One of the planets is close to being tidally...
  8. Vitani11

    Does the sun or the moon have a greater affect on the tides?

    Homework Statement I know the moon does. I know it is because tidal forces fall off as 1/r3. But why? Mathematically, I mean. Homework Equations F = GMm/r2 The Attempt at a Solution None
  9. Evangeline101

    Astrolabe Roadstead tides - Sinusoidal Functions

    Homework Statement Homework Equations 3. The Attempt at a Solution a) The height of the high tide is 4.5 m b) The height of the low tide is 0.25 m c) Period = 12.5 hours k= 360/12.5 = 28.8 amplitude = 2.125 m vertical shift = 2.375 m phase shift = it doesn't look like there is any...
  10. T

    Book on waves and tides (oceanic)

    I needed some books for preparing for IESO selection camp and i searched net and found this link: https://www.sites.google.com/site/ineso555/reading-materials The last books on the list titled as wavesandtides is the one i am looking for. Sadly, they have only given two sample pages of the...
  11. Kid Ljungblom

    How would Earth be affected by an additional smaller moon?

    I have been looking for an answer for so long. Everywhere I look I find answers to the question how two lunar sized moons would affect the Earth's tides and so on. But I want to know, if we had our own moon, with its normal orbit, and an additional smaller moon, (or just further away from...
  12. Adrian B

    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...
  13. A

    Tidal Acceleration: What & Why + Formula

    What is TIDAL ACCELERATION or TIDAL DECELERAION? Also, could some one please explain me it's forumlae?
  14. newjerseyrunner

    Does light bend due to gravitational tides?

    I was wondering if the way that light vibrates causes it to bend slightly while moving around an object with extreme mass (on top of the bend caused by relativity.) I was drawing what I thought the path of a photon should be around a massive object, but the uncertainty principal bugged me. Am...
  15. T

    Two moons in tidal lock orbit: phases, tides, axial tilt?

    Consider the following; We have Earth with two moons in orbit (discounting the existence of our own moon for the sake of this hypothetical scenario). One moon is the size and mass of Pluto, orbiting around 70,000km from Earth. The other is the size and mass of Pluto's moon, Charon, orbiting...
  16. 2

    Differential gravitational force causing tides model?

    Homework Statement Homework EquationsThe Attempt at a Solution For a), I initially tried to consider the component of the gravitational force of the moon acting normally to the Earth's surface. This would be F=F_0 cos(theta) where theta is the angle between a horizontal line going through A...
  17. nicolauslamsiu

    Tides: Does Moon's Rotation Affect Earth?

    Apart from the the gravitational pull of the Moon and the Sun on the Earth, does the rotation of moon contribute to the tides?
  18. anorlunda

    Tidal Analysis in Florida Keys: Investigating 9 Year Periods & Anomalous Data

    I've been looking at historical tide data for the Florida Keys at http://tidesandcurrents.noaa.gov/waterlevels.html I understand harmonic constituents. In fact, I found the following data for this location. Amplitude in Feet, Period in Days, Description 0.2 1 Principal lunar...
  19. G

    Tides and Moon Gravitational Force

    We know Moon creates tides on seas.Then why doesn't Moon pull loose stones or other objects lying loose on earth?
  20. iVenky

    Why do we have two tides due to moon?

    We have two tides because of the moon's attraction on the front and back side of the earth. I can understand the reason for the attraction of the moon on the front side which causes the water to move towards the moon but I can't understand the reason that the thing happens in the backside. I...
  21. D

    Theory of tides information

    Where can I get more information on the theory of tides? http://en.wikipedia.org/wiki/Theory_of_tides I would like to see more of the derivation and explanation of the tidal forcing section in the link above. I have read the section Taylor's Classical Mechanics on Tidal Force as well...
  22. H

    Does centrifugal force caused the tides?

    First time poster, thanks for help I wonder if low tide is caused by centrifugal force at noon time and high tide at midnight? The centrifugal force pushes sea water toward the center of the Earth at day time, away from it at night time. So, a man weights more at day time than night time. Am...
  23. C

    No moon=no tides no tides=no life Is that entirely correct?

    no moon=no tides...no tides=no life... Is that entirely correct?? I was recently discussing origins of early life on our planet, the other person stated that he had read (from Prof Brian Cox I think) that: no moon=no tides...no tides=no life. Although our moon is the main influence on our...
  24. S

    Reason for two tides on Earth

    There was a thing that kept me wondering for several years, which no science teacher managed to explain. Why does gravitational pull of the Moon causes two tides on Earth at the same time? Would'nt it be more logical for the tide to only occur directly under the moon, nowhere else, because...
  25. A

    Q about moon and sun tides, energy related to comet strikes and the mass water?

    Please see attatchment for qs. I really need help with number two mostly.
  26. S

    High Tide & Moon: How & Why?

    I was just wondering how high tides occur and happen to read the wiki article at http://en.wikipedia.org/wiki/Tide but I am bit confused like if the moon caused the tide then why there should be a high tide on the opposite side of the Earth also. The figure in the article is just confusing and I...
  27. A

    Effect of gravitational tides on the moon

    Ocean tides are considered to be mostly caused by the force of gravity from the Moon. Tides are presumably caused by the difference of the force applied on the "front" and on the "back"of the Earth. Meaning, gravity from the Moon cause Earth's shape to become elliptical in the plane of the moon...
  28. C

    Ocean tides and earths surface.

    I am reading George Gamow's book on gravity and in his book he says: The American physicists AA Michelson found from his experiments that every 12 hours the the surface of the Earth is deformed by one foot, as compared with a 4-5 foot deformation of the ocean's surface. This seems...
  29. J

    Cosine functions and tides

    Homework Statement High tide at 4am with a depth of 6 meters. Low tide at 10 am with a depth of 2 meters. Model the problem using the equation to show the depth of the water t hours after midnight. Homework Equations y= A cos(Bx+C) +D The Attempt at a Solution: I am not getting...
  30. T

    Solar vs Lunar Tides: Explaining the Difference

    I have a question about the effects of solar and lunar tides. I know that the effect of lunar tides is twice that of solar. However when I calculated the force of gravity of the Sun on the EArth vs the Moon on Earth using F=GmM/r^2 the force due to the Sun was much greater. Can anyone help me...
  31. khurram usman

    What is the affect of moon on tides?

    i mean when the moon is full like during 10-20 of lunar month the tides are higher but y?even when the moon isn't full its still there whole in sky? what is the reason?
  32. H

    Sun vs Moon Tides: Understanding the Forces Behind Sea Tides

    Tides in sea are caused not by moon but by sun. Though the force of attraction caused by sun is much more than that by moon.
  33. T

    Correct exaggerated drawing of tides

    Hi. Some books explain tides as a result of the gravitational pull of the moon with an exaggerated drawing like A below. It seems to me that A is not correct, but B and C are more like it. Because the moon pulls all water towards it, not just one side. Which is correct and WHY?
  34. M

    Why are there two tides a day when there is only one moon?

    Something that has bothered me for a long time, if tides are due to the gravitational force of attraction of the moon, and clearly the moon transverses the sky once a day then there should only be one high tide a day not two. If the second high tide is due to the attraction of the sun then I...
  35. D

    General relativity and tides

    Hello, general relativity describes gravity not as a force (as opposed to the classical view), but as the effect of bodies following an inertial path on a distorted spacetime. How does that explain the sea tides on Earth? The moon pulls the water without pulling the surrounding land by the...
  36. T

    Tides & Gravity: Would Earth Still Have Tides Without Moon?

    If the moon didn't exist, would the Earth still have tides? Well, yes of course. Due to the sun. But what stumps me is how often would those be... I thought every 6hrs...because that's the time the sun's max gravity effect is in the other quarter of the earth...
  37. I

    How is it that the sun affects our tides?

    I've read that along with the moon, the sun also has an effect on our tides. I understand how the moon would have an effect on tides, but I don't quite get why the sun would. According to my physics book, when something is in orbit, it's really just in free fall around the thing it's...
  38. O

    Tides, rotations and spins

    I want to ask here if tidal forces can in a sense be considered as the opposite of the centripetal forces that drive rotations or spins. I'd appreciate any web-accessible references about this. First consider a uniform spherical cloud of non-interacting test masses falling radially toward a...
  39. F

    Gravitational Model of Tides: Earth and Sun Potential Addition

    I have a question about the gravitational model used to describe tides: Is it correct to simply add the tide potentials respectively due to Earth and sun as most people do? (see for instance a good example of this approach in Eq 9 of: http://arxiv.org/PS_cache/physics/pdf/0701/0701301v1.pdf)...
  40. L

    Tides homework problem

    Homework Statement Hello, I am a French teacher who teaches physics in English. I've proposed to my pupils this work about the tides.http://vfsilesieux.free.fr/2deeuro/Thetides.html" [Broken] I would very much enjoy any kind of correction (vocabulary, grammar, ideas) to improve the quality...
  41. S

    Fe+ Brine Solution forcing by Earth Tides

    Here is a esoteric problem that is totally unique in nature: Taylor Glacier, in the Dry Valleys of Antarctica, hosts site of a Fe2+ brine solution, expressed as a rusty discharge at the terminus. There is strong diurnal signals in seismic data gathered from an array co-located there, not...
  42. B

    Does the moon cause the flux and reflux of the tides?

    I assume wind is also a factor but would the gravitational pull of the moon be the main force behind the oceans tides? To be honest I have no idea what even causes the wind so go easy on me if that was a dumb question.
  43. J

    Where does the energy to create tides come from?

    Hi, I wonder if any of you can help, probably a very simple answer, but here goes... The gravitational pull of the sun and the moon cause the tides, correct? I also understand that energy cannot be created or destroyed, also correct? Since the orbit of both the sun and the moon are constant...
  44. K

    Why the Tides Increase Earth-Moon Distance

    why tide force makes distance between Earth and moon longer?
  45. S

    Why are tides stronger at

    Why are tides stronger at the new moon for a few months and then it changes back to having tides stronger at the full moon?
  46. R

    Tidal Float Generates Electricity: Is it Practical?

    could this float generate enough electricity to be practical
  47. Philosophaie

    Measuring Sea Level: Tides, Elevation & Distance from Earth's Center

    Is there a median sea level that the logs of sea level data is based? I know the moon causes the tides which upsets the equilibrium on a constant basis. I need this sea level to be based upon the distance from the center of the Earth so with the elevation of a particular city on the Planet...
  48. M

    Sun vs. moon - affects on tides.

    In class today, we calculated that the amount of gravity between the sun and the Earth is 180. This is far greater than the amount of gravity beteen the Earth and the moon. So why does the moon affect the tides rather than the sun. My take: the sun is much farther and has a broader pull...
  49. A

    Amplitude of two components for tides.

    The tidal range of spring tides is about 3.2 m and tidal range of neap tides is about 1.8m, Assume the only tidal components are m2 and s2 tides. i.e 2 tides per day due to the sun and moon. Find the amplitude of these components and also find the maximum phase angle between the m2 tides and...
  50. C

    Understanding the Moon's Role in Tides

    Hi all! I was just wondering if anyone can explain me why the tides (created by moon effect) are created on opposite sides. (image is on attachment) Thank you.
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