Why are there TWO high tides per day?
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- Äas pĆidĂĄn 15. 06. 2024
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We all learn that the tides are caused by the Moon pulling on the Earth's oceans. So how come there's two high tides per day but we only have one Moon?
00:00 - Introduction
00:35 - One Moon, Two High Tides?
00:54 - Is it the Sun?
01:07 - Spring Tides
01:16 - Neap Tides
01:42 - The Earth-Moon Barycentre (centre of mass)
02:45 - Planetary wobbles
03:09 - Detecting exoplanets with star wobbles
03:20 - Wobbles create centrifugal force
04:29 - A lunar day of 24h50m
04:56 - Brilliant
06:06 - Bloopers
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đ©đœâđ» I'm Dr. Becky Smethurst, an astrophysicist at the University of Oxford (Christ Church). I love making videos about science with an unnatural level of enthusiasm. I like to focus on how we know things, not just what we know. And especially, the things we still don't know. If you've ever wondered about something in space and couldn't find an answer online - you can ask me! My day job is to do research into how supermassive black holes can affect the galaxies that they live in. In particular, I look at whether the energy output from the disk of material orbiting around a growing supermassive black hole can stop a galaxy from forming stars.
drbecky.uk.com
rebeccasmethurst.co.uk - VÄda a technologie
Whoa!!!! đČ The beloved BARYCENTRE!! â€ïžđ Thank you Dr Becky!!!
Spaghettification in âlinearâ free-fall motion or Spaghettification in âorbitalâ free-fall motion? hmm⊠(get you with the long words and caps-locks!) I donât know what the Earth is thinking!! but, I think Iâll stick with Dr Beckyâs explanation - thank you very much - As I have a liking to staying alive! Itâs called the tidal force, why is this so difficult for you to understand?
Thank you Dr. Becky - I could not get my head around this for years and this is the 1st time someone actually explained it so clearly! I love your videos.
And she got it WRONG!
This video (by PBS Space-time) is better and more accurate.
czcams.com/video/pwChk4S99i4/video.html
Same here
@@sureshbesra466 same here I have been trying to understand for years and it never really added up
@@strong507 Well Stephen, Iâm exceedingly happy for you and Tomas and Iâm glad it finally added up for you, because when we âaddâ the acceleration vectors at the centre of the Earth they equal zero! Thanks to the beloved Barycentre, where would we be without eh! Take care.
same here. Nobody could tell me. So thanks a lot
Interestingly, the solid ground beneath our feet also rises and falls in tides, though this is much harder to see. One way scientists have observed it is through pressure variations in oil bodies deep beneath the surface, directly attributable to the Moon. And in many high-energy accelerators in which sub-atomic particles travel at near-light speeds in tunnels beneath the ground, we need to apply corrections to the magnetic fields that guide them to compensate for the physical distortion of the ground as the Moon passes overhead. In all of these systems, we see tides
Woah! Cool! I guess I always assumed that was true but never gave it thought. Damn nature!
Yes, the Earth squishes together as the poles are compressed from tidal (directional) forces, so bulges at the middle a bit. But this confuses many people who believe the Moon is pulling. The Moon can't pull or lift water, it's smaller than Earth, and the gravity is far too weak for that. Lateral hydrostatic flow along Earth surface towards the equator is the cause of the ocean "tides". No tides in lakes or coffee cups.
It's amazing what happens when all the stuff agrees on a single direction to move in.
@@onebylandtwoifbysearunifby5475
But he clearly says that it puls
czcams.com/video/KlWpFLfLFBI/video.html
@@onebylandtwoifbysearunifby5475 the great lakes have tides.
@@glennbabic5954 I have also heard that explanation before, but the sources were less qualified than Becky. There may be some combination of the two effects at play.
This makes total sense.
Itâs extremely difficult to visualise the effects of gravity in a four-dimensional manifold, using a two-dimensional rubber sheet, in a three-dimensional time space. All you achieve is a demonstration of gravity, using gravity! Which, rather defeats the objective.
The gravitational and centrifugal effects of motion around a barycentre, both alleviate the gravimetric tensor of the earthâs own gravitational attraction, and allows water to flow in sideways from the adjoining areas to equalise the systemâŠand, we call this movement of vast quantities of waterâŠtides. All perfectly sensible. Thank you, Dr Becky.
tides explained by space time...go
@@davidmudry5622 Hello David, howâs it going? I think we first have to firmly establish exactly what âtimeâ and âspaceâ actually are? Although, we both achieved that sometime ago in our pleasant conversation. So, you already know the answerâŠbut, itâs nice to hear from you again. Take care my friend and keep critically thinkingâŠgo
@@wavydaveyparker No, I understand gravity doesn't pull only because light can't be pulled, yet light bends near a massive body. I understand when things are weightless is because no force is accelerating them, and anytime a body has weight is because a force is accelerating them. But when it comes to a high tide on opposite sides of the earth at the same time I need some help as to how space-time can explain it.
@@davidmudry5622 Oh right! I see, but you shouldnât be so down on yourself, because I donât think you realise how agonisingly close you are to solving this problem. What you just said there was exceptional, and clearly shows a structured way of thinking, very reminiscent of a certain Mr Einstein. Iâll tell you whatâŠdrop that exact comment on my video and Iâll give you a link to someone, who asked the same questions and we can discuss it there. I think the two of you have a lot in common. Take care.
@@wavydaveyparker Tidal Forces czcams.com/video/GuLL_upE4zk/video.html
Grew up in a small village on the coast. Tides can be massive. On the fridge was a tide table so we didn't get caught out by the the tide when going to Mersea Island. The Strood can really catch you.
It's not that big here where I live, but I also have it on an app. It's useful to know when to go fishing or not. đŹ
Same where I live.7 metre king tides. You really have to think about where you anchor your boat.
Dear Dr Becky, this video is exceptional and I sincerely apologise for not arriving earlier - _sorry!_ - seeing as Iâm having trouble making a video myself, to correctly explain tides to a younger audience and have only produced something to dispel the totally incorrect assumption that the Earth moves directly towards the Moon in a straight line filling up bulges. This seems like the perfect place to post my boring lengthy comment on the matterâŠso here goes! Enjoy:
When Isaac Newton first proposed the theory of Gravitation in his _âPrincipiaâ,_ around 300 years ago! He unfortunately, neglected to give us the mechanism by which _âgravityâ_ worked! However, he did provide us with some very beautiful and simple equations, to correctly calculate the movement of Planets. His problem started with his acceptance of _âabsolute timeâ_ and distinguishing the difference between _âgravitationalâ_ and _âinertialâ_ mass, which he considered to be equivalent, but being the genius he undoubtedly was, he agonised over that conclusion and knew it might not be completely accurate.
It wasnât until Albert Einstein around 200 years later, that we were finally given the more complete answer to gravity, when he told us that the natural state of things is _âfree fallâ_ ... and the _âmassâ_ of an object had the potential to curve the space around itself, within the confines of his proposed idea of _âspacetimeâ,_ which he presented in his brilliant theory of General Relativity.... _I hope that helped?_ đ
As for the tides... Well, theyâre not that difficult to understand really? Think of it like this... At the very centre of the Earth, there is a centripetal âforceâ of gravity pulling it towards the Moon... And there is also a centrifugal âforceâ _(I use the term loosely, because itâs a âapparentâ force in an inertial frame, but the Earth-Moon system is definitely a rotating, non-inertial frame and it exists)_ due to the inertia of the moving objects wanting to continue in straight lines!
These two effects âbalanceâ according to Newtonâs Third Law and the orbits continue, because the ânetâ forces at there centres are zero. The centres of the Earth and Moon are indeed moving on spacetime paths, and donât experience a ânetâ acceleration, because they are in free-fall around each other, but still under the influence of a non-uniform gravitational field.
When we work out the tides, we use the âtidal forceâ equations, which effect an object from the centre outwards.
Therefore, âNo!â pulling, or tugging away from oceans or moving towards the moon filling up bulges is necessary. Just the knowledge to realise that the Earth-Moon system operates like any two-body problem.
Of course, we then have to correctly apply the method of resolving these associated acceleration vectors into there respective components and recognise the buildup of sideways pressure in the underlying water column, which is what actually drives the tidal systems, but thatâs not my particular area of expertise?
Take care and thank you so much for making this video.
Kind regards, Wavy đ.
WRONG WRONG WRONG!
Just so completely WRONG!
Yes, Iâm afraid what you say is a bit of a misunderstanding. Look up Laplaceâs Tidal Equations, which are differential equations that are still used today to accurately predict the tides. There is no involvement of any vertical or axial components, or centripetal forces. The tides are raised by the horizontal tractive forces in the plane of the oceans. Earthâs gravity swamps any vertical components by a factor of about ten million, but the horizontal components of the Moonâs gravity are at right angles to the Earthâs field and arenât swamped. They are tiny, but crucially they are cumulative over thousands of square miles of ocean, and above all are convergent and are acting on an incompressible fluid. These factors combine to raise tides of a few metres in magnitude and also account for the second or antipodal tidal bulge due to the symmetry of the off-axis forces. The second tide is smaller due to the greater distance from the Moon. The Euler-Laplace model explains why tides donât arise in small bodies of water and correctly models the domed shape of the tidal bulges. Itâs a closed book. Thereâs an awful lot of rubbish on the web purporting to explain the tides, hardly any of it is correct, yet this was all solved by Euler and Laplace over 200 years ago.
@@oneeleven7897 Oh really!! So, youâre saying that Newton and Einstein are wrong are you! Well I happily pitch either of them against your Euler and Laplace equations any day. You obviously didnât read the whole commentâŠat no point did I say that the water is pulled upwards. I even said at the end we have to resolve these acceleration vectors into the horizontal and vertical components and neglect the vertical component, because it is overwhelmed by the earthâs own gravitational attraction. The barycentre is a fundamental, undeniable fact of nature, the earth and moon are both in a freefall motion around their common centre of mass, which Einstein spent ten years contemplating about before publishing his general theory. Are you really going to try and go up against that? Under General Relativity! Gravity isnât considered as a real force either! Gravity and Centrifugal forces only appear in an accelerated frame of reference, one that is non-inertialâŠwhere the apparent force becomes valid. Maybe you should look up the Jean Le Rond dâAlembert principal - it states, that at the centre of an object in rotational motion we can consider the centre of the object as having zero net acceleration. Please read the entire comment again and reflect on what you said? What I said here, did not go against the Euler-Laplace equations in the slightest, as they were both great mathematicians which I still admire greatly.
@@oneeleven7897 And Iâll continueâŠI also said that to work out the tides we use the âtidal forceâ equations, which actually donât involve centrifugal forces only the gravitational differential. Please try and keep up! Orbital motion is a whole different ball game and does involve dâAlembert forces. And Iâll also add that Dr Beckyâs video here is a perfectly valid explanation for the *equilibrium* of tides. If youâve got a problem with that, then I suggest you take it up with her or make a video yourself, which illustrates these wonderful and totally correct Euler-Laplace equations you keep telling everyone about. Take care.
@@wavydaveyparker Dr. Becky clearly claims in the first few minutes of this video that the sub-lunar tide is caused by the Moonâs upward gravitational pull and that the antipodal tide is caused by a centrifugal force. This is completely wrong. The tides arise from the horizontal tractive forces that I have already mentioned. The effect is subtle and could be said to be counterintuitive because the Moon is from our point of view âupâ in the sky so might be assumed to pull things up towards it. The real mechanism is like squeezing a soft ball around a circumference; it will distort on both sides of that circumference into an approximate ellipsoid. Newton was the first person to assign the tides to the Moonâs gravity but was unable to produce a mathematical model for them, as he too missed the subtlety of the effect. It was Euler who first worked out he truth, and later Laplace who derived the partial differential equations that accurately account for and predict the tides. So Newton was half right, and there is no need at all to invoke Einstein as it all works perfectly well in the low field classical limit. If you choose to picture the tides under General Relativity thatâs fine but it makes no practical difference. The Euler-Laplace model of the tides remains the definitive explanation, and this is not subjective but is the history of science.
A brilliant question Stephen. Yep! The earth and moon are both moving further apart, by approximately 4cms every yearâŠso, the tides will gradually decrease over time! And the length of a day on earth will increase by approximately 1.8 milliseconds every century. This will continue until the earth and moon are no longer in orbit around the barycentreâŠbut, that wonât happen for a few billion years yet, and the Sun would have extinguished itself by then, so donât worry about it! Ok! đ
Actually, while it's true that the Earth had been slowing down century by century, that was only true until recently when it began speeding up again and days began to get shorter once again culminating in the shortest and second shortest days on record on june 29th and 30th, 2022, respectively , since the start of the use of the atomic clock.
most scientists believe that this increased rate of rotation is probably explained somewhere between the Chandler Wobble and Glacial isostatic lateralization (the melting of polar glacial masses due to Climate change reducing mass pressure on the Earth's crust on the poles exerted by Glacial masses.
It may not be long-lived and we may go back to steadily and slowly increasing day lengths/slower rate of Earth's rotation, but for the time being days are getting shorter and the Earth is spinning faster despite the Moon's enlarging orbit.
It may surprise a lot of people that the centrifugal âeffectâ has something to do with tides, but itâs really just âInertiaâ in action, and all the matter in the Universe is accelerating away from each other, at an ever increasing rate (?) because, the gravity is unable to negate the expansion.
I prefer to describe things strictly in terms of inertia rather than using the term centrifugal force.
@@JarredDavidson And I totally agree, although I prefer to describe gravity strictly in terms of inertial mass curving spacetime, and as inertia herself once told me, _"the doors a jar, but it doesn't matter, because we're only travelling at 4mph."_ Those people who think inertia hasn't done anything good for us, should just go home, and take all those great tapes and albums...and burn them! What do you think about that then?
The universe isn't accelerating away from us. All matter is accelerating away from each other; where gravity isn't so strong that it negates the effect.
ââ@@bluegold21 Brilliant! I stand corrected, and will make the appropriate correction in due course. You're absolutely right. In my defence however, I would like say that I only wrote this comment in response to the one below mine, which said there was no acceleration (?). Would you mind if I use your informative reply on my cartoon about the misperception of tides? Thanks
@@wavydaveyparker No biggy. Pleasure is all mine. Only in the science community can one discover the magnanimity that you exhibit.
âCentrifugal forceâ? I can still hear my physic professor shouting âDonât call inertia a force!âđ
(I get itâs a question of referenceâŠ.).
Many thanks for the best tide explanation I have seen so far đ
Aye, there was also a voice in my head shouting "centrifugal force does not exist!!" too.
It's a lack of centripetal force! Our physics teacher chastised anyone who dared utter the word centrifugal.
Sorry for spamming this link, but Dr. Becky's explanation is actually not complete and actually a bit misleading in my opinion. Space Time a couple of years ago presented a much better picture of what is actually happening. czcams.com/video/pwChk4S99i4/video.html
And may not be correct! (See a Neil Degrasse Tyson 'Star-talk' video on it)
@@Chris-hx3om link?
In the CZcams video, *âWhy are there two high tides per day?â* the speaker _(Dr Becky)_ says⊠the earth is not static during all of this, and is in an orbital motion around a common centre of mass, called the barycentre. So, if we look at the gravitational and centrifugal effects closer to the poles, which are nearly tangential to the earthâs surface. Then, they are both right to claim, that these forces CAN accumulate to produce the observed tides.
I love the way you explain concepts. The questions you ask and the way you link all the components to clarify the explanation. This video is awesome but uses Southern Hemisphere orbits(clockwise). Could you also make one for Northern Hemisphere with counterclockwise graphics? The students of Georgia, USA would be very grateful!
That is a really brilliant comment, but must admit that I'm now completely confused. I might leave this to Dr Becky's expertise, seeing as she is in the northern hemisphere, and I'll just go and fly my battle kite instead. I thought the graphics were going counterclockwise, I must have been watching this, while standing on my head. Thanks for the heads-up! I wondered why I was beginning to feel dizzy.
You are seriously a world treasure. Thank you for giving us these amazing concepts in ways that we can understand!
The two tides are of approximately equal height on both sides of the globe shaped planet, because in the *equilibrium* of tides theory, the centrifugal effect is the same across the whole earth, whilst the moonâs gravity diminishes with distance by the inverse square. đ Thank you.
That doesnât seem to make sense.. I remember that the centrifugal force would be F=m \omega^2 r, where the angular velocity \omega is the same across the whole earth (1 rotation per month), but the distance to rotation center r is different, since (as Dr Becky pointed out) the barycenter of the earth-moon system is not at the center of the earth, but about 2/3 of the earth radius to the moonâs side. This would mean that the centrifugal force at the far side would be 5 times as high as the close side of the earth to the moon.. right?
@@CM-cr8wq Hello CM, thank you for the reply, you do realise that I have made a short video, which attempted to dispel the ridiculous claim and fraudulent myth, that centrifugal force was incapable of having any *real* effect in a dynamic Earth-Moon system, and instead they performed some crazy start-stop motion towards each other? And, that I'm more than willing to continue any discussion with you there...if you can find it? đ
Anyhow, I will provide you with an answer to your interesting question, seeing as no one is that interested in critical thinking anymore, and it only seems polite of me to do so...
You're equation for the centrifugal force is entirely correct, and it's just your definition of the Inertial motion that needs to be re-evaluated. The Earth's motion around the CM (đ Common Centre of Mass) or the Barycentre, is *not* a rotational motion. It is a translating motion, or as Dr Becky described, an Orbital Motion, which implies one complete revolution per monthly cycle.
Whereas, with the Earth's axial rotation, the value of (r) would increase towards the equator, increasing the centrifugal effect, as you correctly suggested, and reducing the effective *'weight'* of an object at that point.
With orbital motion around a barycentre, however, every point of mass on or within the Earth, will map out a circle of equal radius (r=4671km) as it completes one revolution around the CM.
Therefore, the centrifugal force will remain constant across the Earth, during this monthly cycle, assuming that the orbital path is perfectly circular?
I hope that was helpful, and apologise for the lengthy use of numerous words, but it does become increasingly boring having to repeat myself over and over, without any reward for my efforts. Best wishes and kind regards.
â@wavydaveyparker in other words.
The earth spinning on its axis while it orbits the sun is what creates the tides. There is no gravitational attraction between the earth and the moon. This was disproven by multiple experiments on earth and the moon.
The earth is orbiting the sun in a counterclockwise direction. The entire mass of the earth is being accelerated in a counterclockwise direction with the sun as the center of the frame. As the earth rotates on its axis, the ocean is accelerated first in a clockwise direction in respect to the Earth's orbit and then a counterclockwise direction. This creates the daily high tides.
The annual high tide occurs the first of the year as the planets elliptical path brings it the closest to the sun. As shown by Kepler's Laws of Motion, the Earth's ocean experiences the greatest rate of acceleration on the side opposite of the sun causing the water to be lifted into a higher radius/orbit.
The surface of the earth does not experience the same amount of acceleration from pole to pole. This is why the tides are more pronounced at the equator.
To reiterate. The moon has no influence on the Earth's ocean's other than the reflected light.
â@@wavydaveyparker Thanks for the reply!
I am not sure I quite understand you when you say "With orbital motion around a barycentre, however, every point of mass on or within the Earth, will map out a circle of equal radius (r=4671km) as it completes one revolution around the CM."
How can that be? If we imagining at any snapshot of time, the distance between the barycenter (which is at a given point location within earth) and any given point on or within earth is clearly NOT the same, since the far-side of the earth is 5 times as far away to the barycenter as the close side. If the distance is different at a given time, how can they map out a circle of the same radius at a period of time?
... Unless when you say "the centrifugal effect is the same across the whole earth" and all of the above, you mean that it is the same across time instead of across space? i.e. it is the same for a fixed location (with respect to the earth-moon system, not a fixed a location on earth, since earth is rotating one revolution every day) at any time, but it can still be different for different location? The circle they map out would still be circles, but of different radius for different places? That would makes sense!
I tried to do a simple calculation to verify this:
1) The force per unit mass of water (aka acceleration) from moon's gravity would be a_g2 = G m_2 / (R_2 - r)^2,
where moon mass m_2 = 7.342e22 kg;
distance from the moon center of mass to the barycenter R_2 = D - R_1 = 3.797e5 km;
the distance from the earth's surface to the barycenter is r=1709km and r=-11046km for the closest point and the furtherest point from earth to moon respectively.
This gives us a_g2 = 3.4e-5 m/s^2 and 3.2e-5 m/s^2 in the two scenarios;
2) The centrifugal force per unit mass is a_c = \omega^2 * r, where angular velocity \omega = sqrt(G * m_2 / D^2 / R_1) = 2.665e-6 s^(-1) (i.e. 2 pi per 27.28 days), so a_c = 1.215e-5 m/s^2 and -7.847e-5 m/s^2 for the closest point and the furtherest point respectively;
3) combining the two effects, total force from centrifugal effect and luna gravity effect is a = a_g2 + a_c, which gives
4.644e-05 m/s^2 (pulling towards moon) for the cloest point
-4.638e-05 m/s^2 (pulling away from moon) for the furtherst point
on earth from earth to moon.
(Edit: Made a mistake about the plus/minus sign! I have fixed it in the above. Now the numbers agree!)
These two numbers agrees with each other nicely. So nice that I am starting to wonder if there is a mathematical reason behind this.. If it would be true as well, in an alien planet?
Thanks for listening. All the best!
âIt's obvious from your reply that these calculations of tidal accelerations means a great deal to you, and I'm thoroughly honoured that you would consider my appraisal worthy enough for you to share your workings.
Please just do me a favour and drop a comment on my cartoon, because I've worked through these calculations on many occasions, and might be able to point you in the direction of some useful resource material. Thanks again.
Addition: In the meantime, try calculating the gravitational force of the moon on the centre of the earth, and equate that against the centrifugal force of the earth's motion around the barycentre. You should find that the *net* result is a *zero* acceleration. Good luck.
Dr Becky , just started watching your shows and I am enjoying them so much. I was just talking to my brother about how tides work now I can explain it to him thanks to your wonderful clip. Looking forward to next weeks.
Probably the best and clearest explanation I have seen so far. Thx!
thanks a lot for this wonderful and simple explanation
lots of videos have uselessly complicated things
Dr. Becky ⊠fifty years in boating, including three decades in the USN, and you explained the system of tides better than anyone Iâve known.
Well done!
And may not have got it right! (See a Neil Degrasse Tyson 'Star-talk' video on it)
@@Chris-hx3om No! I think youâll find that the NdT video and this are both in direct accordance. NdT calls on the mechanism of tidal âYogaâ - whatever that is? - And Dr Becky calls on âCentrifugeâ - I know what that is? - And they both yield the same results for tides.
Yes well, both Dr Becky and Dr Tyson got it not exactly right....
Here a link to a video of PBS Space Time about this topic:
czcams.com/video/pwChk4S99i4/video.html
Itâs not flat-earthier BS, I promise!
@@Chris-hx3om no
@@jorgmintel3060 Just watched it... Excellent video, and pretty much exactly what NDT said. (And not a single mention of any barycentre)...
Thank you. Not only does this answer my question, it also does so in a way that I can understand well enough to explain it to my children.
Thank you for the wonderful comment, and I sincerely hope Dr Becky gets as much pleasure out of reading it, as I just did. Although, I would dearly like to know what the question was you had answered, and would also really enjoy hearing your children's reaction, when you attempt to explain the barycentric motion of the Earth, and the associated Centrifugal Force that appears alongside its motion through space.
As that's the point where most people get confused, but I may be able to help in that regard if you're interested? Let me know. You're welcome.
When I tell you I was wondering about this yesterday! Perfectly timed, Dr!
This explanation is much better than others, because itâs simplified to a point that is correct and easy to understand. The tides are essentially caused by the inertial motion of planets and oceans around a common centre of gravity, in a non-uniform gravitational field. I see no reason to mention the SpaceTime extravaganza here, as it only deals with a misleading static scenario of tidal forces and makes no mention of the tidal effects produced by orbital motion around the sun.
Thank you Dr. Becky, this was a great explanation! I've read about "wobble" before, mostly pertaining to the detection of exoplanets (as you mentioned), but I could never really get my mind around the idea. Seeing that time-lapse of Pluto and Charon blew my mind. It was a "light-bulb" moment for me, and finally I understand wobble. â€
I've been wondering about this for a while. Thank you!
The Bloopers are adorable.
May the force be with you!!
I'm sure many have said this already. I've tried wrapping my head around this reading, watching videos, discussing with others, thought experiments...a phenom woman in STEM explains it in 3 minutes.
Now to have her explain literally everything else.
Thank you. This was driving me bonkers.
And she got it WRONG!
This video (by PBS Space-time) is better and more accurate.
czcams.com/video/pwChk4S99i4/video.html
I'm nktnsur this is accurate thoigh..think about if nothing is pulling the water away from the earth on the other side..there has to be a force there to pull the water.
@@leif1075 You're right, nothing is pulling the water on the far side. But something is pulling the earth more than the water, hence the water is 'left behind' slightly.If you use the earth as your inertial frame of reference, then it looks 'weird', but use the universe as your frame, then it looks 'normal'.
@@Chris-hx3om the way she says it in the video makes it seem like that..but what is that something..why do you just say something..don't youbjustmeam gravity of the moon? And earth's rotational momentum maybe squeezing the land spmehwat?
@@leif1075 Would you like me to attempt to answer some of your âapparentâ confusion? Unfortunately, it appears Chris is providing you with some mixed metaphors and personally I donât think itâs helping you to understand tides correctly?
I always thought it was because of Newton's Third law. Learn something new every day.
Yes, youâre absolutely right, itâs all to do with Newtonâs Laws of Motion, as easy as one, two, three. Nothing is static in the universe, itâs all relative. The action is centrifugal, and the reaction is gravity. For every push, there is a pull, or as Einstein might say, the Earth is balancing on a free-falling bicycle, whilst itâs cycling around the barycentre, itâs just that the oceans have trouble remaining balanced occasionally. Thanks
I've always wondered this. Thanks for posting.
Best explanation I've ever heard on the two-tides question! (...and the best bloopers on CZcams)
I knew it, it wasn't because of the beers it was the centrifugal force that made me wobble at the fare!! đ€
Precisely, but it was the beers that forced you put that traffic cone on your head and buy that huge kebab on the way home!! đ
@@cybermonkeys đ»
? Fair ?
â@@johnstarkie9948 Fair's fair, you're right! But, let's be fair here, we had been drinking and the ? centrifugal ? fairground ride had a fare to pay.
An important note is that the Moon doesn't actually "lift" water. Its gravity is far less than Earth's. Water flows from the poles towards the equator, causing a hydrostatic bulging. The Moon's gravity is enough to cause water flow to change direction, but not to lift it.
This is why there are no tides in lakes or bathtubs or coffee cups.
Water is not lifted by the Moon. Rather, the tidal forces are lines converging on the Moon. The Earth is larger diameter, so those lines converge rather than being parallel. Water flow follows those lines, converging and so bulging at the equator.
Another way to consider this is as a balloon being squeezed between your hands: it bulges in the center as it is compressed.The geology below water level also feels this compression, and bulges in the perpendicular slightly. Even if the Moon was 1 meter away from Earth, it still would not lift water away from the Earth, as the Earth gravity is stronger. Hence why water reservoirs do not lift even a millimeter during High Tide.
(Maybe too technical for the video, but i meet a lot of people who were told in school the Moon actually "lifts" the water on Earth. But those teachers didn't calculate the gravity first, (obviously). They probably assumed somebody else did the calculation, because their teachers told them the same thing. It happens.)
This is also why the few lakes that do have tides, tend to be the ones with their long direction oriented north-south, and located close to the 45 degree latitude line. Lake Michigan has a very subtle tide. It can be hard to notice that it is a tide, but you can conclude that there is a cycle to Lake Michigan's level that is consistent with tidal cycles.
Eben if it could "lift" it ina sense that you describe, it would look like bubles of water floating up, not sea level rise.
(and the whole earth would shatter as well, so thats not very useful)
@@carultch "True tides-changes in water level caused by the gravitational forces of the sun and moon-do occur in a semi-diurnal (twice daily) pattern on the Great Lakes. *Studies indicate that the Great Lakes spring tide, the largest tides caused by the combined forces of the sun and moon, is less than five centimeters in height.* These minor variations are masked by the greater fluctuations in lake levels produced by wind and barometric pressure changes."
-- NOAA
Yes, it would indeed by difficult to measure 5 cm level change. Especially when temperature, air pressure, and wind dwarf that variance. Longitudinal lakes on a calm, steady day. And only then from the height of Spring Tide to the absolute antithesis... 5 cm.
Tides in the oceans however: 40 FEET in Bay of Fundy, Nova Scotia.
To quote by paraphrase Crocodile Dundee:
"That's not a tide. THIS is a tide".
@@Quickcat21MK lol, I knew a guy who went by the name "cryptman" and he was as incapable of rational thought as you are.
That is actually the effect of the Moon lifting the water. It just happens that the lift is less on the poles that on the equator (because is further away). The difference is very small, but enough to cause a current flowing to the equator.
Lakes and the mall seas, don't have this effect, because they are not big enough i the north-south direction to sense the difference , and in the Mediterranean case in addition to being "flat" north-south wise, is connected to the rest of the oceans by a very small channel, not big enough to allow enough water to bulge.
thank YOU Dr. Becky for your research. it is very helpful and healthy đ AND alertness of weather expectations
excellent editing and thorough explanation, thank you
Thank you Dr Becky,
I was only wondering about this yesterday as I walked the Fleet on the Jurassic coast of Dorset.
great description!
Yeah, this is completely right though, the far side tide is more of a centrifugal effect. The graphics are wonderful and the explanation correct. Science does not rely on opinion, itâs all about examining the evidence and looking at the facts, which are acquired through experimentation. The centrifugal effect is responsible for tides on the opposite side, and the centripetal effect is gravity, but itâs easy to get confused if you are a *chemist,* and they havenât got a clue what theyâre talking about. It wonât be published within a week, because no one is interested. đ Take care and thanks for the comment.
Always look forward to Thursday and a new Dr. Becky video. đđȘđ
Great vid Becks, I dig what you're doing.
I love your pronouncing "Wobble" it sounded like Wooble
I grew up right beside the highest tides in the famous Bay of Fundy, and had my own fishing skiff at the age of twelve -
your explanation is much better than anything else I've heard.
And I later worked as a geologist at Bedford Institute of Oceanography in Nova Scotia
The funnel shape and the shallower (shoaling) depth towards land accentuates the tidal bulge in the Bay of Fundy
One unusual effect is that during ebb flow you can catch a temporary eddy close to shore that actually carries you in the opposite direction to the tidal currents in the main channel- handy in a row boat -very localized by the current jetties or promomtories such as reefs - fly fishermen use the same technique in rivers
I am visiting my folks who live right on the ocean in Western Canada, I was just wondering this last night! Of course I knew it was from the moon but not all the exact details, you're so helpful
Best explanation of this Iâve seen. Thank you
Excellent explanation! Something I'd briefly wondered about but never got around to learning why. Thanks!
There is a huge difference between a respected *Astrophysicists,* explaining tides correctly, without mentioning the motion of our planet around the *barycentre,* or the resulting effect from any apparent forces, which maybe present in a tractive component.
And, a chemistry teacher telling you that these forces do not exist, and that the tides are solely caused by the Earth shifting position directly towards the Moon in a straight line motion, which quite frankly is totally ridiculous, and an insult to classical physics, classical music, and the obvious intelligence of any average human being. Thanks again for this interesting and accurate video.
Do you honestly think Becky is a true astrophysicist? You really are delusional.
Galileo proved the non-existence of gravity. Of mass attraction. That the earth is a 3d sphere in orbit around a central star. He correctly theorized that the tides are the result of the Earth's motion around the sun. Rotating on its axis, the Earth's mass is being accelerated outward and forward accelerating its mass into a higher orbit/radius as evidenced by the tidal bulges. The fact that it is in orbit around the sun changes the direction of rotation twice a day. From clockwise to counterclockwise. Hence, tide comes in, tide goes out. Rivers and lakes don't have pronounced tides because the bank is pushing back and dirt has more force to resist acceleration than water.
Becky is obviously unfamiliar with Kepler's Laws of Motion or she would know that the annual high tide occurs on the side opposite of the sun when the planet makes its closest path and experiences the most acceleration.
There is no interaction between the earth and the moon because mass is not an actionable force. You would still get the same tidal effect without the moon in the sky. Any competent astrophysicist would know this and not be scamming you with gravitational attraction nonsense.
So quit encouraging her to lie. Since Google refuses to flag her videos as flat earth physics, her viewers need to do so in the comments.
If Becky has an issue with that, then she can address why Galileo is wrong. Why Newton's Law of Motion, F=ma, is wrong. Why Kepler's Laws of Motion, acceleration increases as the radius decreases in an elliptical orbit, is wrong. Three highly regarded physicist, all saying the same thing. There is no mass attraction. There isn't even an equation for mass attraction. Nor any experiment that validates mass attraction. You are being brainwashed by flat earth physics. Educate yourself because Becky is just regurgitating the nonsense she was told or read in a book.
Thanks, you really know your stuff. Here, this might help ease anyone's doubts, if they have the wherewithal to grasp the concept:
The equation for mass attraction:
*F = GMm/RÂČ* ~ Newton Universal Law of Gravitational Attraction, by Sir Isaac Newton 1687.
The experiment that validated this equation for mass attraction:
*The Henry Cavendish experiment* ~ Conducted by Henry Cavendish, funnily enough! đ In 1797, which determined the average density of the Earth, and allowed us to calculate *Newton's Gravitational Constant.*
If we take the time and do some real courses in *Physics.* Then, hopefully one day, you all might become respected *Astrophysicists.* đ
@@cybermonkeys you should go back to school and learn some real physics.
Galileo proved in the 1590s that there is no mass attraction. When two objects of disproportionate mass fall at the same rate, where is the mass in the equation?
There is only Acceleration. F=ma. Mass is not an actionable force. Newton's gravitational attraction equation. That just states that mass equals mass. Where is the action?
The laws of physics are equally applicable in all frames of reference. Turn the frame horizontally. What happens then? Acceleration differences.
Gravity is an artifact of Acceleration. Your god Einstein pointed this out himself. There is no difference in the orientation of the frame. The physics is still the same.
Mass attraction came from the fact that you kids believe in a flat earth with everything else floating around it. How else do you expect to stay rooted to the ground?
Galileo's ball drop experiment-> no mass attraction
Newton's, F=ma. Force equals Acceleration. The earth spinning on its axis is accelerating its mass outward and forward creating curved space. Your are being accelerated outward. Not pulled inward. What? Do you think the Earth's mass force is greater than its acceleration force? You are a true flat earther there Skippy.
F=ma. Mass TIMES Acceleration. Mass has no force without acceleration. Acceleration is the Acceleration force. Mass is just mass. Stored energy taking up space. E=mc. You don't even understand basic math and physics because you are stuck on stupid flat earth science.
Why don't you go look at LIGO. Are the detectors being pulled towards the source or pushed out of alignment. Sounds like tractor beam technology if you can get an electromagnetic wave emanating outward to pull matter back towards it.
You have to be really dumb to believe that mass is an actionable force. It's F=ma. Not m=a.
Take a pan of hot water. Now add some ice (mass) do you get more acceleration-> increase in temperature?
Go back to school there kid. You have a lot to learn yet.
By far the best explanation I've seen! I tried to understand this concept a few months ago. And between wiki, forums and other videos I got no where. You did it in 4 minutes. Bravo!
but unfortunately it's not really correct. Check the video by PBS spacetime to get a more accurate description.
@@marcelluswallace6240 It may not be fully correct for the front side facing the Moon, as the Moon cannot actually lift water away from Earth. ...
But It does give an explanation to the opposite side of the Earth experiencing tides due to inertia of rotation. A "Tides Part 2" may be good.
@@onebylandtwoifbysearunifby5475 No, the opposite side bulge is actually explained in the same way that the moon-side bulge is explained. Neil Degrasse Tyson did a really excellent video on it.
No! NdT spoke about âYogaâ - Pbs spoke about âPimplesâ - Dr Becky spoke about âCentrifugalâ - they are all simple and correct mechanisms, which explain the far side tides. The main message you should takeaway from this video is the factual existence of a barycentre, and the fact that at the centre of the Earth the opposing acceleration vectors cancel.
@@marcelluswallace6240 here is the link to the video you mentioned:
czcams.com/video/pwChk4S99i4/video.html
Thank you DB, itâs something that has always puzzled me.
Ahhh... It makes sense now.
Thanl you very much.
Have a great day!
One thing I think you forgot to mention is the fact that gravity is dependent on distance.
The side of earth facing the moon is slightly closer to the moon so the gravitational pull is stronger than the centrifugal force.
On the other side, the moon is slightly further away so the gravitational pull is weaker than the centrifugal force.
Same effect explained in two different but equally valid ways.
@@maximilianofonseca9013 Exactly and at the centre the centrifugal force = gravitational pull = free-fall = weightlessness. Thanks
The explanation I once saw was to imagine three balls lined up vertically to the moon. Allow the balls to fall under the moon's gravity. The ball closest to the moon gets attracted slightly more than the middle ball, which gets attracted slightly more than the outer ball. The result is that the two outer balls move away from the center ball.
@@charlesgantz5865 That is an excellent way to imagine it Charles. In Physics, itâs called the âspaghettificationâ effect. Unfortunately, in your example those balls are still free falling towards the moon in a straight line. And, thatâs where the barycentre, orbital motion and the centrifugal effect of inertia suddenly appear.
@@charlesgantz5865 this is the answer!
over simplified.
the high tide (even at spring tide) is not always "under the moon" .
more over, there are places (at least one) that are within the same time zone (in fact, under 200 miles apart) where one will be experiencing a high tide, and another will be experiencing a low tide (at the same time).
tides are not caused by the pulling on the water under the moon; but more by the "squeezing" on the water from the poles and topics, towards the earth-moon line (this pull is effect by the ocean floor and land, making "irregular", but periodic).
Right, it's more like squeezing a balloon at the poles. Ocean tides are hydrostatic pressure resulting in lateral flow to a common point. Moon is too small to lift water away from Earth's core.
An excellent explanation; thankyou
Great explainer! Always wondered how this works, thank you.
Centrifugal effects are capable of causing tidal forces, in conjunction with the inverse square law of gravity. Centrifugal and gravitational forces cause very little effect on tides, especially around the barycentre.
Thank you for teaching this, it is a very accurate depiction of our twice daily tides. Tidal forces don't have to be orbital, but in a balanced orbital Earth-Moon system, around a barycentre, they are essential.
Gravity is universal and non-uniform. All parts of the earth are accelerating towards and away, from all parts of the moon at different rates, and it is causing the Earth to squeeze and not the oceans to lift.
If you want to truly understand tidal forces, then you need to understand General Relativity, because General Relativity is built upon an accurate description of tidal forces. Thanks
So a few things... first thank you for staying away from mis-leading clickbait titles on your videos. It drives me insane when science channels do this. Second, thanks for just educating us on random things. It's really fun, and this is information I didn't know I needed but now I can't wait to blow my friends minds telling them the Earth and moon actually revolve around each other. And lastly... love the blooper reels. WOBBLE WOBBLE WOOBLE WOBBLE.
Hoobble
Wobble.
And she got it WRONG!
This video (by PBS Space-time) is better and more accurate.
czcams.com/video/pwChk4S99i4/video.html
âHoobble, Wobble toil and trouble - Fire burn and cauldron bubbleâ - _Macbeth_
What a Wonderful explanation Dr Rebecca.
Thank you đ
Thank you for the excellent explanation!
Dr. Becky , I think there is 2 forces first one the gravity of the moon pulls up the oceans from one side of the earth cause the high tide and the second force comes from the rotation of the earth around its axis pushes the water of the oceans to other side of the earth cause another high tide even though it is on the opposite direction of the moon ...
no, the effect would be there even if the earth was completely stationary without any orbit, wobling or whatever
dr blocky explains that incorrectly
The problem really is that no one actually understands everything about tides. So no one can explain exactly why they work the way they do. For us common folks all we need to know is this, gravity is alive and well and tides on Earth are influenced by both the Moon and the Sun. Why would any of us need to understand it in more detail than that?
@@asthmasayshi131 It wouldn't, no. If there wasn't an orbit, the moon would crash into the earth. If there were a magic non-orbiting levitating moon, all the water would pool on the near side.
@@txmike1945 Oh hey it's Bill O'Reilly.
Hello Elias, how are you? âFor every action there is an equal and opposite reactionâ - Elias koff - 2021
thanks for that simple and clear explanation, I'm very familiar with the tides but have always struggled to understand, let alone explain, this phenomenon, which makes it awkward when teaching tides to novices! All the models I'd seen before ignored this barycentre oscillation, so the idea of a centrifugal effect never really came up in the discussions. I'll forward this link to Physics teaching colleagues at work and may link it to a video in my own channel in due course. Many thanks and here's fingers crossed for a nice balmy, breathable atmosphere on Trappist d or whatever its proper name is!
What a wonderfully clear, interesting comment and accompanying channel. Yes, Isaac Newton firmly established that a common centre of gravity was a prerequisite for all celestial bodies in balanced motion. Otherwise the outcomes would be disastrous. This wobbly inertial movement is definitely a contributing factor behind the tides, and is often overlooked by some unscrupulous individuals, although it did later require the incredible insights of Pierre Laplace to complete the picture. Many thanks and please take care balancing on bicycles.
Thank you so much for this clear explanation.
Fascinating Becky, thank you for the explanation.
Great explanation. I understood this 40years ago from physics classes but had long since forgot the details. Nice to see it explained with no resort to the mathematics.
I recently moved to a place where the tides are very high so have taken a bit more interest in how they vary day to day. It would be good to do a follow up on how the inclination of the moons orbit results in one high tide often being a bit higher than the other each day.
Ah! I didn't know about that moon inclination bit ..... thank you! Another observation now makes sense!!
Would be interesting to see how this plays out on water planets with more than one moon. Thank you for the bloopers Dr B you always know how to make us laugh!
I would like a video on this!
not really a water planet doesn't really have tides in the sens we see them on earth. Tidal forces still apply of course, but there are no visible local effects.
sloshing. Lots of sloshing around.
@@MusikCassette So we need a bit of land mass to better measure the tides. But the whole point would be the different moons magnifying or cancelling out tidal effect.
Sort of like the sun and moon but more layered on top of each other. The moons would likely be in orbital resonances so you'd get one killer tide at some interval!
That was well explained and a well made video. Thanks!
I have watched dozens videos that try to explain this phenomenon and this is by far the easiest to understand. Your students are in great hands Dr. Becky.
and is also wrong
One other interesting thing about tides, they donât effect rivers or lakes. The actual tidal forces are minuscule, the only reason why we see tides at all is because the water allows circumnavigational flow of water. This allows basically a standing wave to rotate around the world. If the flow of water was blocked off then the tidal forces would be virtually imperceptible. As it is the current tidal bulge is just over 50cm (1â 8â). It is higher on coast lines and river outlets for the same reason tsunamis are small bumps in the deep ocean but huge waves on land. It amazes me on how weak gravity is and yet its influence goes so far.
Right, the Moon doesn't "lift" or "pull" water away from Earth. It changes the flow direction. All the water flowing towards the equator causes the bulge due to hydrostatic pressure. Water flows towards the equator because the Earth is larger than the Moon, so those force lines converge towards the center.
It's amazing what happens when a single direction is agreed on. Be it tides, or magnetism, or tornados and hurricanes. Motion is the same magnitude, momentum is conserved. But when it all agrees on a single direction: it's nothing short of amazing.
It also amazes me that tides still work even though there are multiple landmasses blocking water from flowing around the Earth near the equator - South America (plus Central and North America for a big blockage in the northern hemisphere), Africa (plus Eurasia for another northern blockage) and Indonesia. The tides require a significant current to move water to where the high tides are - mostly the high tide itself moving, but that's clearly complicated by the land masses. The only major current that circumnavigates the globe is around Antarctica. I would have thought there's some degree of tide circumnavigating the globe around the Arctic too - there's no continent, the ice is floating on the surface so water can flow underneath and the ice is presumably vertically mobile, and that ice doesn't always reach Canada, Greenland, Scandinavia and Russia anyway - but I don't see anything marked around the Arctic on maps of ocean currents. So yes, it's pretty impressive that there's enough flow to maintain this standing wave, given that the tidal forces are highest at the equator which is obstructed by land. I guess that depends on the Pacific, Indian and Atlantic oceans covering large chunks of the equator, leaving enough room for tides to occur, and creating enough pressure to maintain the needed currents around the barriers?
â@@onebylandtwoifbysearunifby5475 The whole planet deforms, as does the moon. It's just that in rotation the solid part of the Earth is attempting to pass through the much more fluid oceans.
"they donât effect rivers or lakes" - nope. Larger lakes can experience tides. See for example the North American Great Lakes. It's just that the tides on said lakes are much smaller than ocean tides.
@@stevehorne5536 There are certainly strong global oceanic currents. They are strong enough to maintain direction of flow through tides. The longitudinal directions are not to be overlooked. There isn't much obstruction between N and S hemispheres, most of the landmass is in the Northern hemisphere. So the flow in largely N-S unobstructed. Where it meets land, there are tides of course. But water pushes equally in all directions. Water pressure increases with depth, not surface area. (And even the surface area is 70% water). Pressure equalizes in all directions, pushing the water higher where there is more of it. Persistent force and small accumulations make a startling difference, yes. It's not something one would predict as obvious.
One interesting thing to think about is how pressure increases on deep sea life at high tide areas. All that water stacked on them probably is rather noticeable. Probably a lot of cycles we don't even know about in marine life.
Aren't tidal forces themselves involved as well? Water on the opposite side of the Moon would be slightly further from it than the Earth itself, and hence pull would be a little less, so water would "lag" behind, causing a tide.
Tidal forces are the correct explanation because they elongate the objects, in this case the Earth, even if they do not rotate. Gravity and the centrifugal force are conveniently influencing the right sides of the Earth relative to the Moon in Becky's explanation.
Tidal forces are the correct explanation for tides, but if they didnât revolve around the barycentre together, then they would accelerate towards each other and the tides would rapidly increase, until collision. In Dr Beckyâs video the tidal forces are taken relative to the centre of the earth outwards, because that is the zero reference point.
Thank you so much for explaining this it was terrifically eye-opening.
Thank youâŠ..Nicely explained with simple physics and good animationsđ
And Becky's explanation may not be correct! (See a Neil Degrasse Tyson 'Star-talk' video on it)
Thank you. There are so many âtides explainedâ vids that donât discuss the barycenter and the centrifugal force of the opposite tide.
And when I point to a Dr Feynman vid describing the barycenter and opposite tide I get hand waved off.
Once upon a time there was an âAtomFoolâ who said, that he respectfully disagreed with Feynman?
I always thought it had to do with the fact that the Earth is in free-fall around the Earth-Moon center of mass, which cancels out the component of the Moon's gravity pointing directly toward the Moon's center of mass, leaving only the inward-pointing component due to the fact that the lines from the Moon's center of mass to the different points on the Earth are not parallel. The Sun's tidal influence on the Earth is less because being so much farther away, those lines are closer to parallel, and the inward component, after canceling out the component that points toward the sun, is smaller.
This is correct but misses some things.
On the side of the planet facing the Moon, the gravitational acceleration caused by the Moon is stronger than that applied to the planet as a whole, so you could think of it as water falling slightly away from Earth - so you get a tidal bulge.
On the side opposite the Moon, the Moon's gravity is weaker, so the acceleration applied to the water on the far side is less than the acceleration applied to the planet as a whole. The end result is the planet itself falling slightly away from the water, so you get a tidal bulge on the far side as well.
But since the planet and the water sticks together by Earth's much stronger gravity and molecular bonds, this tidal force makes itself apparent as a "stretching" component - essentially it puts the whole planet under tension, not just the water on the surface.
Additionally the inward-pointing component applies a compressive force on the globe. As far as tides are concerned, you could also look at it as the gradient of gravity applying a tangential acceleration to water all across the globe, pushing water towards the high tide bulges and away from the neap tide recesses.
On top of that there is the centrifugal effects from the fact that Earth is rotating around the Earth-Moon barycenter, but that effect *stacks* on top of the tidal bulges caused solely by the gradient of gravity.
@@HerraTohtori Another thoughtful comment. Well done! But, can I politely suggest one slight correction? You said, _âThe end result is the planet itself falling slightly away from the waterâŠâ_ That should read, âThe end result is the water itself falling slightly away from the planetâŠâ Because at the centre the opposing accelerations cancel. The Earth is in free-fall and the whole planet receives an âoutwardâ acceleration to balance the Moonâs gravitational attraction, which is weaker on the far-side. Itâs really very simple.
@@wavydaveyparker It's all relative! The important thing to realize is that the difference in gravitational acceleration points away from the surface on both sides. I was attempting to use the linguistic inversion to highlight that, from the perspective of the water on the far side, Earth is being pulled more towards the Moon than the water itself is, leading to "planet falling away from the water" - or, in reality, leaving the tidal bulge slightly higher.
@@HerraTohtori
Thank you. That makes sense.
@@HerraTohtori Yes, it is all relative! At the centre of the Earth the acceleration vectors cancel, just like Daniel described. The tidal force acts in an outward direction from this point. There is no need to mention any other perspective. Itâs unnecessary baggage.
WONDERFUL topic, and explanation - Professor Smethurst.
Amazing explanation, thanks!
Off topic, but I wonder if the barycenter being so far from the center of the Earth helps generate the dynamo that creates our magnetic shield
I think if we didnât have a unusual big moon (compared to other planets) we might not have a liquid molten core in the earth. Those tidal forces are massaging the earth and slowing down the cooling of the earth core. And certainly without a liquid core, no magnetic field, no protection against solar eruptions, loss of atmosphere. Mars has no big moon -> no liquid core -> no magnetic field-> a very thin atmosphere. I never thought of the barycenter being far away from the center being essential for the dynamoâŠI donât know, but yes I think you might be correct in that assumption.
Hmm, I watched and read a lot of explanations about the physics of the tides. And most of them - especially on the internet - *does not match with physics textbooks.* Even some physics websites and Becky oversimplify it. Some sources are totally wrong. For those interested in the physics of tides, a good (school) physics textbook is recommended. It is much more complicated than described here or on some websites or YT videos.
*In short:* It is the resultant acceleration due to the superposition of the tidal and centripetal (or centrifugal if you will) accelerations. Combined these push the water perpendicular from the earth-moon line to the two water mountains along the earth-moon line, like squeezing a pimple . So, both tidal bulges are caused by the same accelerations, not different ones as mentioned here. Because not only tidal acceleration, but also centripetal or centrifugal acceleration acts on every point on the earth, not just on one side. Of course, this is also simplified. But so it is written in physics textbooks.
A pretty good brief visualization can be found at www .geological-digressions .com/wp-content/uploads/2018/08/tides-forces.jpg?ssl=1 (remove the blanks) If you want to stick to YT, PBS Space Time âWhat Physics Teachers Get Wrong About Tides!â (watch?v=pwChk4S99i4) is a good starting point. But even this video lets some questions unexplained. You can't avoid picking up a physics textbook.
PS: I'm not usually the type to explain their job to professionals. And I am also aware that Becky cannot reading along all comments.
Hello Schlaf, why didnât you mention my âdaftâ little video in your excellent appraisal? where did you go? I was all ready to discuss the ins and outs of tides with youâŠand then you disappearedâŠanyway, youâre right! dr becky probably isnât reading this, but I just wanted to let you know that I did, and found it all very interesting. Apart from the *fact* that the Earth and Moon are both in a *freefall* orbital motion around a *barycentre* and *not* accelerating towards each other in a straight line, as is depicted in many incorrect tidal explanations. Thank you and take care.
@@wavydaveyparker _"... why didnât you mention my âdaftâ little video ..."_
Because I did not know it before and it criticizes only one point of an explanation in another video if we mean the same one. And this is not a problem in Becky's explanation.
_"... and then you disappeared..."_
I assume you mean the video from Atomic School. It was a pretty long time ago and I don't remember getting a notification on my comment from YT.
_"... the fact that the Earth and Moon are both in a freefall ..."_
Exactly. But that wasn't explained incorrectly by Becky.
@@schlafschafweb Yep! Youâre rightâŠit was a long time ago, but Iâd remember that sheep anywhere! Youâre more than welcome to comment again, because I was attempting to address your concerns over the pbs video you, and everybody else keeps mentioning. The real key to this whole tidal thing is *Balance* - No balance! No Universe! No Universe! No us! Itâs just that the oceans are temporarily out of balance twice a day in some places? Whilst the whole Earth remains balanced in its motion around the common centre of gravity.
I agree. Her explanation was pretty incomplete... The video you linked is the most complete explanation I've seen. But in his video, he also fails to mention the wobbling of the planet in the Earth-Moon barycenter and the centrifugal force that it causes.
But still, the MAIN explanation is simply the "gravity differential (or tidal force)" between the different points on the planet, but also the fact that the water gets "squeezed" by it... So I think his video is better.
So, essentially what your saying is that youâd like to see a tidal explanation video, or read a definition in a scientific journal, that says, the tides are caused by the inertial momentum of planets and oceans, in orbital motion around a common centre of mass, in a non-uniform gravitational field. That gives rise to a tidal force from the centre outwards, and tractive acceleration vector components, that accumulate pressure across the surface of the water. Well, unfortunately that doesnât exist presently, so youâll just have to content yourself with watching both of these correct explanations in conjunction with one another. Good luck
Very informative video!! And very thorough!!! đ
Outstanding explanation of something I never really understood. Thanks!
Not quite right. It's differential pressure and hydraulic forces that cause tides. PBS Space Time covered this many years ago.
Here's a link maybe:
czcams.com/video/pwChk4S99i4/video.html
Yes, but the auestion is then: what is creating the differential pressure?
And the answer: is the gradient of gravitational forces.
No need for rotation amd centrifugal force.
@@gehngis did you watch the video? It's tiny tangential forces that squeeze the oceans, rather than huge vertical "pulling".
â@@MrGonzonator Yes, and what I said does not say otherwise.
Both the squeezing and the pushing/pulling are caused by the shape of the moon gravitational field.
My point is that there is no need to invoke rotation or centrifugal forces, unlike @DrBecky does in this video.
I live by the sea, its amazing. Tides are weird, yet no tides in the med???
Hi Dr. Becky, are you SURE that's an accurate description of the principle forces involved? Doesn't sound right to me. My understanding is more closely related to the gravitational effect of the Moon diminishing with distance, plus the fact that the earth is (comparatively speaking) a rigid body - so the whole thing moves, whereas the body of water can display its experience of those gravitational forces by distorting (a lot more than the Earth does).
Itâs not wrong what she said, but itâs not the full explanation.
I highly recommend this CZcams video of PBS Space Time:
czcams.com/video/pwChk4S99i4/video.html
@@jorgmintel3060 I mean it's not wrong, but if it isn't the main factor, then it's kind of wrong. But it's a good lesson in humility for all of us who fell into that trap :) (assuming she notices these comments and makes a corrective video)
Great explanation, and I love the bloopers bit!
Wow, great video, thanks so much
Hm, now I am confused. I learned that the Tidal Force is responsible for this effect of tides. Does this seeming "disagreement" have to do with different frame of reference being observed?
I am confused about your confusion. Why? Tidal Force is the result of Centrifugal Force + Gravitational Force. Both those forces act in nearly the opposite direction on any place of earth. So if you simply add up this both forces the result would be close to zero. You have to do it in an vector addition, so they don't cancel each other out completly. The resulting tiny vector represents the direction and strength of your tidal force. This only works because the angle between those two forces is less then 180°. This is also the reason why the tidal force of the moon is so much bigger then the tidal force of the sun. Although the gravitational force of the sun measured on earth is many times higher than that of the moon. It's ultimately all about the angle between the vectors.
Yes, good point.
"Tides" are hydrostatic forces due to cumulative directional water flow, not "lifting". The Earth gravity is stronger than the Moon, so no lifting away from Earth surface. Smaller bodies don't lift larger ones. Rather, the Earth is larger diameter than the Moon, so the tidal forces converge towards the center, causing a bulge at the equator. This bulge is largely symmetric, hence the "tides" on the opposite side. That plus the barycenter rotational forces of the Earth-Moon system mentioned in this video. It's both, but mainly hydrostatic (lateral) water flow towards the equator.
You should look up the video on tides by PBS Spacetime. It goes into much more details. Tides are mainly caused by the oceans flowing towards the equator rather than being lifted up by moon's gravity. Other phenomena like the ones mentioned in this video are minor contributors. I'm no expert but this video seems incomplete
And Becky's explanation may not be correct! (See a Neil Degrasse Tyson 'Star-talk' video on it)
Oh God are you saying centrifugal force create the opposing tide???
That's the biggest misconception about tides.
Even a stationary system with no rotation would have 2 tides. The gradient of the gravitational field is enough to explain both tide.
Just like when falling into a black hole one would get spaghettified, not just half spaghettified.
@@perseverancerover
No, it is not a perfectly valid explanation.
And no you do not need rotation or any sort of movement to have 2 tides.
Tidal forces simply arise from the fact that the gravity force changes with the square of the distance, it does not need movement to take effect.
That's basic physics. And the Wikipedia article on tidal forces is enough to understand there is absolutely no need for movement.
@@perseverancerover Just go read the formula for tidal force and tell me where you see the speed or rotation appear in this formula (spoiler alert: they do not).
And if you cannot read equations just go watch the PBS video on tides. They explain very well how the shape of the gravitational field creates a pressure gradient on the water on Earth which translates into water level difference. No need for movement.
@UCSgdjTSWiZT8MZTCmom46gw
Ok, that's my last response, because obviously you do not understand the basic of physics.
We are not having a polite discussion. I am trying to educate you while you make an effort to not understand.
The gravitational force is in 1/rÂČ, because it is in 1/rÂČ any non punctual object placed in a gravitation field "feels" a different force in its different part.
Regardless of its motion, the object will feel stretch and squeezed by the different values of the gravitational force.
This stretching and squeezing is what we call tidal force and it is what is causing tides and spaghettification.
Now this tidal force is in 1/r^3.
And when I say that you make an effort to not understand is that obviously you went to look for the equation.
Instead of seeing that speed and motion does not appear in the equation, you jumped directly to the 1/r^3. Felt clever to have something to say I am wrong.
But you failed to understand that
1. I was talking about gravitational force, not tidal force.
2. Would it be in 1/rÂČ or 1/r^3 it does not change that the speed does not appear in the equation.
Oh and free fall motion, is like no motion at all. And free fall motion is only mentioned to justify we can change referential so that we can ignore the first term in 1/rÂČ.
Brilliant explanation!
Ah never thought of that. Great video!
Sure the earth feels no force as it's travelling in a straight unaccelerated line along it's geodesic. Although, that's "net" unaccelerated. I suppose tidal bulges are parts that are being accelerated temporarily, as they are not at the centre of mass, rotating etc, but aways from it, but it all balances out.
That is actually a blindingly good comment Paul. Accurate and concise. You even managed to smuggle in the word âgeodesicâ - brilliant! Itâs just a shame some people wonât understand what you meant and just say, âCentrifugalâ doesnât exist. Thank you.
So itâs centrifugal force that causes the other bulge , Thank you Dr. Becky for this explanation. I am an engineer but never properly understood this 2nd bulge. That Rose & Jack spinning around dance scene was killer explanation đ
hi. is that a scammer?
That is also unfortunately not the main explanation for that second tide, it just coincides with it (see pbs or ndt videos about this). I've been thinking that myself with complete certainty for years and realised a month ago that I was wrong. Seeing a youtuber & scientist I respect doing the same is making me feel a bit better now though ^^
@@dkey201 I had already seen their videos, unfortunately I was not convinced by their explanation. But after seeing Dr Beckyâs I understand now that all those videos are ultimately talking about centrifugal force, they just donât know it đ.
Let me explain, using Jack and Rose analogy.
1)Jack and Rose suddenly pull each other ( not yet spinning around) , what you will see, Rose hair suddenly flying outwards, well that is centrifugal force. So, in earth-moon scenario , that is 2nd bulge.
2)Jack and Rose now start moving around each other while pulling each other . You will see again , Roseâs hair again flying outwards, thatâs centrifugal force.
So all those tidal forces which pbs video was saying are just gravitational pull and centrifugal force(virtual force) created by this gravity . And centrifugal force is imaginary, so itâs just gravity and motion of moon that cause tides
@@sureshbesra466 That was an excellent appraisal Suresh, and seeing that âdâkeyâ hasnât respondedâŠplease let me interject! What youâve described there is the perfect explanation to âInertiaâ in action. Thatâs what centrifugal force is - The tendency of a object to want to continue in a straight line, but is pulled by a force at right angles to its motion, which results in an orbit. Quite simple really!! đ
Now, if youâd like to hear what Einstein actually thought his General Theory was actually all about! ⊠đ ⊠Then youâll have to comment on my video instead. đ Take care.
Thank you so much!!!
Finally somebody explained it!!
I never seen it explained so well, nice. well see ya in a week for JWST's first photos
earth's gravity is stronger than the one on the moon BUT the moon is pulling earth ? how come ?
Hello Dominic, The acceleration due to gravity at the surface of the earth is 9.8m/s2. The acceleration due to gravity at the surface of the moon is 1.6m/s2. However, the pulling force between the two is the same, because gravity is proportional to the product of both the masses and indirectly proportional to the square of the distance they are apart. Does that help or would you like me to use actual numbers?
@@wavydaveyparker wow clear 10/10 ! i love when people knows their stuff and can easely explain it ! man science is a good thing for healt !
@@DOM_4GOOD wow, thanks very clear 10/10 ! It was nothing really đ just the simple use of F=ma, but your great question did get me thinking about some follow up questions. Maybe youâd like to drop a comment on my channel and we can work on some more simple math together. Thank you for replying. Take care.
*[Enter your asinine and vacuous remark here]* đđđ And press enter.
Thank you for your contribution! đ
Seen so many videos on the topic. This is the first time I can honestly say I get it. Thanks!
Youâre welcome :)
Dr becky has a great personality
In the CZcams video "what physics teachers get wrong about tides" (czcams.com/video/pwChk4S99i4/video.html), the speaker says... the grav and centrif forces (basically along the line joining moon and earth) are FAR too small to produce the observed tidal bulges. Instead, he looks at the forces somewhat closer to the poles (see that video at 5:20), which are nearly tangential to the earth's surface. He claims these forces ARE large enough to produce the observed tides.
Yes, yesâŠwhatâs your point? All vectors can be resolved into their vertical and horizontal components. The only thing that was demonstrated in the video you cited, was a stationary earth with extremely tiny forces at its surface, and about to start accelerating in free-fall motion directly towards the moon, because he forgot to mention inertia and the barycentre.
There's the wobble
Great word wobble wob woba
ââ@@barry8642 Great name barry, baz, bara..Your centre of mass must be the Bary-centre.
Love you Dr. Becky!
thanks Dr Becky I always wondered about this and didn't know why đđđ
Sorry, I have absolutely no idea what a "Double torus *OOrt cloud* magnetoglobe" thingy is? You're just making this stuff up, but I can assure you, that it had nothing to do with me.
And if I was God, which thankfully I'm not, then I would have left that bit out of my creation, for fear of being mocked, by my minions. Oort bless you.
Try to explain this to the infamous Fox News host, Bill O'Reilly, who in a news cast with an atheist said: "Tides go in, tides go out. You can't explain that!"
The atheist was so baffled, he didn't know what to say, in reply to such stupidity.
It would've been a more interesting exchange if Bill had actually done his research and found an example that scientists currently cannot explain.
Thank you for the video.
Great explanation.
Sorry Becky, but this explanation is simply wrong. PBS Spacetime made a video about this years ago (czcams.com/video/pwChk4S99i4/video.html). The second bulge is caused not be centrifugal force. Actually the pulling force of the moon on the water doen't act on the bulges outwards. It acts on the inward bulges. It pulls the water closer to the ground and the water displaces other water and that water gets "lifted".
We need to get these comments higher, I'd like to see a second video from becky realising about being mistaken! I really think as a scientist & influencer, this is one of the most interesting topic she can discuss (the search for the truth, research in the internet era, and the fact that even the most intelligent and qualified people can be very sure of themselves and very wrong, even close to their own field of expertise)
Nah. As the guy says in the video, tidal acceleration is not real, its just an apparent effect produced by our constantly moving frame of reference. The same is true of centrifugal force. Her explanation and his are just different ways to imagine the same thing. Also, his claim that the effect is mainly caused by the sea being pulled in the middle seems off, to me. You can clearly see from his diagram that the forces "pulling" on the sea are significantly greater than the forces "pushing" on the sea.
Earth's equatorial bulge is about 43 kilometers (27 miles). The equatorial bulge means that people standing at sea level near the poles are closer to the center of Earth than people standing at sea level near the Equator.Ocean has bulge?Earth has bulge ?Bulge within a bulge?
This vlogđ„ đtook a year to pop in to my streamđ.
Compared to your comment?đđ
You seem very obsessed with bulges. Next you'll be telling us Everest is a bulge. đ So, I'll just play along with the bulges for now. Yes, gravity causes a bulge, and Inertial motion through bulging space (also known as centrifugal bulging force) causes a bulge. So, the Sun causes two bulges and the Moon causes two bulges, and at full and new moon we get four bulges for the price of two bulges, with bulges moving within bulges. And the earth spins on its axis causing a equal bulge right around the equator.
Having said all that, we don't actually notice any of these bulges, or pass through them twice a day, because they are extremely tiny and actually only exist as bulges of tidal energy that dissipate through the oceans and around the surface of the Earth causing Tides.
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ââ@@eduardoamor1753 You're very welcome eduardo đđ but, to clarify I think I should add that all these apparent bulges, manifest from the centre of the earth, *outwards,* as it spins on its axis, whilst also revolving with the bulging moon around there barycentre, and all whilst that same barycentre, orbits around the Solar System barycentre with the bulging Sun, which probably gets 'spots' from all the bulging? đ
â@@cybermonkeyssome people just shouldn't be allowed to do physics. The moon has nothing to do with the tides. Nothing. Back in 1971, Scott dropped a hammer and feather on the moon proving that there is NO gravitational attraction between celestial objects. None whatsoever. This should have settled the gravity as a force debate waging since Galileo dropped balls from the Tower of Pisa back in the 1590s. But a bunch of flat earthers wrote Galileo's findings off as a thought experiment leading Newton to his gravitational attraction nonsense which later discombobulated Einstein into his nonsensical relativity and warped space bs.
The tides are strictly the result of the Earth's motion in space as theorized by Galileo. The equator has more acceleration causing the ocean to be accelerated to a higher orbit/radius. The Earth is also in motion around the sun causing a change in direction of acceleration of the ocean twice a day. The highest tide of the year takes place the first of the year on the OPPOSITE side of the planet facing the sun when it makes its closet pass and experiences the greatest amount of acceleration at that point according to Kepler's laws of motion.
If there was no moon, there would still be tides.
If there was no moon, there would still be *solar* tides, due to the combined effect of the Inertial motion of the Earth's orbit around the Sun, and the gravitational effect between them.
And, the tide would be highest at closest approach or perihelion, due to the increased gravity and Inertial speed of its orbit, in direct accordance with Johannes Kepler's *Second* Law of Planetary Motion.
Go back to atom-school stewie and get your teacher to take some proper Physics lessons. Good luck.
I've watched many videos about tides to find an explanation that satisfies me, and though some have good correct answers this is the first time someone mentions "centrifugal force", which is a true key word. Thank you!
Fantastic explanation!