Why Do Boats Make This Shape?
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- เผยแพร่เมื่อ 21 ก.ย. 2024
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This video is about the "Kelvin wake" shape of water wakes behind boats - we talk about mach angle, dispersion, superposition of many waves, and how these all lead to the pattern of a wake. We don't get into Froude number though...
REFERENCES
Boat Wake Wikipedia Page: en.wikipedia.o...
Interactive Boat Wake Simulation: observablehq.c...
Feynman Lectures on Water Waves: www.feynmanlec...
Building up a Boat Wake from V-Shaped Wakes: editor.p5js.or...
Wave Dispersion: en.wikipedia.o...
Mach angle shock waves:
www.sciencedir...
Ship Wakes - Kelvin or Mach Angle? Rabaud and Moisy Paper: journals.aps.o...
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Minute Physics provides an energetic and entertaining view of old and new problems in physics -- all in a minute!
Created by Henry Reich
It’s amazing to see those waves come together to make the recognizable wake pattern. I didn’t know it would be that complicated but it’s really interesting to think about
Hello
Can gravitational waves make similar or really different yet beautiful patterns from which we can do some awesome science?
@@pulkitmohta8964 no dispersion for gravitational waves, I guess: they travel at a constant speed _c_ - or at least only a *very* dense matter can change that noticeably…
@@pulkitmohta8964 no because gravitational waves travel at the speed of light and u would have travel faster to create this phenomenon.
I think it is time to colloborate man
Awesome video. Way more complicated than I thought!
high there
Yes visualization makes easy to understand.
Omg
Sup Derek
Just 4 replies? last time I was this fast when I was a sperm.
Appreciating the fact that i get content like this for free.
This
not really, you are paying with your time spent on ads, still its not too much I think :)
@@ignacyn5346 be quiet
Internet bills, your PC, electricity bills, your internet router
@@creativecreepyturtle1562 the content itself is free
0:31 "In this video, we are gonna explain exactly where this shit comes from."
can't unhear it.
I don't even know what he really says. All I hear is shit
@@l.w.1014 i think it's shape
Lol, I was going to post this too but I think he said "shape".
bruh sammmeee
shift, maybe
I just noticed that for some time these videos aren't actually hand drawn like the older ones. It took me a while to notice, which means that you managed to imitate the look quite well, but I miss the drawing a bit.
Are you sure? I think they still draw some stuff like the boat, water waves and "dispersion" text.
@@2KOOLURATOOLGaming I think it’s tablet drawn with some imitation of a marker. It clearly isn’t hand drawn (if you only include paper in that) when you look at 0:40. They animated the sound waves, and there is no hand moving around like they used to have
On the other hand, this means we get more videos on a more regular basis! There's always a tradeoff.
It allows for more complex visuals.
If you look at 3:21 you can't tell that that isn't hand drown
It's a bit late at night, but they posted, so I'm now a *wake*.
Bruh over here it’s 9 A.M
@@Cumgguzzler same
Coolest dad joke I heard in a while
This isnt MinuteEarth.
Edit: All puns belong to MinuteEarth.
Mood
Years ago when I was riding a boat, I thought about a way to know the speed of the ship I was riding in. I got the idea because I knew that the angle of the shockwave of a supersonic thing relates to its speed, so I looked outside expecting a fine, singular wave. I got surprised about what I found and asked myself why. Thank you for finally answering this
Damn, I didn't even notice they all have that pattern. Thanks for making these all contents available for free.
This is so good that I though I should leave a comment to boost engagement
Yeah me too
No way, me too!
Silly TH-cam algorithm. I'll do my part for boosting engagement nonetheless.
I though so too
Hehe same😉
Lets appreciete the hours of investigating, animating, drawing... all this for free. Thank Minute of Physics
“Free” as in ads + paid promotion but yeah the gratitude is still there, it works for all.
@@yungmurakami6002 you dont pay sh*t for this quality content, that means its free.
@@kirabey8946 yes, I know I don’t pay for shit. I’m perfectly aware of that. But the channel is funded through ads and paid promotion. If that wasn’t the case, the quality and time put into the videos wouldn’t be the same, or they’d be far less frequent. You’re underestimating the fact that TH-cam is a legit money-making platform. 🤡
@@yungmurakami6002 You're focusing on the creator's perspective. From the user/viewer perspective it is without any cost, especially if you have ad blocker, which means it is free. If OP said, "let's appreciate Minute Physics releasing this for free", you'd be correct, but with their wording, you are not.
i love learning things i never knew i wanted to know
This definitely not a comment just to boost engagement because I really like this video.
+
0:39 this is a bit misleading, because light waves also disperse when not in a vacuum (which is always)
I appreciate you changing the thumbnail and title to make it more clear what you are explaining here
I had no idea he changed the title. Its only been 10 hours.
the progression in the video is just so satisfying... you get a buncha video clips, all these simple concepts, lines, wavelengths, and then BOOM you get a 3D rendering that looks EXACTLY like the clips at the start.
won't be long before we get a supercomputer to render all the particles on earth in real time.
I absolutely love fluid dynamics.
These are the questions we never ask but definitely need the answers of, and i can understand how amazingly hard it can be for someone to even think of such a question that is original and not already answered from other bigger channels , really great job mate.
Had to do a double take when he said “shit” 😂
Same here
he said shape
@@tonydai782 Source?
@@shade0636 it makes more sense considering what the captions say
@@tonydai782 Yeah good point.
Now I wanna do physically accurate wake shader !! Thx minutephysics you're always amazing and straight to the point and leaving us with just enough to dig through if we want to get deeper, but with the proper terms.
So that is how hamon works! Finally, I understood it, not even all 8 chapters of JoJo let me know the exact method, but this channel do.
Minute physics finally posts minute videos again
Finnaly one of my childhood questions are answered. Thank you physics minutes
the result was so satisfying that I started smiling at 2:55
And I started wondering, why no single videogame that includes swimming or boats got that right so far. It seems not too hard to implement. Would add a ton in terms of visual appeal.
Me too. It's so beautiful. And the way he says it, he sounds like he is happy too 😊
Excellent video and awesome graphics to illustrate a complex topic in an intuitive manner! I’m an engineer who sometimes does navigation studies (including wake generation studies), and while I’m familiar with the math, this presentation makes the concept much easier not only to understand the physics but also connect the dots between textbook drawings of waves to what you actually see in real life. Well done!
Very impressive! One little clarification for 0:43 : The speed of sound in an ideal gas varies only by temperature and not e.g. by pressure. Specifically, it is proportional to the square root of absolute temperature, which is the result of particle speeds in a Maxwell-Boltzmann distribution.[1]
It varies by altitude because temperature does, but you can't really say it's 343 m/s in dry air at sea level because sea level does not imply a specific temperature.
[1] en.wikipedia.org/wiki/Maxwell%E2%80%93Boltzmann_distribution
that is an approximation
Ayy you are uploading much more frequently now, it's great to see!
Never thought I'd be interested in the physics of boat wakes, but the way you present your content makes literally anything interesting. Great video!
WoW!!! fluid dynamics never fails to surprise me.
One of the best physics videos I've seen on TH-cam
This is a beautiful and elegant explanation of an equally beautiful and elegant phenomenon. Thanks
Doing a wave motion module at university right now and knowing a little about the actual maths behind this is lovely
This is brilliant science communicating: Very interesting topic explained in an engaging way. Thanks, as usual, Henry!
I've always wondered about this and spent any boat ride just looking at these waves trying to figure them out. Thank you for this clear and beautiful explanation.
At 0:30 it really sounds like you're saying "... exactly where this shit comes from," and I can't unhear it.
I take a boat to and from work every day. I'll never look at the wake the same way again. Thank you.
I came here to this video because of the insane Tiktok Boat Jumping challenge that cost 4 lives, after watching this, the science of wakes confirms how the body reacts to the water currents underneath that could have potentially killed them by neck breaking. We can't see much underwater, but your science explained it very well.
Great video. Never think about it in this way
Videos like this is why I love this channel.
0:33 “where this sh*t comes from”
Wasn’t expecting that one from this channel
Video was cool and all but I just wanted to appreciate the use of a very nice iv-I release in the figured bass of your background music. I'm seeing more expressive themes while still working in a universally safe sort of space, well done.
Wakes are also generated by the stern of a vessel, not just the bow. And the longest waves are generated by the ship as a whole (as if from the sides). This makes for a more complex and subtle pattern from which lots of information may be extracted. As the video illustrates, the best way to get this information is via images from above. Which especially includes satellites.
A good image will captures the wake when the contrast is highest, which means the lighting must be ideal. In this case, lighting from a 45 degree angle works best. Also, the reflected light is polarized, so even a less-than-optimal image may be improved by placing a polarizer in front of the camera that is adjusted to the angle needed to accentuate the polarization.
So, let's say we have a fairly good image from above. What can we learn from such images, even if the vessel itself isn't visible? Here's a partial list:
- Speed
- Direction
- Rate of turn (or lack of turning)
- Hull length (for larger vessels)
- Approximate draft (depth in the water)
- Approximate hull shape (particularly the presence of a bulbous nose or a flat stern)
- Approximate displacement
All the above may be determined from a single image, without having to see the ship itself! But it works best only for conventional "wet hull" ships: Hydrofoils and hovercraft have different wake signatures that are harder to interpret. Multi-hull ships (catamarans, trimarans) aren't a problem.
But what about when multiple vessels are in close proximity, such as for military exercises? Overlapping wakes are much more difficult to decode. There are many tricks that may be intentionally used to limit the value of wake imaging, particularly to make two very different vessels appear similar from above. But assuming no tricks, there are ways to determine much of the above information for every vessel in a fleet, and also do so at night. But it requires filtering out most of the wave data, and focusing only on the elements that most easily provide the information we seek. A great way to do this is by using Synthetic Aperture Radar (SAR), where a satellite sweeps an area with radio waves of specific frequencies, and which also works when clouds obscure the view.
Military folks were only the first to do this. Today, cameras and SAR on commercial satellites are used to complement the AIS (Automatic Identification Signal) sent by ships to share their location to avoid collisions. Particular attention is paid to large ships not transmitting an AIS signal, or transmitting an incorrect signal, as it can indicate problems on the ship (electrical failure, piracy, fire, etc.) and trigger a Coast Guard response to investigate. Commercial wake imaging is good enough that even military ships typically keep their AIS active at all times: It is very hard to hide a moving ship!
really really good explanation! well done
I always wondered about this ever since I was a child.. Thanks for making this.
Propulsion's toughest enemy explained to see the beauty in em.
Thanks for the content
You do a great job at explaining complicated things in a way that is understandable. Good job!
Just wow. I´m a second year physics student and I never thought about that. It´s very cool and beautiful. I think such beauty gets often lost, while leanring physics. Never the less, physics is great.
This was just... Beautiful.
I am watching this while having a online physics class with exactly this discussion going on
you have class on sundays?
Bangl;adeshi>:?
@@tommihommi1 He's probably just catching up, but I had lab work every Sunday for the duration of my engineering course.
@@_John_P my condolences. Only people putting in crunchtime for their thesis do stuff on weekends here, and the university buildings are closed on the weekend
@@tommihommi1 yeah in our country we have holidays only in Fridays
as a graphics programmer, i will definitely apply it somewhere, and this explanation gave me the exact idea how to do it.
Great way to “wake” up, a notification of a new Minute Physics video! 🙌
I see what you did there, clever.
your all videos are very helpful for all
It's so cool how the physics behind a boat wake are surprisingly complex!
Look , TH-cam notifications does work !
Noice!
Aside from the physics of boat wakes, I would like to comment my appreciation for the mathematical aspect of this phenomenon. I love this sort of example of something having a sort of geometry to it where certain aspects of its essence or function can be represented by drawing straight lines or simple angles, but overlaying a series of multiple sketches of straight lines or simple angles can yield a more complex shape that is very pretty and pleasing to look at.
There are actually some mistakes in this video:
1. Water waves do not travel as depicted and it is not the water that moves in some direction. You can best imagine water waves by imagining someone moving up and down a rope fast. (Wave length there depends on how fast the rope is being moved up and down, the faster - the more waves can be seen on the rope. That is different with water waves. I forgot how sound and light waves work exactly, but I believe light waves actually travel (duality is a word that comes to my mind, but it is too long ago that I have learned this.))
2. The waves of any water vessel can never be faster. So the person in the kayak will never see any waves moving in his forward direction. There is no bow way moving forward. Vessels always stay ahead of any of their waves (unless they slow down. You have to actually consider that, when you pass under a bridge, where there is little room at the top. You don't want your own waves to lift you against the bridge.)
3. The waves along the side of the vessel travel exactly at the speed of the vessel. It is only when they put distance between them and the ship or boat, they will start to slow down. The further away from the vessel, the slower the waves and the lower the amplitudes of them.
I am not sure, but I believe that the Kelvin wave pattern has been refuted. Don't know, if there is a newer model. Real wave systems from vessels are extremely complicated.
Monday's are quite dull in my subscriptions so a new Minutephysics video makes the whole day much, much better. 😀
Kelvin's ship wake can be computed using the Chester, Friedman & Ursell Method of asymptotic theory (and hence the wake is described in terms of the Airy function and its derivative). The semi-angle of the cone is sin^{-1}(1/3) independent of the velocity of the ship/duck (for the deep water dispersion relation omega²=g|k|).
the pattern is interesting.
now, here the hard question:
other than speed and the density and depth of the water, what causes the period of the waves? in other words, what is MOST attributed to long period, fast moving waves versus short period, slow moving waves. remove the speed of the boat, and accept that density and depth of water are moot. What actually creates the frequency of the wave?
hint: displacement
spoiler: consult a naval hydrodynamic engineer before guessing.
for another clue: examine pressure waves from submarines and inspect the differences above the hull versus the difference below the hull..
if you are thinking about "lift"...you are getting close....
if you are now thinking that the layer between water and atmosphere contains clues, you are even closer.
have fun with this one.
Wonderful! This was the most comprehensible explanation for wave dispersion I've ever seen!
might be overall one of the best short videos on physics out there.
Thanks! Over time I'd gotten lost in doing calculations and forgotten what a dispersion relation *really* is. These visual really help remind me of the physics underlying all of the math.
At first I thought this topic would be way too hard for me to understand, but this explanation made it so simple! Thanks.
So that spawns an interesting question: if dispersion of waves of different speeds exist, are all the differing speeds emitted from the motion simultaneously, or are the water particles accelerating and thus creating the wider waves longer after contact? That would explain why the wake feathers outward more further from the boat instead of closer to it
A great read to look a bit more into the topic of Waves in Water is Feynman's 51st lecture "Waves". From the Volume 1 of his collection of Lectures on Physics, which is free on the web, made available by Caltech University. Chapter 51-4 is about boat waves. I'm glad it exists. Learned amazing physics. Feynman is a great teacher!
I knew about dispersion in optics for ages and was still surprised by water wave dispersion.
Nice quick simplification of general principles Maybe on Nebula you explain why an object moving smoothly and continuously through a fluid creates waves at all. How discontinuity develops even if continuous movement. Complex fluid dynamics with Reynolds number, dual fluid interface etc.
i actually always wondered why the wake does not look like a mach cone, and i assumed that it had something to do with dispersion, but this explanation made it clear why it looks exactly the way it does.
i really enjoy the pacing in your videos. and going back to put all the components into one concept really makes for a smooth finish. love it
Another episode of things I didn't know I needed to know but know now after a well made, concise video
What a fantastic demostration of how physics is done! I mean, is incredible how a basic result like dispersion yields this apparently convoluted phenomenon. That's what a good physicist finds out!
Woah Woah Woah, I wasn't expecting 3D stuff from this channel
2:56
Just a minor note on dispersion: just as with water, there isn't really a single speed of light either. The fact that different wavelengths travel at different speeds is exactly what gets us the dispersion you might see in a prism.
Learnt about this in wave mechanics last year, but this was a very intuitive explanation. Thanks for posting!
If you really want to have your mind blown, you should search "far wake turbulence of a large ship".
Apparently really massive ships (like cruise liners) can leave behind them wakes that can reach lengths of tens of miles, and we're not really sure how it happens.
I had a professor in college that researched this exact phenomena for most of his career. He showed us so really awesome satellite images of wakes that goes for miles in the middle of the ocean.
that 3D animation was awesome!
Been wondering about this for years now. A masters degree in mathematics later and I still didn't now what's going on. And now it only took you 4 minutes to reveal this mystery. Thank you!
I miss these types of videos that explain simple yet unique phenomenon.
yeah me too.
Such a simple solution but such a complex idea i love it, great work
This is extremely wonderful! I love this video! Thank sooooooo much!
Hey V-Shape! Minutephysics here.
Fantastic visualization of a surprisingly complex topic! Thank you.
Umm...essentially, the answer is “boats make this unique pattern of wake because they make this unique pattern of wake.” This is a great explanation of what creates the Kelvin wake pattern, but it is not an explanation about why boats make waves of different wavelengths, hence speed of the waves, dispersion, that result in the Kelvin wake pattern. Apparently I need Nebula to find out, or a couple of hours studying fluid dynamics, drag, and ocean engineering.
Dispersion is something that happens when the speed of a wave depends on its wavelength. For example, when white light enters a prism, the speed of light through the material depends on its wavelength and you end up with different angles of refraction for different colors, hence the "rainbow" that forms.
IDK if you know about fourier transforms, but the point is, any function can be equivalently represented by an infinite sum of pure frequencies (cosines) with varying amplitudes and phases. There's a function called the dirac delta function. It's an impulse (think of clapping your hands and the sound it makes... it's approximate). The frequency domain representation of an impulse (unscaled) is equal to 1 at all frequencies. The takeaway here is an impulse is composed of all frequencies....
You can think of the boat as it travels through water being a train of impulse functions stimulation the water. The water will act as a filter and some wavelengths will be "accepted" by the water while others will be "rejected"/attenuated. And the boat traveling through the water isn't perfectly modeled by a train of impulses. But the overall intuition applies--the boat's motion through the water produces waves of many wavelengths, and the speed of waves in water is dependent on the wavelength=dispersion.
Not related to boats... but as far as impulse functions/frequencies/etc. something many people have heard of (musicians/producers) but don't really think about what it really is, is in guitar amp cabinet "impulse responses". Basically, an "impulse" is played through the cabinet, and the output is recorded with a microphone. The impulse contains (ideally) equal magnitude/phase of all frequencies, so the recorded output is the "impulse response", which, in frequency domain (if you fourier transform it) is equal to the frequency response of the cabinet... a function whose value at a particular frequency is how much that frequency is scaled in magnitude and phase. Once you have that impulse response on a computer, you can take a recording that's on a computer, do a convolution (math operation, same as multiplication in frequency domain) with the impulse response of the cab, and the result will sound as if it was actually played through the cab. This same theory is applied by some modern home stereo systems to "undo" the frequency response of the room the speakers are in for a specific listening location.
This is good stuff. Appreciate your efforts, Henry.
Omg, dispersion relations are so cool! In Computational Aeroacoustics, there's a whole method whose goals is to preserve a constant dispersion relation! That way, sound waves propagate correctly. (It's kinda tricky to explain in a brief YT comment, but super useful)
The single lines combining to the complete shape is magical!
that's so complicated as well as beautiful
Watching this really made my day. Absolutely wonderful!
This video reminded me of why I love Physics. Thank you so much.
Yessssssss. I've been studying this!!!! Wooooooooo. I'm stoked to see you make a video on it!
I love your concise videos, and this is no exception! I do prefer the old music better with the single bass. Having the music at a low frequency, away from your mid vocal range is less distracting.
It's wonderful how someone can explain shortly and easily something that looks obvious or complicated ❤️
That 3d animation is amazing !!!
1:27 - "Mach cone" - exactly! :o)
screw school, screw physics classes - this guy here provides all you need to know
Even if you don't understand this thing it's so satisfying to see.
Quite a tonge twister video length you put your self in Henry!
i missed watching things like this
glad im back here
Propagate might be a preferable word choice to travel. Glad to see more minute physics, the other minutes could use a break.
This was both awesome and beautiful
I dont know i needed to know this, but I guess I did, and now I do. That's some great information.