The Bizarre Behavior of Rotating Bodies
čas přidán 18. 09. 2019
Spinning objects have strange instabilities known as The Dzhanibekov Effect or Tennis Racket Theorem - this video offers an intuitive explanation.
Part of this video was sponsored by LastPass, click here to find out more: ve42.co/LP
References:
Prof. Terry Tao's Math Overflow Explanation: ve42.co/Tao
The Twisting Tennis Racket
Ashbaugh, M.S., Chicone, C.C. & Cushman, R.H. J Dyn Diff Equat (1991) 3: 67. doi.org/10.1007/BF01049489
Janibekov’s effect and the laws of mechanics
Petrov, A.G. & Volodin, S.E. Dokl. Phys. (2013) 58: 349. doi.org/10.1134/S102833581308...
Tumbling Asteroids
Prave et al. doi.org/10.1016/j.icarus.2004...
The Exact Computation of the Free Rigid Body Motion and Its Use in Splitting Methods
SIAM J. Sci. Comput., 30(4), 2084-2112
E. Celledoni, F. Fassò, N. Säfström, and A. Zanna
doi.org/10.1137/070704393
Animations by Ivy Tello and Isaac Frame
Special thanks to people who discussed this video with me:
Astronaut Don Pettit
Henry Reich of MinutePhysics
Grant Sanderson of 3blue1brown
Vert Dider (Russian CS-tv channel)
Below is a further discussion by Henry Reich that I think helps summarize why axes 1 and 3 are generally stable while axis 2 is not:
In general, you might imagine that because the object can rotate in a bunch of different directions, the components of energy and momentum could be free to change while keeping the total momentum constant.
However, in the case of axis 1, the kinetic energy is the highest possible for a given angular momentum, and in the case of axis 3, the kinetic energy is the lowest possible for a given angular momentum (which can be easily shown from conservation of energy and momentum equations, and is also fairly intuitive from the fact that kinetic energy is proportional to velocity squared, while momentum is proportional to velocity - so in the case of axis 1, the smaller masses will have to be spinning faster for a given momentum, and will thus have more energy, and vice versa for axis 3 where all the masses are spinning: the energy will be lowest). In fact, this is a strict inequality - if the energy is highest possible, there are no other possible combinations of momenta other than L2=L3=0, and vice versa for if the energy is the lowest possible.
Because of this, in the case of axis 1 the energy is so high that there simply aren't any other possible combinations of angular momentum components L1, L2 and L3 - the object would have to lose energy in order to spin differently. And in the case of axis 3, the energy is so low that there likewise is no way for the object to be rotating other than purely around axis 3 - it would have to gain energy. However, there's no such constraint for axis 2, since the energy is somewhere in between the min and max possible. This, together with the centrifugal effects, means that the components of momentum DO change.
Part of this video was sponsored by LastPass, click here to find out more: ve42.co/LP
References:
Prof. Terry Tao's Math Overflow Explanation: ve42.co/Tao
The Twisting Tennis Racket
Ashbaugh, M.S., Chicone, C.C. & Cushman, R.H. J Dyn Diff Equat (1991) 3: 67. doi.org/10.1007/BF01049489
Janibekov’s effect and the laws of mechanics
Petrov, A.G. & Volodin, S.E. Dokl. Phys. (2013) 58: 349. doi.org/10.1134/S102833581308...
Tumbling Asteroids
Prave et al. doi.org/10.1016/j.icarus.2004...
The Exact Computation of the Free Rigid Body Motion and Its Use in Splitting Methods
SIAM J. Sci. Comput., 30(4), 2084-2112
E. Celledoni, F. Fassò, N. Säfström, and A. Zanna
doi.org/10.1137/070704393
Animations by Ivy Tello and Isaac Frame
Special thanks to people who discussed this video with me:
Astronaut Don Pettit
Henry Reich of MinutePhysics
Grant Sanderson of 3blue1brown
Vert Dider (Russian CS-tv channel)
Below is a further discussion by Henry Reich that I think helps summarize why axes 1 and 3 are generally stable while axis 2 is not:
In general, you might imagine that because the object can rotate in a bunch of different directions, the components of energy and momentum could be free to change while keeping the total momentum constant.
However, in the case of axis 1, the kinetic energy is the highest possible for a given angular momentum, and in the case of axis 3, the kinetic energy is the lowest possible for a given angular momentum (which can be easily shown from conservation of energy and momentum equations, and is also fairly intuitive from the fact that kinetic energy is proportional to velocity squared, while momentum is proportional to velocity - so in the case of axis 1, the smaller masses will have to be spinning faster for a given momentum, and will thus have more energy, and vice versa for axis 3 where all the masses are spinning: the energy will be lowest). In fact, this is a strict inequality - if the energy is highest possible, there are no other possible combinations of momenta other than L2=L3=0, and vice versa for if the energy is the lowest possible.
Because of this, in the case of axis 1 the energy is so high that there simply aren't any other possible combinations of angular momentum components L1, L2 and L3 - the object would have to lose energy in order to spin differently. And in the case of axis 3, the energy is so low that there likewise is no way for the object to be rotating other than purely around axis 3 - it would have to gain energy. However, there's no such constraint for axis 2, since the energy is somewhere in between the min and max possible. This, together with the centrifugal effects, means that the components of momentum DO change.
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Komentáře
As a carpenter for over fifty years I've recognized this behavior with flipping of a hammer because I early on decided to teach myself to juggle hammers. I tried to prevent the twist-flip with absolutely no success. It became clear there was more stability in working with the flip instead of against it. This explanation is such a relief! I thought it was a personal curse. Now I realize hammers are the perfect object to demonstrate this motion because they, unlike tennis rackets, have no symmetry about any axis!
Hammers have left/right symmetry
@WPH H clearly none of you have read my comment. I very clearly explained exactly why a bicycle can stay upright without a rider above a certain speed, and why they can be stable at any speed, and ALSO why bikes with different geometries can handle either very similarly or very differently to one another. Wheelbase affects any vehicle, regardless of wheel count. Same with wheel size, and differing wheel sizes front and rear. Bikes are the only vehicles whose handling entirely depends on steering angle, trail, and mass distribution (eg center of gravity, rider lean, and total weight). All other vehicles are affected by all other factors in varying degrees. I'm not just a rider, I'm also a designer. I've dived DEEP into the geometry of bicycles and why and how each bit of the bike contributes to how it handles and I've also researched heavily the physics behind all of it, piece by piece. If you look at the bike as a whole there's no way to truly understand it. Once you break it down to the base components though, it becomes quite easy.
@PH INFO 101 You are correct! I was always fascinated by bicycles and my interest went off the charts after I watched a video demonstrating the fact that a bicycle has, by far, the most numerous amount of variables in tracking its motion when compared to any single, three, four or more wheeled vehicle. It’s the only configuration that is affected by a combination of rake, trail, center of gravity, speed, lean, steering axis, steering angle, wheelbase, wheel size, different front/rear wheel sizes, and a few more that I’m forgetting about.
@Ali Khodajani Thanks for the backup. For some reason, intelligent & ignorant people alike can't comprehend the TRUTH of your comment.
@PH INFO 101 The motion of a bicycle is still one of the unsolved phenomenon in physics .
As a kid, I would frequently watch my dad flipping the TV remote control in his hand and studying the inevitable half-turn in its flight pattern. He concluded that his wrist was subtly imparting spin. If he were alive today, his mind would probably be blown watching this video.
I do this too
@Elgoog this is pretty interesting since most the time when i flip a tennis racket it does the half rotation, but i have flipped it before without the half rotation.
Yes! i always flip tv remotes and thought this as well. Now I know the truth!
🥹
that went from 0 to 100 rather quickly.
I always assumed this happened because I was adding spin without realizing it. The theory of a rotating object trying to minimize its kinetic energy actually makes a lot of sense.
My putting in the additional twist was my presumption as well.
@Elie Kayrouz Yes and we are currently laughing at the irony of this comment.
@Boycott CS-tv Dusty, we’ve already been contacted. We’ve already achieved anti-gravity (thru spin, anti-gravity material… many ways) and we probably can reach the stars and have. I really really seem to ask myself this question more and more: is there a human break-away group that’s jetsetting the stars while we live with Stone Age tools?
A colleague pointed me to this great video! I was fascinated to find that it also contained two additional facts about the great condensed matter physicists of the past century. 1) If you claim that any physical concept is not in the Landau-Lifshitz books, most probably you have not looked for it as carefully as you should. 2) It is really tough to beat Feynman's physical intuition on anything, even if he thought about it for less than half a minute.
Mechanical Engineers found out many years ago that the best approach for dealing with real problems intuitively is to consider inertial forces. Otherwise, you get lost in a massive amount of equations.
enter flywheel effect
Watching a mathematician do something physical and coordinated is almost as interesting as the great info provided.
This explaination is beautiful when you're actually learning this stuff in school... keeps me wanting to know more. Thanks Veritasium!!!
Wait till our earth does this..
Description =/= Explanation.
@Sumo Yes and Our earth proves that in reality, its diameter is larger at the center of its spin. Yet His final conclusion is Incorrect our earth is way out of Balance and it wobbles creating our 4 seasons. and yes our moon helps to keep our wobble in check. except when our moon gets jerked into a More elliptical and Larger Orbit. I'll stop right here. if I say any more I'm sure to be attacked by some
and would spin them on my fingertips
at my work we had handheld scanners and i would always flip those i got good at timing it so i could catch it in any position and my phone
I greatly appreciate all your time and efforts to explain things in a way that make it exciting. I believe I may have an idea. I’m currently attempting to create the idea. It’s a smash up of a lot of things combined to one sir. Thank ya for your time again.
I had always wondered why a tennis racket could never flip straight, finally get an explanation! Thank you lol
This was an incredibly clear and concise overview. Brilliantly done.
It becomes more difficult to travel further in any one axis. Accelerating in one direction of rotation meets this criteria. The wingnut flips because the continuing rotation acts like an acceleration yet with an easy way to change axes from 0 g. The limit as a rational value goes to infinity becomes irrational in the same axis, every time. Nice video!
This was two and a half years ago, and the Riemann Hypothesis is still unsolved. What else could Terry Tao have possibly been working on that was more important than this??? Edit: I just realized... it was the Collatz Conjecture, wasn't it? 😄
I was a dynamicist in the aerospace industry for 43 years, and THAT is the BEST plain text explanation of this behavior I have ever seen! Fantastic!
@Daniel Hope I agree about us inadvertently holding off the next iceage we should be entering or close to entering, I have speculated on that before, but keeping the molten core moving is a good thought i had missed but has potential.
@Daniel Hope also I'm concerned about when the natural iceage cycle ends, I would hope we get our warming controlled before it skyrockets with the normal warming and gives us a new temperature high we're not ready for.
@Daniel Hope Take care in your logic. Which came first. The orientation or the squishing?
@Evan Keal Texas here, so yeah. ;)
The biggest lesson I've learned from getting a PhD in physics is the following: Landau and Lifshitz has *everything* . I was reviewing a paper on plasma physics once where the authors claimed that a certain analytical solution didn't exist -- sure enough L&L had an expression for the exact problem that paper was citing.
@Inscrutable Mungus Thanks I had looked up and I am already on it, Vol 1 Mechanics -Maulertuis Principle. I had already solved Russian physics problem books Irodov and Krotov before. L&L has a similar feel so far and apparently a more comprehensive coverage in all volumes. Thanks 🙏for recommendation.
@Rahul Sharma Look up 'Course of Theoretical Physics' by Landau and Lifschitz (it's a set of 10 books); and 'Classical Electrodynamics' by Jackson. Fair warning: Both are fairly intense reads, but well worth it if you've got the required background.
Can you let me know what books you guys are talking about??
@Dear Green Places My advisor in grad school used to have a flat rule for the group -- we're not allowed to claim that a certain problem doesn't have an analytical solution till we've meticulously gone through L&L and Jackson. I wouldn't be surprised if each of the millennium problems is not buried somewhere as a short example or 'left as an exercise to the reader' in one of the two.
Came to comment the same thing. It was such a red flag when I read that quote I had to pause the video and make a note to check myself.
Have you ever heard of anyone turning one gyroscope inside another, rotating in the opposite direction. So that, when both gyroscopes are in action, the inner one appears to be stationary. Would these counter rotating gyroscopes negate the gyroscopic effect?
I got in trouble at work today because I was tossing various objects and watching the flip. I tried to explain it to the boss but he wasn't having it. He fired me. Now I have more time to watch your videos!
This reminds me a lot of the Wilberforce Pendulum, in which a bouncing up and down motion shifts to a rotating motion and back again, the KE phasing back and forth between the 2 modes. And there's a swinging mode also I think.
Thank you! This is an amazing explanation and I can finally see in my head how it works. I've never been able to follow the maths involved.
I've never been so educated, filled with a learned horror and then so suddenly and gratefully relieved in a single video. You deserve an award for creating the most educational drama in human history.
Wtf
Wow! What a wonderful poetic expression. Has anyone ever put those two words together? I googled it and didn't get any hits. But then I looked at your ID and realized you have a way with words.
@Patrick McLeod 🤣😄😆😐 really?
@Andy Clark The earth bulges out around the equator.
Isn't this just a special case of the butterfly effect?
Im in the middle of a mathematics degree and have taken a few physics courses and I have never felt less confident in my abilities than when he tried to explain the intermediate axis theorem in an “intuitive” way and I still had no idea what he was saying
Fascinating and the maximum moment of inertia appears to apply to your consistent delivery of this long and very clear explanation. It didn't look like you were reading off an autocue either! Anyhow my brain hurts after all that! Maybe the phenomenon should be re-named the wibbly wobbly effect ie the instability of energy transfer. Or why figure skaters don't always fall over when they're spinning.
ive known about this effect since i was a kid. I didn't know what it was called, but I would do this with my tv remote. it fascinated me how it was doing a half twist in the air. i started tossing the remote higher so it would spend more time in the air to get the full twist or even 1.5
Currently working on a linear algebra project and this video provides incredible intuition behind eigenvectors. Thanks!
can you explain how eigen vectors and this is related? I just know eigen vector are used in matrices , don't know their physical significance.
That was a great explanation. when I was a kid I always wondered why flipping a hammer when you caught it was always facing the other way. I once seen a conspiracy theory that was saying the Earth would flip. As man builds large cities we are moving large amounts of rock and steal from spread through out the world to large masses which is changing the balance of the Earth as it spins.
There is also a skateboard trick called the impossible flip because of this. They counter it by leading the front foot trough the flip to keep it from flipping on the other axis.
Rodney Mullen… the guy was a genius
Impossible is done with back foot unless specifically mentioned the front.
That's where my brain went too. Now I'm thinking about kickflips but with an uneven space between the length of the deck.
You made my day!!!!
DID YOU EVER HAVE THE CHANCE TO PLAY MARBLES-
Woah. Yep. I’m wondering what would happen if the earth flipped. Or heck, the sun. Lol :-o Still, even if it isn’t supposed to flip, aren’t the magnetic poles still slowly moving though? Will that affect us? Curious if you could make a video on that. I’d watch that too. Love your videos!
I've noticed that spinning racket phenomenon when I was little, but I convinced myself that it was due to air friction and didn't think further.
My physics professor described this effect using a hammer. With a little practice I discovered I could put just the right amount of torque on the hammer when I flipped it to prevent this effect.
I think i commented about this one a long while ago, i first noticed the phenomenon while flipping a TV remote just like the tennis racket. Great to get some closure :)
Reminds me of the inertial roll coupling experienced by some aircrafts (F100, F102). This was theorized by Philips in 1948, and experienced some years later..
Spent all my teenage years playing with the tv remote, flipping it on the air and noticing the flip. I never asked why I couldn't flip it vertically without it turning. The trick for me was to throw it higher, so it would turn 2 times, so I would catch it how I threw it. Similar with phones when they came around. Then, older I became a bartender for a while and while flipping bottles and stuff (flair bartending) I sometimes noticed the same thing as I would try to get the label to face "forward" when the bottle landed on my hand. You just solved a mini life-long question that I had hahahaha.... kudos! (I was getting a bit judgemental when you mentioned proving Feynman wrong -- "this guy is cocky" hahaha... but then you brought Tao into play and it was all good 🤷🏻♂️😂 -- and anyways, is still a bit cheating as Feynman didn't have all the 3D bells and whistles we have today)
I just spent 10 minutes spinning my remote because of this comment
I noticed this but it's so obvious you're just kicking it off axis, you can't throw something perfectly on one axis in real life, even if you used a machine in ideal conditions.
i am a cook at hu hot, and i notice this when i flip my spatula
You all have what is know among jugglers as the jugglers twitch. You should take up some juggling clubs! You will likely love it! Lots of physics in juggling too! :-)
Same but with my old Winchester skinning knife when I was a kid
That was interesting and really intuitively explained. Thanks!
As I was watching this video I realized these were the forces that cause a tire to need to be dynamically balanced because it's masses are out along its rotational axis.
This guy solves my problems, that I never had. He's simply awesome. 😍 I always learn alot from his every video ❤
I've always tried flipping my badminton and Tabletennis racket this way and got flustered everytime because i couldn't rotate it along a single axis, Now this video explained everything... My sincere Thanks to the random dude in instagram who introduced this video to me.
that was intense ! it's been more than a year probably when I watched the video by the first time and I did not understand much. I'm glad that today I understand more. Thank yo so much for what you do. You are awesome !
Video: contains the phrase "prove Feynman wrong" Also video: doesn't use this phrase as clickbait. I salute you.
@Nickolai M Yeah. It's the same as any other metastable point. It's not a stable solution in reality, as there is always a small disturbance.
@Aditya Saravanan in any real scenario you will always have a disturbance, even if very very small... but in a 3-d simulation on a computer you can have a stable rotation about the intermediate axis because you can model everything "perfect" (no friction, no imperfection in the structure, no slight deflection in the torque that causes the spin, etc.)
@Leonardo de Abreu idk man his students were pretty clever on average...
@fopperer If there's a pun or something then I've missed it.
@Andrew Chapman dude, you dont get it, do you...
I've always done this with a hammer, or large crescent wrenches, and wondered why it would flip around the handle axis.
Really professionally put together video. Excellent.
Man, these animations are always top notch.
Even as an experienced mechanical engineer, I am amazed at what I don't know. Thanks for this,
Wow, I've always noticed this and while I wasn't confused with how it happens or why or anything, it just confused me whenever I tossed something in the air and caught it the other way.
I've been flipping tennis rackets for years and never been able to get my head around this effect. Incredible.
@RonRon Yes, hammers, too! I tend to be a bit more mindful of my toes and such when flipping hammers, though. :)
FXM I ‘ve been doing the same with hammers.
@FXM i love this
SAME I LOVE THIS I LOVE THIS
same dude, same. Crazy how you experience it without knowing lol
I remember years ago, there was a commercial for I believe it was, the Red Cross and being prepared for any emergency. It had a disaster, where the whole earth turned upsidedown and the family walked out of the house and we're then standing on the roof that was now the floor. It had me seriously thinking they were warning us to prepare for something.
So going back to Tao’s explanation, what happens if Y axis is not tilted, what if we are able to flip it from a perfect level position?
This video actually helped my tremendously in my physics class on angular momentum and torque lol
I have a 3.2 gpa from HS so I’m not altogether stupid, and to my defense that was about 50 years ago before grade inflation was a big thing. But in the interest of disclosure most of my HS was spent in vocational tech where just showing up would earn you an average grade of 2.0. My 3-hour auto shop class in my senior year was used to fulfill, somehow, a needed math credit. So as interesting as this CS-tv is, what I find really startling is at 5:26. (It actually happens in the first part of the CS-tv but I didn’t really understand what I was seeing on first viewing)m.) The doodad that is spinning is “falling” upward. This is inside a space vehicle, right? It’s a weightless environment, right? Disregarding the cute little flip, the rotational movement along a helical plane of the thing should push it straight out of the hole. The center-axis (did I use that term correctly?) of the doodad should stay in line with the center-axis of the hole from which it unscrewed itself. But as I watch the CS-tv it is moving toward the upper border of the image. This could be an optical illusion. The motion could be relative. Maybe the hole is moving down, so the upward movement of the doodad is illusory. But if momentum is conserved (I’m told that is why when I jump straight up the earth, moving at 1000 mph, doesn’t spin underneath me) and if (but for the thrusters keeping it in orbit) that space ship and everything in it is all falling toward earth uniformly why does that doodad appear to move differently relative to the hole from which it was unscrewed?
As a skateboarder who flips things daily, this is very interesting!
I noticed this years ago flipping a hammer in the air. Each time the head points a different direction. It's cool to have it explained.
Did it ever get stuck in your eye!
Veritasium argued, correctly, that the flipping happens as a consequence of the rotating body trying to minimize its kinetic energy. This is a more profound statement than it appears. The minimization principle applies to unexpected situations. For example, Donald Trump rose as a consequence of Americans trying to minimize their intelligence.
@Vary More than ONE thing in just one hand? Where was the other hand???
"Excess to requirement". Please explain what you mean by that?
I used to be obsessed with flipping my framing hammer at work doing tricks and stuff, and one time I just did a single flip and the head stayed on the same side. I’ve never been able to do it since.
I was dancing to 80s music a while ago and I have done a few spin moves and then I thought of something philosophically unconventional but, I thought that Rotational Motion was sacred and I was a bit surprised to even think about it. Then I started to think about car engines for some reason after. Now I’m watching this haha.
Wow, this was a very interesting video explaining object behavior. I'm going to watch this again.
I almost didn’t watch this one but then I remembered that it’s impossible for veritasium to have bad content
Totally fascinating. I believe the Oumuamua was also flipping over longitudinally.
I use this property of rotation in fire dance and never once thought about why it works. So cool!
I first observed this phonomenon 54 years ago when I was juggling books, as one does, especially at age 10. I asked again and again over the years what caused it. My parents, teachers, anyone who'd listen, No one ever had a answer. Most had never noticed it happening at all. I'm sure knife throwers must have figured how to predict it even if they didn't know the cause . Well. thanks to Veritasium, if finally got my answer last year, in 2019. 🖖
I observed the phenomenon about 45 years ago, flipping a hammer. Not holding it head-down, as to strike a nail, but with the head pointing left and the claw on the right. Every time I flipped it, the head and claw reversed positions. I was amazed. Now I know there's a name for this oddity.
@Hype Hype Of whom were you enquiring ? Or perhaps we could ALL respond ... Eighteen biographies later ... 😉
Can i ask what you do for a living? As most kids don't ask such questions.
should have gone into physics or mathematics XD
@GrowBetter True, reverse one or the other, but seems easiest to reverse the first stage than the more complicated wrap 2nd stage. I forgot to mention above, that I learned that via @Mathologer who did a vid. on optimal lacing which led to a site (friend of his?) that amongst a million other things pointed out the correct way to tie ones shoes...
I watched Rodney mullen doing a Ted talk about the physics of the "impossible" skateboard trick and it's basically this principal here it's cool he's so interested in the physics of his hobby/career
Really nice Mechanics 'lecture'! Would Earth's rotation be affected somewhat by continents shifting as a result of plate tectonics?
I was not aware of this though I have the same ring on my little finger as you have. Regarding the “centrifugal force indicated by arrows” may miss lead some. I always refer to tangent directional arrows as the “ manifestation” of the centrifugal force, as we all know that there are no centrifugal force, only the force which is retaining object in a circular path. I love your shows, very educational though I loose you in math pretty soon. I am very old but this is no excuse. Keep it up, something among the few it worse while to watch.
So this is what happens whenever I flip the remote and it does a half spin
Yeah 😆
Awesome video, really instructive. However, I think there’s a small mistake when it shows the images of the earth twisting (at time 10:09 - 10:18). I have a problem that I’d like to bring to your attention: the absolute direction of the earth rotation changes, whereas it should remain the same (to conserve angular momentum), only the poles should be inverted. What I mean is that, should such an event happen to the earth, we should see the sun rising in the west, whereas the images of the earth after the twist show the sun still rising in the east.
To be fair, it would be much easier to have a simple 180 degree rotation of an image of the earth, rather than a rotation of a fully lit model of the earth with realtime sunlight. Easier for video production, but not as accurate to reality. Still would be cool to see a fully rendered simulation though
@qqqqq537 🤦♂️
@qqqqq537 Sun has always rose from the East, ever since the quran was written. Did you mean "sun rising from the west"?
This experiment is represented in a humorous way in Kerbal Space Program. When in mid air or a vacuum, while EVA, you can perform an experiment where the Kerbal tries to spin a wingnut, but he spins instead. It's not exactly the same thing, but it's really cool to finally learn from where they drew the inspiration for that animation.
Did that change? When I played it did this, maybe it’s based on specialty
lol that's awesome
"The strangest thing is not that it happens, but that spacecraft works without this part"
Another KSP fan.
Excellent video! I would just add another schematic video of the disk, bit with four equal masses, with an explanation on why ot wouldn't flip.
This is very close to what I want to know. With uneven masses still, while rotating about the first axis, the large masses are t moving. But if it is jostled ever so slightly off axis, the large masses should experience some centrifugal force causing them to move further away from the axis. I understand in a rigid body, they can't dissipate the kinetic energy, but that doesn't explain how they avoid the centrifugal force pulling them outward. For equal mass objects. The same question arises, but I think it doesn't matter so much whether it flips or not because I think flipping is akin to Derek's flying disk just rotating, so you wouldn't even be able to tell unless you mark the disk and watch where the mark ends up. It wouldn't change the moment of inertia at all. However, he also says that the heavier masses (having much more inertia) basically force the smaller masses to stay in the same plane as they flip. But that wouldn't necessarily happen if all the masses were equal.
When I took physics in the 1980s this one of the demonstrations. The lecturer did it with a book. Rotate it about an axis parallel to the cover or to the shortest edge of the book and it rotates in a sable fashion. Rotate it about the other axis and it flips around in multiple axes. (In your video as soon as you said it was a new phenomenon I thought BS right away.) EDIT: And there it is at 11:10 although I'm disappointed you didn't show the other axis.
The "bolt in space" system is a totally different system than the other ones you mention. In the first system there are only two states of equilibrium, which continue for a terrifyingly accurate time span say X secs or rotations in direction a then X sec or rotations in b. It seems that once a variable measured from a point on the bolt (say the moment/k.e./precession of right end of the screw etc.) slowly increases and reaches a certain value of n, the state of the system perfectly changes from s1 to s2. The same process repeats itself and this time system changes from s2 back to s1.The variable as well as the whole system direction oscillates perfectly in two states forever (a nice sinus wave with sharp ends). A perfect "reset" back to identical initial conditions occurs. Much has to be investigated here. The systems discussed here are very different. It is like comparing apples and oranges. The video doesn't simplify the matter. It just complicates it. How shall we define the bolt in space behavior? (a dual state periodically self-resetting system?) What types of weight distributions result in this behavior in space/under zero gravity conditions (again a constant of the bolt in space system, things don't behave like this on earth)? See Milankovitch cycles for tackling this via a better video. It took him 30 some years to find what he found. Also kindly add a simulation and the graphs of the changes in K.E./moment/precession or whatever variable just jump starts at one edge of the system let's say (ie. using motion capture-position data from sensors placed on (and in?) various points on (and in?) the bolt, do velocity/k.e./momentum calculations using this data). I am sure (that is 100% sureness), if there are asteroids or even planets, that have a center of gravity distribution mimicing that of the bolt or bolt in clay model (and that weight distribution doesn't change for a certain amount of time), they must be exhibiting the same behavior. The earth? I am not sure, but there might be a certain "configuration" (weight distribution let's say) if kept constant for enough rotations, that will push earth to behave as the bolt in space as well (enough skyscapers on one side? (joke) A huge tectonic/magma shift, then just 40 days of rotations? Or maybe miniscule but steady changes of weight distribution spanning a couple of million years? (precession at its limits) How about a video on scenarios that would make earth behave as the bolt in space?) P. S. Feynman is overrated.
Erkin..i like your post. However, I really doubt mankind could shift enough material on earths surface to change our axis. We are still tiny ants compared to earths mass.
Noticed this years ago while throwing knives. Never understood it. Thanks for the video!
@Veritasium. This was very enlightening. As an Electrical Engineer, I spend my time understanding the intangible. I’d really love to have a discussion about this topic and the history of Earth and global warming solely focused on the potentials of this science.
I'm a carpenter and I'm constantly flipping my hammer while I'm not busy. I've wondered for the past 10 years (I became a carpenter in 2010) why is it the head and claws of my hammer flip flop when I flip my hammer head over handle. I thank you for this video!! I suffer from ADD/ADHD and I find myself pondering this very often (driving myself nuts over it). Thanks again for the answers!!!!
Yes.. im not a carpenter but im always flipping object over. The hammer does it perfectly :)
I also did the same with my hammers ... ... in an engineering workshop. Its interesting that the change in direction only occurs ONCE in each flip. But if you get better at flipping your hammer, i.e. let it flip twice before catching it you'll find it does the hammer-head change of direction twice, allowing you to catch it in its original position. However; in years of doing this (I can flip it and catch it without looking at the hammer .. .. as long as it is within peripheral vision), I thought this phenomenon was to do with the way we let go of the hammer. We are not robots, so (I think) a close inspection would reveal that our hand releases on small surface of the handle before another part is released. Based on that theory, I can flip my hammers WITHOUT the "tennis racket effect" taking place. Any comment on this from the video maker/presenter?
@big6pun07 lol, there's alot of us!
Hi, I'm also in the hammer flipper society. Drive me nuts for years!
@Chuck Roast me too, I'm a hammer flipper, thought I was the only one who noticed. Lol
When I saw it I thought: It would be incredibly difficult to spin something perfectly on one axis
I always throw my phone in this way and it always flips over. So cool to have an explanation
Nice video! You should consider doing a video dedicated to why we have or think we have magnetic pole shifts on the earth
Hi, Derek! Thanks for bringing this subject to light. Let me get this straight. There are infinite axis by which you can spin an object, right? When you mention the object's "three principal axis", I think there are only two that you can clearly point it out: the ones with the greatest and the smallest moments of inertia. All other axis of rotation (infinite possibilities) would result to be in an intermediate moment of inertia. Is that right? So, here is a first conclusion: the stability of a rotating body is as higher as it is close to one of those two main axis (with greatest or smallest moments of inertia). Any rotation in an axis that has the slightest difference from these two would result to be an unstable one, and the body would flip after some time doing more or less spinnings (depending on how close it is to one of those stable axis). Am I correct to think of it this way? And, if so, here is another thought: when spinning the tennis racket by hand, we problably cannot reach the precision to do it exactly in one of those two main axis. And maybe it would flip if we gave it enough time to make a lot of spinnings. Which brings me to this: thinking the Earth as a body in constant changes (we have a lot of heat and pressure underneath our feet, evidenced by volcanic eruptions and earthquakes, not to mention external factors that might ruin any stable movement), what are the odds that our planet is really rotating in a stable axis? It makes me wonder, since there are a lot of cultures that talk about cataclysmic events that occur from time to time. And we have a bunch of evidences of it. But let's leave this conversation for another time. For now, for those who is interested (and also the skepticals), just reasearch about a book called "The Adam and Eve Story" and ask yourselves why it has been classified by the CIA in the 1960's, and has not been fully declassified by the Freedom of Information Act. I don't mean to be conspiratorial, but to me it's clear that this knowledge has been around for some time (like "always"), and is held by only a group of people.
Interesting. I guess that's why in skateboarding we call similar trick "Impossible". But of course it's possible cuz with the help of your feet you wrap around the skateboard so you prevent it from flipping.
My question after watching this, though, is "How much mass would we need to dump at the poles to make the earth flip 90 degrees?"
I love how this comment started a physics debate
@Jacob Thomas He's talking about the kind of flipping exhibited by the fluid filled cylinder that has two principle moments of inertia like earth
@Asag no, both are incorrect. Freeze a kilogram of water. It weights the same. Ice is less dense than water. 🙄
@Sir AaronWe want the current axis (south pole to north pole) to flip, right now this axis has the largest moment of inertia because the smallest moment of inertia is when the distance of mass from the axis is the smallest. The radius from the centre of Earth to any point on the equator is bigger than to the poles (that makes the current axis the axis with the largest moment of inertia). For the Earth to flip we want the axis that we're spinning around to become the one with the smallest moment of inertia. So we have to make the radius from the centre of the Earth to any given point on the equator smaller than from the centre to the north/south pole. To do that, we have to transfer the mass from the equator to the poles so we basically flip the geoid of Earth and the axies will stabilise after some time which means flipping the Earth.
@Kyle Wells this is a really good point actually. The kind of flipping in this video could never happen to the earth naturally because of the molten core. So the question is almost a two parter: how much mass would you have to dump at the equator to initiate the flip rotation plus how much mass would you have to add to that to compensate for the natural redistribute while the flip was still happening. It's probably at least more mass than the moon
Why isn't the explanation for the intermediate (y)-axis in 8:28 not equally valid for the x-axis. A small inclination from it should give the same periodically movement in my view, the only difference is that now the mass ratio between the main rotating mass and the tilted is different... Any ideas about that? I would appreciate it :D
Whoa! That's trippy! My brain has so many hurdles to get over before it can understand this. Like, in the tennis racket example, isn't the moment of inertia the same for the 2nd and the 3rd axis?
Hammers, drills, wrenches almost all my tools at work have three principal Axis lol. I've learned how to throw most of them in smooth circles but it takes a thumb or wrist motion to keep everything on two axis. I'm still yet to learn how to catch 10mm sockets though.
I watched this video (or at least part of it) about 6 months ago. This morning I started jotting down some ideas I had related to this concept. I started watching this video again while writing so I could get the terminology correct. I'm going to copy and paste what I wrote here and would love any feedback: Intermediate Axis Theory to explain the Earth’s reversing magnetic field. The following are my thoughts, inspired by the CS-tv video on the channel Veritasium entitled The Vizarre Behavior of Rotating Bodies. The video describes the 3 principal axes of a mass: 1st axis has the smallest moment of inertia, 3rd axis has the greatest moment of inertia, and the 2nd axis (the intermediate axis) has a moment of inertia between the first and second. Imagine the Earth’s inner solid core is spinning in what essentially is zero gravity. Because the mass of the earth somewhat equally surrounds the inner core, the gravitational forces cancel each other out. The inner core is surrounded by (suspended in) the liquid core. Suppose the inner core in not perfectly spherical and has an intermediate axis. The intermediate axis theorem, based on The Twisting Tennis Racket as published in the Journal of Dynamics and Differential Equations, Vol. 3. No. 1, 1991 and possibly the Russian discovery by Cosmonaut Vladimir Dzhanibekov while removing a wingnut in a failing space station, is summarized as follows: A body that has 3 unequal axes will spin with stability about its first and third axes, but spinning about its second, or intermediate axis, will cause it to flip 180 degrees about that intermediate axis. I don’t have the physics knowledge to explain any of this, these are just my thoughts. My Theory is that the inner core of the Earth has 3 unequal axes and is spinning about its intermediate axis. I remember some things from my days at Purdue University, many years ago, and one of those things is the involvement of the Reynolds number when scaling experiments. That is really the total of what I remember about the Reynolds number, but basically it means that I have no way to contemplate modeling this. I am re-watching the above-referenced video and I either didn’t watch it long enough the first time (about months ago) or blocked out a part of the video, but the part that just played is explaining what I just started trying to explain. I just finished the video, and there is a difference between what I started to write and what was just explained. The video concluded that the Earth as a whole must be spinning about it’s 3rd axis, but didn’t consider the solid inner core within the liquid outer core.
Interesting. I work in kitchens as a chef, and one of the fun games we play is to try and spin tongs without the 1st axial twist occurring. As far as I understand, kitchen tongs have the same three axes as a tennis racket. And yet I have been able to spin them only on the 2nd axis. In fact, pretty much everyone who has played this game in the kitchen with me has been able to achieve a clean toss after just a few tries. What could be going on for me to be able to do this?
How about adding thermal energy into the experiment. Try lobbing a saucepan of smoking oil into the air - and then add the kinetic energy of running away - quickly!
I thought the reason the Russians kept this a secret was going to be so their female gymnasts would always win gold!
😂❤
Lol
@Giancarlo Vadalà look at the damn tennis racket
@veritasium One very interesting question was not answered - why flips occurs regularly? And what’s the force, that disturbs balance and force to flip object by intermediate axis?
Fascinating! I love this stuff...as long as I’m not required to know it or be tested on it! 😂
What about plate tectonics? As the crust is dragged under, and redistributed is there a chance that the maximum moment of inertia of the could be changed by this redistribution?
I had seen a video on this subject awhile back and today I heard something about it and it turned on the lightbulb. I searched for a video of this happening and wrote in the comments: "I know why they do this, and it is a lot more simple than it looks!! To figure it out, all you have to do it watch the ending half of this when the handle spins slowly enough that you can play in slow motion and see the moment of change. It is a balance issue from material being removed to add in a set screw location for the handle. That small imbalance is enough to cause the flip every few rotations due to build up of imbalance. The handle part of the T handle doesn't play a role in inducing the "dancing" effect." Then realized it wasn't even a science channel and wanted to put this somewhere that others would read it instead of readers just being awe struck with the video alone and ignoring the how and what is going on.
Thanks this is super interesting. It brings to mind the recent discoveries of the massive blobs of higher density that's been found inside the earth. Its thought that these have higher density than other parts and if you look at some 3d maps you'll see that they support these rotation theories as the blobs are centered along earths 'mid riff' so could possibly be the factor deciding earths orientation.
Like the stability-bar on top of the top rotor of an RC helicopter.
"Babe, come over, im home alone" "No, babe, Im solvin a centuries old math problem."
@ Andy Goins Travel in an airplane or travel on the ocean in a boat. If your eyes work, there's your proof that the earth is indeed a round, globe form. Humans figured this out 2nd century BC. Case closed.
@Andy Goins If I put as much research into it as you did that would amount to a research time of zero. Since I already have done quite a bit of research before during my lifetime, I now would have to do a negative amount of research time to reach your level which is physically impossible.
@Andy Goins counter question: why would inteligent teachers tell us the earth is a globe if it was flat? Why would the NASA make "fake" pictures of the earth. I couldn't seem to find any reliable sources that prove the earth is flat, mind sharing yours?
I'm Chris Hansen....why don't you have a seat.
She's never moving out, is she
Could a tectonic shift, albeit likely through a long period of time but ultimately happening in a moment, alter the mass of the earth enough to change the intermediary vector and cause a total rotation?
Well this explains a neat thing I've played with for years. Grab a thumbtack by the pointy part and spin it on its curved top. It flips up onto the edge and back again.
I've been doing this with ball peen hammers for 30 years. When you flip the handle around the side profile of the head (like the tennis racket) it changes direction.
So if you spin perfectly the tennis racket, will it flip ? I mean, as I understood that circle explanation, flip is due to a little deviation from the plan. Does this mean that if there is no deviation (perfectly axed spin) there is no flip ?
I was (perversely) thrilled to see you included the link to Janibekov’s paper. 👍 But clicking it i see they ask $39 for the paper. And, frankly, I haven’t yet bought breakfast… 👎
This phenomenon fascinated me as a 10 year old since I’ve been obsessed with skateboarding, (specifically flip tricks); and although I could not explain it, it was what first got me interested in physics.
I’m kind of surprised there aren’t more pro skaters who like physics, it makes logical sense haha
@Bradley Ries the impossible is my favorite trick and i think tony hawk did a video about this physics property
it expains why my 360 flips always ended up upside down :-D
Interesting point! Kickflips and shuv-its are common tricks, yet the impossible is well....harder to do!
Do you see the optical illusion happening in some of your animated graphics? At about 727 into the video, the disk on y axis suddenly flipped. Instantly. Even as the arrows appeared and lengthened. Then I was able to back to that to try to see it both ways with concentration, not even sure which way it is supposed to be going. I let the video go on and saw that in later parts, where they transitioned but still with them going and transitioning this way or that way. When I first saw this at 727, I thought that was without it transitioning to another rotation or axis with that detail about to be added and explained. But this is the diagrams seen either way. Check it, let me know what you think.
We are measuring healthy levels of veritasium in these episodes
Is it possible to spin a sphere on all 3 axis at the same time with the same amount of rotation? if so, what would be the path of a single point on the surface of the sphere through space?
What about this? Some weeks ago I discovered if you suspend a sphere - or apple - on a string - it will start wobbling and then begin to spin quite fast for as long as it can before the suspension string twists up on itself and causes an opposite torque. I need to find a frictionless coupling which would prevent the string from twisting up and see if the sphere continues to rotate indefinitely. Perpetual motion?!
I noticed this effect when I was a little kid flipping my tv remote out of boredom. I figured out, no matter how I tried, that I couldn't flip the remote with it twisting as well.
As a career military pilot with a BSC in Aero Eng the word Lomcovák comes into my feeble brain. Especially after a bottle of vino!!!
Someone should tell the Flat Earthers of the Dzhanibekov Effect. They'll freak out and think that sooner or later their precious disc world will flip and they'll all fall off.
I finally managed to find this absolutely legendary argument after a year-ish
@DutchObserver a collection of different size disks could make a sphere
@Robert Rudd bruh I'm convinced you're just trolling or was dropped on your head as a kid
Settle down nerds!!!
Thank u veritasium, very nicely explained 👌
Your video brings to mind Golf. Our hands and wrists have three axis as does all golf clubs. When it comes to swinging a club our rotating body is the centrifuge that swings the club on it centripetal path All golf clubs are designed to swing on an intermediate axis as they reaches the bottom of their arc at the ball. So if golfers were to permit all this to happen they all would be much happier. At age 75 I finally learned to simply fold my trail arm and swing my club and wow the difference it made in my game. Cheers
The smaller pair of cubes, if you were to trace their outlines, appear to create a pair of identical, yet mirrored, Morlet wavelets.