This String Shooter Is SO Weird

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I love string shooters because they behave so counterintuitively. I was able to get hold of this prototype and make a few modifications to try and explain why the string does what it does!
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[@SteveMould]

I really want to try a string shooter with variable speed because I think there will be some interesting behaviour at the boundary of instability! Maybe I can modify this one... You can also discuss this video on REDDIT: stvmld.com/7htxvr_f The sponsor is KiwiCo: Get your first month free here: kiwico.com/stevemould

[@saifmohammed9070]

First

[@alexlexo59]

2rd

[@DennisXiloj]

Second

[@bigsteve6729]

Just put a potentiometer between it and the power source

[@CarlVardeman]

A high speed camera (Ala The Slo Mo Guys) might also be interesting to show the behavior immediately after various disturbances. Our perception of the disturbance at real time might be different from what a high speed camera catches.

[@YeanyScience]

Hi Steve, thank you for kind words for my video and suggesting my channel This piece has been one of my favorites for years and also one of the most baffling. A far simpler analogy that I like to use to describe the wave movement is somewhat like a throwing a rock in a pond and seeing the waves move out in all directions at the same speed. Now try throwing a rock in a moving stream and the waves moving down stream will move very quickly and the waves going upstream tend to move very slowly. This suggests that at some point where string speed and the wave speed match there would be no wave moving through it. I have a similar piece that produces slow moving waves through hanging string, ribbons, or chains ( 2 videos on this are on my channel) I can easily vary the speed on these pieces and it's much easier to observe the speed of the wave changing as the speed of the chain changes, also fascinating as to how rigid the chain becomes or string on the opposing side. However I have not been able to match the chain speed and wave speed to get a standing wave where I thought it would have. I suspect that as the speed increases the tension increases enough to keep this from occurring (I'll have to get a faster drill and try it again). Another interesting note, is that the string flies due to lift created by drag as it moves through the air (studies have shown this doesn't work in a vacuum). I used to build these and sell them and we noticed that the old worn string fly better than newly made strings. We found that by rubbing new string with sandpaper, little hairs form on the string surface increasing the drag force, thus allowing for longer loops, my longest loop is about 20 feet of string. I do have some additional thought on the string's strange behavior and hope to share more on it in a future video.

[@domenicobianchi8]

Nice, hope to see a collab for part 2

[@marc3542]

The wave on a moving stream was easier to understand for me. Thanks a lot for this comment.

[@SteveMould]

Really interesting! About the wave speed matching thing, it's interesting that the *average* wave speed seems to match the string speed (a little slower on the pushing side and a little faster on the pulling side). It makes me think that you're never going to get it to match, no matter the speed of the dtill, but I'd love to see an attempt. Will definitely experiment with varying the speed on the zipstring. And very interesting about drag.

[@MatthewStauffer]

@@SteveMould This is your guy! Do another explorative knowledge collaboration with Bruce!

[@sonnenklang6925]

The waves in a pond move actually not all in the same speed because of dispersion of the pulse, also if you look very carefully at some wave group it looks like the individual waves are faster then the group and seem to roll in at the inner edge and dissapear at the outer edge of the moving packet ..:) (Solitons and Solitary waves are another Story for sure ;)

[@MedlifeCrisis]

Brilliant. But I’ve got all the way to the sponsor read and not a single String Theory gag. I’m not angry, I’m just disappointed.

[@SteveMould]

It's after the sponsor read

[@JinKee]

@@SteveMould it’s just a theory, A STRING THEORY aaaand CUT

[@BeeKisses]

Yeah, Steve? Don't bait medlife into the next beef, you're not winning that one.

[@morkovija]

Mould string theory - you heard it here first folks! Now with whom should we start a new beef though?

[@SmashedHatProject]

it's because this is String Practice

[@Nighthawkinlight]

Bruce Yeany is a treasure. Also I can't believe that opening clip is real. I've wanted a string thing for a while myself. I had forgotten about it.

[@DavidvanDeijk]

so happy to hear this shoutout, really made me smile

[@2.7petabytes]

Agreed!! As a matter of fact, I would posit that Steve! Bruce and your channels are ALL treasures! 👍

[@jankcitycustoms]

so much cool stuff out there, just isn't enough time for it all.

[@justpaulo]

With a bit of luck this could well be the new fidget spinner...

[@cleanlens]

sure monke

[@petersmythe6462]

Reminds me of the idea of an active support structure like a space fountain or orbital ring. It's particularly interesting that it has such incredible stiffness.

[@ilikaplayhopscotch]

I used to think my cat was real stupid for finding such entertainment in a piece of string, but then here I am, wanting to buy one of these.

[@shannon1267]

Our cats have been trying to discern this the entire time

[@goldentortoisebeetle9741]

If cats could speak they would illuminate us with many insights about string dynamical properties.

[@jaywaghthegreat]

This, this is the comment that the internet was made for 💯

[@piotrarturklos]

The secret cat court is now debating whether to punish you for your past arrogance by ordering a soiling all shoes you will ever have.

[@JohnDlugosz]

I worked for a small company where the software engineering offices was a small enclosed room built inside a large warehouse space. One day the owner comes by to find all the engineers (including machine and EE) gathered around watching the door close via a automatic closing gadget attached to the top. It would start to accelerate, as you would expect from any spring, but then slow down suddenly as if damped, but then _reverse direction_ briefly, slowly, before closing the rest of the way.

[@toshley6192]

When you pivot around the handle, the far end of the string has to travel along a much longer arc than the handle does. The string itself isnt rigid so the small force you apply to move the handle a few inches can only move the far end of the string an equal distance in the same amount of time, it takes more time for the far end of the string to complete its arc ater you stop rotating by reacting against your now stationary hand. When you move in a straight line from left to right the near and far ends of the string are travelling the same distance. Not sure if thats actually the reason, but it makes sense intuitively. You can also consider how a slack line would behave if you held it in your hand and rotated. The far end of the line would only be moved by an amount equal to the distance your hand travelled. The more i think about this the more complex it gets. The string is experiencing a centrifugul force thats perpindicular to the rotational force you apply when you rotate the handle, theres gyroscopic procession involved, possibly some sort of mechanical advantage, the role that the speed of the string has on the propogation of waves...

[@shookings]

I'm beginning to think that you just want as many scientific papers as possible to mention a "Mould effect"

[@SteveMould]

Could be, could be

[@avesh_sayyed]

@@SteveMould omega lol

[@catmadeofdog]

Steve’s out here pumping up his h-index like it’s nothing. Researchers hate this special trick!

[@russellwarren9595]

i am just waiting for the day that Steve discovers a fungus that can be used for making fancy blancmange or jelly castings.

[@babylonfive]

@@russellwarren9595 Or if he figures out certain characteristics of tooling in plastics manufacture?

[@MrNicePotato]

I think you can colour a part of the string so that you can keep track of the string speed compared with the wave speed. Also, I think it would be an interesting wave equation to solve with periodic boundary conditions and setting a moving 0 displacement point where the rollers are.

[@brandongaines1731]

I wondered about the string color, as the photos of the StringThing showed a variegated string

[@ZipStringOfficial]

We just saw your video! What a great explanation! ZipString on a drill was so cool. Love seeing others use creative ways to solve a problem🔥🔥🔥

[@AtomMan523]

What an amazing device. I felt the same as Steve when I saw it - I have to have one! Just submitted my ZipString pre-order a few minutes ago. 🙂

[@timfromkerncountyca2006]

Every thinking person needs a String Thing!

[@Jamesvandaele]

And just like that, a zillion pre orders appear.

[@Vicus_of_Utrecht]

​@@Jamesvandaelethe company went defunct and all the employees unalived 😮

[@makcatchem9614]

I have so much respect for this KZbin channel not only does he do informational informative and great content with science. But he also gives full credit where credit is due and that you don't see very much and I appreciate that in a channel

[@jasonkrise495]

So instead of attaching the sting shooter to a drill, what if you connected it to a speaker and played different tones? What patterns would the tubes impart in the string?

[@SteveMould]

I tried that actually but the amplitude was just too low. Need something else I think. Maybe a jig saw.

[@DavidLindes]

@@SteveMould Oh wow. Please!

[@Abcdefg25152]

@@SteveMould ofcourse you tried it

[@nagriffin3561]

@@SteveMould Your speakers weren't powerful enough. No... it doesnt matter how big your current speakers are, you need bigger ones.

[@bvoyelr]

@@nagriffin3561 I think Mark Rober made a megaphone that might fit the bill.

[@ericgoldman7533]

It seems to me that we've forgotten to account for the difference between linear displacement and angular displacement when trying to explain the behavior. When you move or rotate the device, you impart a discrete change in velocity to each discrete part of the loop. To simplify things, we will make a few assertions- 1. Our side-to-side movement is at a constant velocity, and our rotation is at a constant rate. 2. Our acceleration is applied in a single discrete unit of time. In other words, the velocity instantly changes from 0 to the final value. 2. The displacement is propagated to all points in the loop quick enough that we will consider it instantaneous. In the case of linear displacement, the same velocity (in both magnitude and direction) is applied along all parts of the loop. As a result the entire loop moves together with the source (i.e. the device). In the case of angular displacement, all points along the loop move through arcs of equal length (since we are still applying the same change in linear speed to each point), but arcs farther away from the source radially will sweep through smaller angles, thus causing the loop to appear to curve. It is also worth noting that there is probably some interesting relationship between the forces that cause the loop the hold its shape, and the torque applied to rotate it about the device. I suspect we could see some interesting phenomenon by tweaking both the rate at which the device "generates" the loop, and the rate at which we rotate it about the device.

[@AtomicShrimp]

The sideways movement vs turning thing does seem quite gyroscope-y; if it was a solid ring of material that you were rotating in front of you, it would behave like the disc of a gyroscope - resisting its axis being turned, but not resisting movement along its axis. The resistance to turning is, I think, the same thing that manifests the effect of the furthest part appearing to move in unison with the nearest part - if it didn't do that, it would require turning the axis of rotation. However, I was wrong about the chain fountain thing, so... pinch of salt and all that.

[@wildcodefox7313]

Ayy didn't expect to see you here atomic

[@peacefroglorax875]

Could it be just a maximum propagation speed? Like, if he moved side to side really fast, would the end of the string thing show the same lag? Because when you rotate, the outside edge has to move really fast compared to the inside portion.

[@cleanlens]

shrimps are great

[@bubblinebee]

@@peacefroglorax875 ^ this

[@Josh729J]

thats because its self correcting like a bicycle

[@pligon09]

This is what I love about the KZbin science community; the rivalries are entirely friendly in the spirit of discovery, everyone supports each other and promotes great content and genuinely wants every other content creator to succeed and build off of each other, causing all of us to go down this rabbit hole of real science from what started as essentially a school demonstration. Bravo everyone involved

[@shottysteve]

im gonna be honest i didnt understand a single thing u said but i watched the whole thing to see u play with the string thing

[@ricardoreyes9470]

didnt we all?

[@ethanm3842]

Glad to see you're not dead shottysteve

[@GreenFox1505]

Are you a cat?

[@FrostedSapling]

*zipstring

[@cleanlens]

monke?

[@MattBlytheTheOne]

When in motion the string is exerting a force (using energy) to leave the loop and the resistance of the string is greater so the loop is maintained in a centrifugal wave a bit like gyroscope but more significantly, like a flywheel. When you move sideways you are maintaining the axis of the flywheel which generates negligible turning force. When you pivot the handle around it’s axis you introduce a new flywheel that opposes the existing flywheel. The time it takes for the pre-existing flywheel to dissipate and catch up with the new flywheel is not instantaneous because the loop is flexible. Since the loop is an affect and the motor is the cause, the affect must fall in line with the direction of the cause and re-establish equilibrium. If the flywheel were fixed like a sold piece of metal, when you pivoted your would experience measurable resistance from the flywheel. The energy of the resistance has to go somewhere and if moved fast enough, tends to want to move upwards... sufficient is the upward force away from the fixed point, that it will overcome gravity. I think you wave theory is correct btw and is affected by the tension of the string in the flywheel. Like a guitar: the tighter the string, the higher frequency the wave and shorter duration of vibration... String theory lol.

[@ku3kyc]

Being able to vary the roller speed will help explain the wave speed "doppler" effect better. If you could slow it enough and still have a loop, the wave may propagate both ways.

[@ikitclaw7146]

Would be a simple setup if he has some way to control the power going in, its jst 2 small electric motors, less power less speed.

[@maxthexpfarmer3957]

He could also use strings of different densities and cross-sectional areas.

[@TlalocTemporal]

@@ikitclaw7146 -- I would think it's just one motor, with the rollers geared together. Two motors would tend to run at different speeds, especially with wear, and would also be more expensive.

[@ZM1306]

​@TlalocTemporal I figured one motor and one idler. You just want to have adjustable pressure or spring-loaded tension on the idler. Think of the feed mechanism on a "mig" welder

[@Bound4Earth]

String shooters are one of the best rave toys. dance along to the beat with the string is so much fun and other people love watching it just as much. Loop Lasso and Zip String are now for sale on Amazon and elsewhere.

[@erbro]

Actually, I was taught that this effect and the gyroscope are the same effect, but in the other order. The gyroscope is much easier to onderstand is you first make one from a chain, connected to a hub by a number of strings, a bit like a bicycle wheel. When you try to change the direction of that while it is spinning you see where all the links are trying to go. When you make the system rigid then and integrate over the wheel, you realize that that is where the gyroscope's precession comes from.

[@cleon_teunissen]

About that idea of integrating over the circumference of the wheel, where did you learn that? The reason I'm so curious: on my own website there is an explanation of gyroscopic precession, and at the end of that explanation I corroborate the reasoning with an integration around the wheel. So I'm keen to find out whether someone else has had the same idea. Incidentally, I think the persistence of orientation of the string is not an instance of gyroscopic effect

[@erbro]

@@cleon_teunissen I was taught that at the university physics class in the 80s. If you make a ring, very narrow, and you can imagine it flexible and elastic to better understand the forces working on it, then you calculate the forces on the ring when you tilt the axis of rotation, you will see a function of the angle. In some points the ring will simply translate, but in some points you will see that the "links of the chain" have to change direction, requiring a transversal force. If you do this for all the points and integrate over the circumference of the ring you will find exactly the forces in the gyroscope.

[@matejlieskovsky9625]

Exactly! I like to explain gyroscopes by first teaching basic orbital mechanics. XD

[@cleon_teunissen]

@@matejlieskovsky9625 I disagree. For the gyroscopic precession to occur the spinning wheel must be rigid. With a flexing disk energy will dissipate. It is true that the plane of orbit of Earth satellites is subject to shift. As we know, this is put to use in the case of sun-synchronous orbit; the shift of the plane of orbit is such that it has a cycle of a year. That way the desired orientation wrt the Sun is maintained without having to expend propellant on that. If you would have a constellation of satellites, distributed roughly in the same plane, and at the same orbital altitude, then while their planes of orbit would all shift at roughly the same rate, the respective planes of orbit will not be _shared_ plane. This shows that the case of plane of orbit is not comparable to the case of gyroscopic precession of a rigid wheel.

[@matejlieskovsky9625]

@@cleon_teunissen ah, but if a satelite does an inclination change burn, then the plane of the orbit rotates around the point of the burn.

[@DeclanMBrennan]

This was really cool. Thank you. I wonder if a heavy rotating belt could support a fairly light gadget on rollers at the top? Maybe you'd need two belts rotating in opposite directions to keep the gadget at the top and twisting might also be an issue.

[@iseriver3982]

Steve 'put it on a drill' Mould.

[@andrewseburn]

Nono, that's an electric screwdriver..... Never heard it called that before.

[@fellipec]

So we found the inventor of the drilldo? (don't google it!)

[@michaelallen8374]

Steve, interesting video as always, thanks! Re the wave not propagating along the top half when moving from side to side, I think you already explained it. When you demonstrated plucking the top half of the string (7:36) the wave seemed to move away from the handle which as you explain is actually the wave which is moving towards the handle only the string is moving faster than the wave so it appears to travel slowly ( the wrong way ) along the string away from the handle. Hopefully that is correct. When moving from side to side the wave which is moving away is whisked away very quickly by the string making it invisible due to its speed, the wave which is moving the other way should emerge upstream of the rollers only again it is not moving fast enough so it travels downstream as before, but immediately meets the rollers all the time so any vibration in the upstream direction is immediately dampened to zero by the rollers themselves. maybe....

[@ikkonoishi]

When you move side to side you are adding a vector to velocity of the string so the effect propagates at the speed the string is moving. When you rotate you are changing the vector of acceleration of the string which propagates as the new acceleration vector overcomes the inertia of the previous one.

[@superhands290]

The top string is being fed through between two wheels, those wheels straighten the string and fire it out at high acceleration, which makes the wave extremely long and hard to see, but it is there.

[@dfgaJK]

7:29 When the string falls off it looks like a lagged out desynced object in a game!

[@jonnyreverb]

You are such a gentleman. I honestly watch your videos and try to incorporate your frank/open approach into my classroom.

[@Iceman259]

A string with a checkered pattern might be interesting for visualizing the waves’ speed relative to the string’s.

[@steventhehistorian]

Very cool of you to give Bruce Yeany the credit he deserves! He has inspired so many, as do you, Steve!

[@emfournet]

I feel like a stationary one that would plug into the wall and quietly keep a randomly-rotating string in a corner of you living room like a sculpture would be really cool...

[@zechsblack5891]

One like this with the rotational axis to make the spiral he shows at the end would be neat

[@thomasbarlow4223]

Yes maybe if it was inside of like a glass soundproof box cuz this thing is definitely not cuz I don't

[@JohnDlugosz]

On a stand, yes, but with some motion like a spinning platter on another platter to make it an interesting shape.

[@oisiaa]

If you notice he never has sound of the device. I have a feeling that it's quite noisy.

[@1gorSouz4]

I think it could be great for an art installation...

[@mengse00]

I thought that maybe the waves dont travel along the top part of the string, because the waves starting point depends on the change in position of the two rolling pieces. When you move your hand in one direction the lower part of the string moves with you in that direction and since the string moves away from you, the position of that moved Part of the string keeps moving forward. On the other hand the string on top moves towards you and so the part that is right in front of the rolling pieces will be pulled in and its change in its physical position will come out of the lower part. When you move in one direction the part of the string that is the furthest away will „feel“ that motion after all the positions before notice it. As you move your hand, the gadget pushes the the new position and you see the wave you created with your hand. Great video as always!

[@tomfeng5645]

Have you tried moving the shooter quickly towards/away from you? I was thinking that maybe *lateral* motion is fast but linear motion might be different, which might account for the rotational motion effect (a combination of the two). Additionally, does the time taken to restore the string to the standard location under rotation increase linearly with additional motion? (or alternatively, does the deflection increase linearly with rotation rate) If it's instead superlinear, that would make sense with slower restroation under forward/reverse motion.

[@tomfeng5645]

Upon further looking at this video, I also noticed an effect of the top "projected" part of the shoorter loop getting shorter under lateral motion, which may or may not be related? Also, let's compare what the actual velocity at the end of the string is under each type of motion. I count about 8 steps taken in 10 s, which is an average velocity of under 1 m/s and a peak of I presume around 2-3 m/s. Taking a 2 m estimate of the projection of the string, that means a rotation period of about 6 s (3 s if you use a shorter 1 m estimate) gives a same velocity as the peak, and about 20 s (10 s with 1 m estimate) for the average velocity. Notably at 5:25 the quarter turn takes about 3 s to readjust and about 5 s for a half turn which matches this rate.

[@tomfeng5645]

In summary I think at the moment my preferred hypothesis is that it's *not* slower to react under rotation, the rotation just has a much higher velocity towards the end of the projection than the linear motion as done in the video. To test this, we can try moving sideways at a faster rate to see if it shows the delay, or moving circularly slower to see if it removes the lag.

[@maxthexpfarmer3957]

I think the end of the loop definitely moves slower when rotating than moving laterally. I think that the gyroscope hypothesis should not he discounted so suddenly as an obvious difference between lateral and rotational motion is that rotation changes the angular momentum of the string.

[@johnquest3102]

Much more study needed, vary key parameters.

[@VitaliyKurokhtin]

Hi, Steve. One thing to point out is that linear velocity of the string is of the same value both coming from the shooter and towards it. Because otherwise string would either stretch or contact. To me the difference in behavior seems to do with different tension of the string in those areas. The string coming from the shooter is under compression, the string coming towards it is under tension. Same offset in both strings provides waves with different amount of energy. The string under higher tension will move faster to is initial position, the one under lower tension - slower and as a result will fade faster.Waves coming from the shooter as well have higher wave length, are more spread out. This looks like a transverse wave. It's velocity equals to frequency times wave length. Given the same initial offset both areas receive and same absolute medium velocity (linear string velocity differs only in direction), in both areas waves of equal length would be produced. String under tension produces wave of higher frequency (like in a guitar string), thus wave produced in area before the shooter will actually move faster than wave after the shooter, if measured from fixed point on a string. But string in the area before the shooter is moving in the direction opposite to the wave's, slowing it down if measured relative to the shooter itself. A similar example would be to throw rock off the bridge into a flowering river. As point of impact is moving away from thrower, wave propagates "outwards" (the circle grows), and if you would measure speed of the wave at points closest and furthest from thrower the values would be different. The wave at the closest point is carried away by the medium, but propagates towards the thrower. The wave at the furthest point is carried away just the same, but also propagates in the same direction. The difference in behavior to stepping sideways and turning may be explained by difference in impulse's vector it produces. While moving sideways each piece of string as it moves through the shooter receives impulse of the same value and direction, the difference is only in point of origin. While if you turn, the point of origin is the same, values of the impulse is the same, but the direction is not. In a case of sideways offset the tension between two pieces of the string stays almost constant, thus as offset point travels away from the shooter pieces move towards each other only a little. Given that speed with which string departs the shooter is much higher than speed with which shooter is offset, this effect is barely observed. But if two pieces are provided with impulse of different direction, as they move away from the shooter they'll stretch the string between them more and more, pulling string towards mid point. The section between them will grow in length over time and will be observed much easier. At the same time, you can observe as those pieces of string move towards each other. A similar experiment would be to throw rocks from the moving train perpendicular to it's direction of motion. If train moves in straight line, trajectories of the topics will produce parallel lines if observed from the top. But if train is turning, those trajectories will produce lines converging in center point of the road turn. An interesting experiment would be to vary string shooter speed and observe how it affects waves' behavior. Perhaps you could build one.

[@mehrad_ai]

Loved the Doppler effects reference for explaining the wave. The beauty of it gets clear when you realise the string is in a loop and basically the handle is “approaching” and “distancing” at the same time towards and away from the wave and that’s why the wave length is different. What makes it interesting is that the amplitude also changes

[@JanBartnik]

It looks like the speed/tension work as a parameter in a low pass filter. Reminds me of guitar strings... or rubber bands - if you don't put too much tension the amplitude of vibration is high and the frequency is lower. I also think that the velocity makes that string "tenser" in one axis.

[@keanamrazek3745]

I think your gyroscope analogy actually really explains it well, where there is momentum stored in the string that resists being distributed. It’s response differs because it’s a competently flexible gyroscope. I’d be interested to see what happens if you put it on a mechanism that allows it to pivot freely👀I suspect you’ll see a very similar response to a rigid gyroscope

[@h82fail]

Interesting video: 1. I think the top part is loose in a sense because its being thrown, so 0 tension to propagate waves? Can think of it like hurling a already loose string through space, if you poked at it, no waves would propagate because its all moving together and under no tension. 2. I think the curved part at the far end, centrifugal force + high tension is quickly flattening the waves? 3. The way the end stays stationary is awesome - I think I know what that is. A gyro only takes you so far, you really need them on more then one axis if you want stability. For this I think the curved path the string is following is not a solid disk, or single gyro, but a more complicated gyro which helps keep it put and stable. Wondering if the more twists you put it in, the more stable it is in a non-linear way - as in the time it takes to straiten itself back out is non-linear? Like half a twist around takes a second to return, but a full twist around takes 4 seconds. Like a motocross bike for example is more stable, and the person has more control when the rider turns the front wheel in the air - you notice all tricks involve this. The two gyroscopes (wheels) work much better to stabilize when they are not both on the same axis. And you don't get those weird single gyro effects you were talking about.

[@better.better]

I think the second clip from the end is where you'll find your answer, because there you can see two different types of waves transitioning into each other. I think it's going to be more of the same as what you've already mentioned: the difference between one side being in tension and the other side not, vs coordinate change of the equal tension zone.

[@OneOfDisease]

I would be interested in seeing a scaled up version that can shoot ball chain to see if there is any differences with the extra mass and the more rigid structure.

[@MrLareneon]

The difference between the side-to-side steps and the turning really seems to be an agular momentum issue. Something that big moving in a circular path has a lot of angular momentum. Side to side is simply not as much momentum to overcome. Great vid!

[@Lprsti999]

Yeah, I'd be interested to see how the string reacts to faster lateral movement, like holding it out of the window of a moving car, perpendicular to travel. I'll bet that as the car's velocity approaches the angular velocity of the far end of the string when turning, you'd start seeing distortions similar to rotating the shooter. That said, I think there's also a large inertial factor to why the string responds to rotation so slowly.

[@dariusduesentrieb]

That's what I am thinking, too. Maybe this effect would already show when walking side to side a bit faster (or better running).

[@TlalocTemporal]

@@Lprsti999 -- A linearly moving reference frame and a stationary reference frame are indistinguishable. You'd want either the car's *acceleration* or the higher wind resistance, although the wind would be a different effect.

[@tmarritt]

Yup it still moves in the side to side but distance travelled at the far end is so little that its barely noticeable. Turn it in the radius of a circle and you have massive increased the difference between the distance moved and the far end and the projection point.

[@MrGreenReefer]

Your drill set up PROVES the 'wave on top" issue VERY clearly. As you move the device back and forth, the wave length on the bottom is very short and is clearly visible, but the wave is there on the top, obviously as you are moving your hand or body back and forth thru space. the issue is, the wave length is just much longer than the top half of the string arch so the end seems to follow you, but it is truly just following its very long (3m+ im guessing) wave.... Just as when you spin this device at a higher speed, it makes that top wave (or coil now) tighter and now visible, but clearly shorter, as always, than the 'tension' or bottom half wave (or coil). I love how you expand then blow my mind every video! great stuff, and umm.. i want a rope thrower too!!

[@spliter88]

As for why the string looks like it doesn't have waves when moving side to side, I think I may have an explanation: When you pluck a string on the top part the one coming to you is slowed enough that it start going away from you. However when you move side to side, the origin of that movement is at the string shooter's rollers. So that wave still exists it just goes down the string fighting against the speed (higher tension at the rollers give it the boost to not go up), meanwhile the part of the wave that goes with the string just goes around so fast you don't see it. I also think you might be wrong about the turning, it's not that you impart a wave on top and bottom at the same time, that still works just like translation. I think it is essentially the gyro effec of the string, and the reason you don't see any procession, is because you're holding onto the string shooter. I think what's happening is that you have the linear momentum of the string coming out of the shooter trying to fight the angular momentum of the entire string, and as you keep adding linear and angular momentum on one end, and rooting yourself to the world so you don't counter-spin eventually the angular/linear momentum from the string shooter wins. Still I wonder if when you turn if the string rolls along its movement axis, would make sense to me as that's yet another way of preserving the original angular momentum.

[@georgmagi4403]

Ok

[@deadfishyarou]

Yea I had the same idea, sideways movement doesnt cause a backwards wave because the boundary itself is what is acting on the string!

[@ericschumann4213]

I definitely saw the wave in the top string mentioned around 11:40. The key is that the wavelength is far longer than the string, so all you can see is a small part of the waveform at any given instant. If you pause the video during the side to side perturbation, you can clearly see the curvature of the string that is indicative of a wave. If you could capture the discrete coordinates of the string along the top of the curvature, you could do a discrete Fourier transform on it and that would give you the frequency of the Doppler shifted hand movement. After accounting for the Doppler shift, the frequency of your hand movement would be the primary frequency remaining.

[@Justsevenwords]

Dang. I had a handheld one of these at least 15 years ago my dad found at an airport. Thing was cool

[@klaudspeed]

I really thought this was a common toy till I went through comments... I remember easily breaking the motor when the string would get knotted.

[@PentodeSensations]

This reminds me of electricity, quiescent draw, instrument amplification, and signal-driven changes in impedance against a coil. The speed of the string is a "voltage", the energy of the moving mass is kind of like a big battery/capacitor/filtering network, and there's a "quiescent draw" against that constant charging of the system like a bias against a tube passing current, which I think is a result of exterior forces imposed onto the system (friction and gravity). Your impressions onto the string and the movements/axis accelerations of the shooter/spinner would be changes in the control grid voltage of either a triode or pentode, and the behaviour of the string demonstrates changes in impedance. The simpler demonstration is in just touching the top or bottom of the string as it moves along. This is most like a triode, in my opinion. I like to see this like resolving the signal path and draw characteristics on a circuit. When tapping from the edge of spinner's top, you can see the effect/signal amplify at the "peak impedance point" for a moment. If you keep your finger in place, you've create a new bias/impedance point; and if you waggle it, we can see an amplified waveform. Plus, we can see the draw can be seen/felt at the returning edge at the bottom of the spinner. When tapping it from the bottom, I think this is what might me a "cathode follower" in tube circuits. I think the bottom taps and friction slows the string down, and drags the whole system down (increasing the system's impedance), like adding a resistor to restrict cathode flow, affecting the global bias point. Not to get super nerdy about it, but this "cathode follower" design is a common low-impedance drive circuit in tube amps, and is known for smoother overdrive characteristics. Tapping from the top is maybe like a later Fender design (AA864 circuits) which sound a little harsher and blockier, exaggerated even when overdriven. When you tap the outside edge (where impedance is greatest), it's more like a microphone, or, your finger effectively turns into a resistor/capacitor, eating some voltage/speed, feeling current/heat on your finger, and ability to sense other waves travelling through the system in the form of reductions and increases in voltage/speed and friction/current/heat. The less obvious/probably incorrect effect I'm seeing here is in the side-to-side motion. I feel this looks like pentode behaviour, where the voltage is held more constant (we're not messing with the spinner's Y-axis), and we're applying a considerable X-axis. Watching it be resolved, I want to say there's a smaller drop in speed/voltage/Y-axis energy for a considerably larger distance travelled across the X-axis, and the system resolves the energy on the X-axis as if it were "capacitively" more efficient as a result of your arm become a part of the impedance network. Which is a mixed blessing. Smaller forces might not require any extra input from your arm to control the system gently. Just as well, too strong a swing would overwhelm beyond reasonable correction, and your string turns into a whip (this is when vacuum tubes arc). Also, when you're rotating the string-spitter with a drill on your back, I think this is maybe a "visual" of a parasitic oscillation. With guitar amplifiers especially, it's sometimes possible to produce a high-pitch parasitic ring with too much high frequency bypass. It's also possible to produce oscillating hums with over-filtered or poorly arranged power filtering schemes (usually an inaudible low 4-Hz up and down drift that shows up on the speaker output).

[@wymondgoolsby8070]

when I was 10 years old my mother took me to Disney land. The first day she picked one of these string rollers. I played with that thing non-stop for the entire trip. Rolling it all over walls, ceilings, anything I could find. I lost it on that trip and I haved never found a toy more simple and fascinating to play with as a child.

[@JohnDlugosz]

You "lost" it on the trip? Tell your mother to give it back and you'll only play with it at your own house.

[@kpatriots8]

Something about him lying on the ground and watching the wave spin makes me so happy about the love he has for the beauty of the laws of physics.

[@DennisXiloj]

Me looking at the title: oh no, mould effect 2.0?

[@seankuhn155]

The top part of the string DOES make a wave when moved side to side. It's period is just much longer. You can get three or four periods on the bottom portion of the string, but less than 1 on top

[@pedrowaki7376]

It’s so satisfying to watch Steve getting amazed by a toy, feels like we’re never old enough to stop questioning why stuff happens. Great video!

[@NandR]

Instantly pre-ordered one. I have ideas for this already. I need a strobe light too. And some glow in the dark string would be cool.

[@samudrajs5409]

You should make another video on this topic. About the waves. Explaining wave's group velocity and phase velocity in detail. You can also include slowing down of light in this way. Waiting for that.

[@jamielapsley4933]

That bit at the end with your kid explaining how his new gadget works was so wholesome :') thanks for sharing your random but intriguing knowledge once again!

[@byronwatkins2565]

Wave speed on a string is sqrt(T/mu) and the chain's tension varies with height; so exactly what point in the chain is the chain speed equal to the wave speed? In fact, the tension in a vertically dropped chain (suspended from one end and dropped) is zero if you neglect earth's tidal force. Immediately after the rollers the tension approaches zero -- possibly is negative for some circumstances -- in which case wave speed is zero (or possibly imaginary and dissipative); thus no wave propagates. Applying friction to the top of the loop increases tension after the touch and greatly increases wave speed... the wave is then reflected by the rollers and the reflection is inverted. The string motion is the sum of these two waves.

[@CAVEMANMUSIC-gg6uf]

The top of the string is in tension and the bottom of the string is in completion thus the wave is a lot more promenent in the bottom than the top

[@Vlow52]

The string shooter should be tested in a vacuum conditions to see how much of air pressure with molecules coming from the roller are affecting the path.

[@kenshiromilesvt.7037]

I doubt it would be much beacause of the small surface area, but would definitely be cause for testing!!!

[@Vlow52]

@@kenshiromilesvt.7037 open space would be perfect hah, but talking about more grounded setups, I think two long plexiglass panels could be placed in parallel, so having a small gap enough to have a space for a linear string path

[@kenshiromilesvt.7037]

@@Vlow52 that’s a great idea

[@adaetz1042]

@@Vlow52 Could be very interesting, although large flat surfaces are extremely susceptible to failing under the immense pressure gradient caused by pulling a total vacuum at sea level. That's why most vacuum chambers you'll find are circular, since the radial symmetry resists deformation. Very thick plexiglass might do it :)

[@Vlow52]

@@adaetz1042 you’re right, it got to be thick ones. Yet, another idea without vacuum chamber is to blow a white smoke near with the shooting mechanism, similar to the automotive aerodynamics test, but it may be tricky to get a stable flow. Or maybe film the sound waves using a concave mirror, like Dustin from SmarterEveryDay did with the bullet tracks :)

[@andreidei]

side to side movement applies a lateral force on the loop, while the spinning movement applies a force towards the spinner - the force with which the string is pushed / pulled can be considered bigger towards the spinner, and gradually fades towards the end of the loop (the tension is not really constant => we can consider discrete forces across the length of the string), but the force from the spin is constant => the loop lagging because is basically pushed more towards you as you travel away from the spinner (by the resulting force from spin and push / pull)

[@justrecentlyi5444]

I'm thinking that this analysis would benefit a lot from slow-motion footage! Also, I love the mesmerizing images from the double spinning demos.

[@toohardtowatch]

I'd like to see this operate with a section of the string dyed black, as well. It's hard to get a sense of how quickly the string is moving.

[@xaracen7207]

if you look from the top as you rotate the string shooter you see that arc that you would see in the chain fountain, changing the direction effectively makes a chain fountain, so whatever forces govern the string fountain also causes the string to twist in the way it does.

[@davidonfim2381]

I think it would be incredibly useful to dye a bit of the string so that we could easily see the direction that the string is moving. It's not easy to tell, and I keep getting confused about what direction it's spinning.

[@fweaks]

I feel like it's moving waay too fast to see such a mark.

[@dripppztv7246]

Bro I've been following him since like 50 followers, this was by far the invention I've been most excited about and now your doing a video about it, thats crazy.

[@Arzack711]

Looks like I've been enchanted by Steve's big, blue, anime eyes. Mehdi's words had been deeply planted into my mind and I can't get rid of it.

[@amontaval]

I ordered a Zipstring in the US on November 21, 2021 and it FINALLY arrived today! It is lots of fun.

[@jaredf6205]

I ordered one yesterday and it shipped today lol.

[@schwuzi]

Same here ordered Nov.21, arrived yesterday

[@FaultyMuse]

I think we actually *do* see the wave propagating from the top of the string when you move the shooter laterally. The problem is that the wave originates from the shooter itself so unlike when you pluck the top part of the string, the wave is only propagating AWAY from the shooter and moves far too fast to see. In fact, I think what you're interpreting as the string following the shooter when moved laterally, is actually just the propagation of the wave away from the shooter till it hits the vertical "boundary region". Would be interesting to see slow-mo of the shooter being moved laterally to see if we can verify/disprove this hypothesis.

[@brendanmcculloch2406]

Exactly my thoughts

[@TheZanzaroni]

I think that the reason you don't see waves at the top is tension again. The speed of sound as you said in a string is dependent on the tension present on it (it's tension divided by density all in a square root). Given that tension above is positive and is possibly much larger than the density of a conventional string, the information for side by side motion is transmitted much quicker than below where the above model does not hold true since tension is "negative".

[@connorsherwood636]

The real string theory

[@SteeveEfnet]

I think that the top string is being compressed along the length as it is being pushed outward at high speed, making it act more like a solid stream , as the tension release going towards the bottom part you end up with slightly looser string closer to the end of the loop which allows it to have more flexibility and allow to bend a lot more.

[@patman8137]

I have questions. Have you tried to rotate the strinthing, so that up goes down ? Could you manage to build this into a device, with a very, very long string? What would happen to the wave?

[@Clarionut]

Fascinating! The trajectory of the rotating string shooter looks similar to that of some strange attractors - particularly the Sprott attractor which has a central rather tight spiral and returns via wider loops around the outside. Coincidence???

[@sebbes333]

8:10 And "they" said: *"yOu cAn'T pUsH a StRiNg!"* and here is proof of how wrong they were! :D

[@catastrophe8336]

I absolutely live how you take the time to see if anyone else has done a video on a subject and even go the distance to tell us some of the differences between your videos and the others. The way you present the information is really cool makes it amazingly entertaining, have you ever thought about being a teacher?

[@Paul-sj5db]

My first reaction when I saw this was "oh no, it's another Mould effect".

[@davidanderson8628]

What happens with different stiffness or elasticity of the loop? For example, would a thin wire (stiff, no stretch) behave different from a rubber band (stiff-ish, lots of elasticity). Or a ribbon (lots of stiffness left-right but easily bends around the circle). Or dental floss (extremely light-weight). Or a loop of the chain stuff you used in the chain fountain videos! So many possibilities to mess with the behavior!

[@SpectrumDIY]

Lol, "and here we have a wild mould in his natural habitat, playing with his effects"

[@JohnDlugosz]

Your question towards the end, I think you already explained earlier in the video. You can't get a visible transverse wave on the top part when you move the handle laterally, because the wave _initiates_ at the wheel. Waves in the top part only propagate towards the wheel. (or more precisely, you won't have a significant fraction of a cycle of even a single wave present, so it looks like a straight line)

[@stephenbarnard2856]

When you attached it to thd drill, the helix shape was pretty interesting. The frequency in the z direction of the outside string is far less than the frequency of the inner string.

[@aaronbredon2948]

You and mehdi both started with an understanding of some but not all the causes of the chain fountain. There was a tiny but significant downwards pressure from the chain on the container which helped the chain rise, and there was also another force effectively trying to keep the loop stable. When the weight of the chain or the flexibility of the chain changes, the relative magnitude of these forces change, and this alters how the forces essentially balance. I think part of the reason the rotation last longer is one of the causes of the chain fountain - you are changing the direction of the string, so it wants to hold the shape of that curve, and changes only slowly. On the other hand, when you shift side to side, there is less of a direction change, so it resolves much faster. I did see a minor wave effect once when you were shifting the shooter back and forth rapidly. You have to shift the string left 1 foot to get a 1 foot shift in the furthest point of the string, but a relatively small turn will move the furthest point even more than that. And given the speed the string is moving, you need to shift quite fast to have an appreciable impact, whereas twisting even 10 degrees has a large impact on the furthest part of the string.

[@joewwilliams]

Just gonna keep milkin that chain fountain, eh Mr. Mould Effect?

[@hart-of-gold]

2:43 You can see the wave in the top string, because of the angle of the spring to the camera compressing the appearent wavelength, it stands out.

[@theSwoderman]

I love the faces Steve makes when he's testing stuff like "wtf is going on here"

[@Regularsshorts]

The tension on the top part is higher than in the bottom because it is pulling top part and pushing bottom away. So that is what not makes a wave on the bottom and not on top.

[@Grahamaan27]

Steve , you asked why the string doesn't have a wave on the top, but I think you did provide an explanation for this: the wave is propogating out from the handle both top and bottom. On the bottom the wave speed is faster than the string speed, so it propogates slowly. At the top, the wave speed is combined with the string speed, so the string motion elongates the waves -- so long that you cannot visibly perceive them. However, you actually can see the super long wave if you step back and think about the horizontal movement as the entire wave.

[@BooBaddyBig]

I think you made an incorrect assumption that the tension in the top of the string is lower. The device is NOT the only source of tension here! The tension along the length of the string travels at high speed (maybe a hundred miles an hour or something), the weight (and momentum) of the string itself creates tension. The bottom is actually at LOWER tension. And that's why you can see the waves. The waves at the top go too FAST, and are likely being damped out by the air and the string itself, as well as being carried along with the motion, at the bottom they are somewhat under-damped, and move much more slowly. The rotation effect is basically gyroscopic-but there's no strong bearing. If you look at the string entering the device, it lags, and it leaves leading. That's the device creating the precession. Note that the loop is angled to the vertical, that's the wobbly string version of precession.

[@pianosidechat]

the part of the loop being pulled into the rollers definitely has higher tension

[@BooBaddyBig]

@@pianosidechat Not necessarily. It depends on the air drag, the g-force, the weight of the string etc.

[@pianosidechat]

@@BooBaddyBig those forces would be negligible. The weight of the string is equal on all parts of the string. The centrifugal force clearly is much greater than gravity. The loop would perform similarly in 0G and in a vacuum.

[@BooBaddyBig]

@@pianosidechat Potential energy is a whole thing. It's obviously not insignificant relative to the centrifugal potential otherwise the string trajectory would be essentially circular.

[@martinmehus1406]

Okay I have an idea why we don’t see a wave at the top. When you move the handle quickly sideways back and forth, it is quite the same as plucking the string with your finger, only that the finger is replaced by the rollers. There is however one major difference: When you pluck it with the finger, you removed the finger afterwards, while the rollers never leave the string when they «pluck» it. So when you move the shooter quicly back and forth, there is a wave created in the two directions. One is going along the direction of the string, so we don’t see it since the wave length is so long. The wave in the other direction is created at the other side of the rollers, and blocked if it tries to go through the rollers to get to top. I guess the higher tension in the lower string also plays a role here. Since the tension in the lower string is higher, the wave speed is higher, resulting in the wave created in the rollers will move away from the rollers on the bottom side, just as you explained. The wave is therefore never able to reach the top side. So the wave we’re missing at the top string is actually the wave that we see in the bottom string. I think this is the effect at play here, however if the tension in the bottom was lower or the string speed was higher (so that the string speed is higher than the wave speed), there would still not be a wave at the top, since it would be stopped by the rollers. In this case, there would be no wave on the bottom nor the top, since the bottom wave moves faster than the string and is stopped in the rollers, and the top wave has such a long wavelength that we don’t see it. I’m not sure if it’s possible to get the wave speed higher than the string speed tho, since increasing string speed will increase tension, resulting in higher wave speed. The thickness and material of the string could also play a role here. That would be interesting to see.

[@outside8312]

I had one of those toys as a kid. It had flashing lights and played music too! I loved it until my friend "borrowed" it and I never saw it again sadge 😔

[@michaelr721]

The reason for no seeming propogation on the top string with the side to side motions is the fact that a wave it does propogate but the rapid movement of the string shooting away makes any action applied to it relatively subtle and weak. You would need to shake it from side to side more forcefully which would perhaps be difficult if it tangles or dislodges in that event. But the reason tapping it with your finger works is that if you think of the string zooming past your finger as your touching it, you're essentially putting a force on a greater surface area and creating a larger impact to generate a wave.

[@BerliozT]

Im just curious if a cat can play with it. Can you imagine the hours of bonding you would have with your cat over string? Top comment has a point lol

[@the2purplecats]

Yes

[@9000leo]

My go at the difference between changing direction and moving side to side is the difference between bending moment and shear force. The shear force (side to side) is responded in an imperceivable time, evident by the fact we never see the strings going side ways at an angle. The bending moment is responded very slowly on the other hand. The difference here is when a rigid body is bent, though the extra stress (delta to the nominal axial tension) goes from compression to tension as you go out on the bending radius. Whilst a rigid body has a large bending radius, a string does not. The bending can be localised within a very short distance. The net force is neutral to the nominal tension, leading to the only apprent movement is a slow propagation of the string turning into the new direction. The shear force on the other hand has a net force that can only be resolved by an accerlation in movement thus a close to immediate response. The difference in response to the change in direction between the top and bottom could be looked into further.

[@jordanmasse6811]

My mind broke for a second when the string fell 7:25

[@ValpoPhysics]

Brilliant job with the drill. A marvelous new observation. To see the wave propagating around the loop, you need to change the string speed. I'll make a video for you.

[@ValpoPhysics]

You missed something. kzbin.info/www/bejne/pJiZqn2PYtiHkJI

[@benweieneth1103]

Regarding the lack of waves on the top string from side-side motion: As you said previously, the top wave is actually propagating _toward_ the handle and being carried away slightly more quickly by the motion of the string. When you move the handle, the reverse wave that might have been visible on the top string ends up on the bottom string instead.

[@Berkm00n]

I think the waves going in the direction of the top string have a bigger wavelength and when this wavelength is bigger than the length of the top string, we dont percieve them.

[@latenightcereal2390]

I love that you're talking about it as if you're personally interested, and then in the video you're completely tuned out, just looking at your phone. It's like your a hot back stage that has to shake a tree or something, and you're just sitting there shaking randomly, with no real concern or discernment

[@RevDrMatt]

You should make a giant one with a pitching machine and a firehose.

[@eugenejosephfoss]

I think there is more tension in the top of the loop, usually. You can see this because the bottom of the loop sags more than the top does, which is easier to see when you transition to shooting straight upwards like Bruce Yeany does in his video. This larger tension increases the wave speed as you observed. When you pluck the top of the string, you pull the end of the loop towards you slightly, causing the top to have less tension for just long enough for a wave to propagate.

[@peromonet8036]

String TENSION is much higher at top where the string is pulled in, therefore no wawes there. (Any wawe is pulled in) Elementary my dear Watson 😊

[@kindbud]

I had a few of these as a kid, we modified 2 of them to combine em and spin a double size string and also play with it as a jump rope

[@spencerparker4910]

He actually did it! I took a university course with one of the inventors. I sat near the front off the room and heard him discuss some ideas he had for the string shooter with our professor after class. I am very impressed with what he has managed to accomplish

[@JamMastaJew]

8:50 what you've said earlier: when you flick the top part of string and see a wave going slowly away from you, that's actually the wave moving along the string towards you but the wave is slower than the string speed. When you move the string shooter itself side to side, there is no string between the origin of the wave and the string shooter for a wave to travel down; the shooter is the origin. The only wave being created on the top string is the imperceivable one moving quickly along the string away from you.

[@guessnot8015]

Can you try to use it upside down and see if it works, if it works find if it's the lower or higher string produce wave if you move sideways.

[@tonygluk1]

Regarding the question at 8:55. I think since the visible part of the top wave originates before the point where the string goes through rollers, all effects that we would otherwise be able to see are just flattened by the rollers.