Are solid objects really “solid”?

[@AlphaPhoenixChannel]

Frequent question replies and corrections! Sup everybody! I'll edit this comment when common questions show up or people find errors I want to correct! (I know there will be many, but I don't know what they are yet, or I would have put them in the video!) #0: the "model" I use to describe interatomic bonds is ludicrously oversimplified, but it's kinda close enough to make it look like a spring. #1: at 20:02 said "poisson ratio" when the graphic clearly said "E" for Young's modulus. It's almost like filming brian can't even see the things editing Brian pastes on the screen... #2: lots of people asked about the delay in the wires or sensor squish. if there was a noticeable delay, the plot I show at 17:26 would have had a nonzero intercept (if the spark between the hammer and bar sparked early, the intercept would be negative, and if the sensor or circuitry added a serious delay, the intercept would be positive. If both are happening and cancel out, they happen every time the same way, apparently! #3 yes everything from water, to steel, to neutronium is somewhat compressible (the nutronium comments were great - thanks! Apparently in such a structure held up by Pauli pressure, Vs approaches the speed of light. Now I’m wondering what the refractive index of nutronium is and if it’s crystalline or not…) #4 I've had enough people ask about hitting the bar witha hammer moving faster than the speed of sound that I actually looked into it. I'd need an ultralight projectile like railguned into the end of the bar in a big vacuum chamber - there's no reasonable way I can think of to make something go that fast but I if can think of one I'll make a video. bottom line though, as long as that impactor isn't actually penetrating the bar of steel, the wave will still pass through the steel at the speed of sound.

[@theoreotically]

20:02 to 20:10 You say "poisson ratio" instead of "Young's modulus"

[@MegaBCAD]

Dustin at smarter every day has a canon maybe a team up

[@JoJoV111]

Sounds like we need to get you more patreon supporters so you can buy a railgun and giant vacuum chamber 😂

[@aeyde]

amazing video!

[@hulkgqnissanpatrol6121]

7:14 wouldn't you actually be reading the devices inaccuracies? Most if not all have a 1-2 + - %. I've Never seen one 100%.....

[@michaelmolter8828]

That feeling when you apply a small theoretical correction and the model snaps precisely to the empirical data is probably the single best feeling in the entire world. You don’t get it often.

[@AlphaPhoenixChannel]

I feel like that’s what I live for

[@JohnSmith-hp9ds]

I usually have the opposite happen where I'm like "If I just change that only little thing it will be perfect" and then everything is on fire, I've created trig functions out of thin air turnips, and ford 150's, and 1=the cube root of salsa

[@adrycough]

@@JohnSmith-hp9ds if 1=the cube root of salsa, wouldn't salsa just equal 1?

[@rickascii]

@@adrycough -1/2 +/- sqrt(3)/2 i

[@zyeborm]

@@JohnSmith-hp9ds you should have used a spherical cow of uniform density.

[@nashsok]

"The more correct a physics model is the more painful it is to use" That's why experimental physics is so great - The universe takes care of all that figuring work for you!

[@AlphaPhoenixChannel]

In my mind experimental physics is essentially trying to find an informed equation that captures as much of a real effect as possible without just making a lookup table. Like you should be able to fit a curve but also extrapolate and use your equation to predict unseen situations.

[@willthecat3861]

@@AlphaPhoenixChannel Can you give us links (or a bibliography) to/of your published papers in materials science,,, so we can read about your research.

[@mikip3242]

@@AlphaPhoenixChannel I liked that phrase a lot. Some theoretical physicist are always saying that physics is elegant an beautiful and they derive that "elegance" property from the simplicity of the models and equations in relation to the complexity and variety of observations they predict, but in fact those, let's call them platonists, are continuously neglecting the fact that indeed the more correct models depart from elegance quite a lot and tend to explode in complexity whenever you really want to test detailed phenomena.

[@AlphaPhoenixChannel]

@@mikip3242 I’m not sure I buy that. There are some insanely precise theories that are still extremely simple and elegant. A lot of physics is based on geometry and geometry is pretty perfect Edit: Look at the inverse square law - crazy simple to calculate, exists because everything that spreads out evenly in all directions scales with the surface area of a sphere. It’s more of a property of our universe, but very boil-down-able to just C/r^2

[@goclbert]

I had a professor say "we let the universe do the computation for us"

[@PracticalEngineeringChannel]

This has application in structural pile testing, because a hammer impulse happens too quickly to load the entire member at once. Static tests are expensive because you usually have to build two reaction piles just to apply the force. There's a cool method called statnamic testing that uses explosives to create a slower impulse on the pile as a load test.

[@baijokull]

Which we all knew already because we watched some guy's youtube video about that just the other day :D If only I could remember who it was, probably Physics Girl or Minutephysics...

[@LampsAreCool]

"Slower"

[@AlphaPhoenixChannel]

I way sitting at lunch one day watching your pile driving video and when you got to the bit about the loading depending on the speed of sound in the pile, I was internally doing that Leo pointing meme going “oooh ooh I recognize that!” cause I was working on this video at the time and was very excited to see it matter somewhere!

[@Matt-dk3wl]

Always nice seeing your heroes are watching the same stuff as you.

[@AlphaPhoenixChannel]

I couldn’t run around the company cafeteria holding up a picture of an explosive pile test on my phone yelling “do you know how cool this is?!” Because theyd think I was actually insane, but ya know, I wanted to 😁

[@ChaosUnit178]

I never really considered how soft, flexible, and noodly steel is until I became a machinist. Now it's a constant thought and struggle in my daily life.

[@TsunauticusIV]

There is a KZbinr called Robrenz. He doesn’t make many videos these days but he has some amazing videos. He shows how much machined items can change size with just the heat from your hand. He measures into the millionths for machining. Absolutely blew my mind. Machining itself is an interesting field. Toss in precision metrology and you’ve got AWESOMENESS. lol.

[@MyKharli]

I have seen improperly fixed (ie no slip sleeve) large steel flues rip out ceilings , upstairs floors and roofs on first stove light up due to steel expansion ! (and people taking on jobs they shouldn`t)

[@quint3ssent1a]

Yeah, I've thought steel is hard and tough until I once bent a 1cm. thick steel rebar just by pulling at one end (it was a big leverage, but still.)

[@Staroy]

@@quint3ssent1a Try that with a tempered 1cm steel bar

[@arthurmoore9488]

@@Staroy With a long enough bar it would still move. Depending on the temper it would probably then crack, but the point still stands. A 100m length of 1cm tempered steel bar can almost certainly be moved by hand.

[@essigautomat]

The end explaining the methods and failures was even more interesting than the initial question, great video 👍

[@daanterra2583]

Yes I thought so too :)

[@hughobyrne2588]

Particularly the graph with the zero intercept. I wasn't fully sold on the experimental technique until I saw that.

[@AlphaPhoenixChannel]

While editing I wasn’t sure how much of that I wanted to include but I’m glad I did and I’m glad you liked it! The setup is always a struggle but this one has some very nicely tangible and easy to talk about problems

[@drangus3468]

@@AlphaPhoenixChannel That was the most interesting part for me too.

[@miri.mayhem]

exactly. from the main part there's only one specific thing to learn. From the setup at the end, there was so much more related to learn about the properties atc

[@EngRMP]

As a 66 yo electrical engineer, I've found myself going back to learn physics over the past 20 years. Your demonstrations of physics are REALLY well done... really informative. Nice job.

[@zhou_sei]

yes, everything is so intuitive. the answer (after watching) seems so obvious. before, i had zero clue what the answer was. hiding in plain sight. indeed, VERY well done demonstration. thorough, and yet captivating.

[@kingpiggins292]

I more of a medium rare person myself

[@olivierdulac]

@EngRMP: I would love to know any good sites or youtuber that you would know that are both very clear about how electricity (and later, electronics) works, but also not too slow to explain things (time is precious). If you know some good ones, please tell us.

[@EngRMP]

I'm sorry Olivier, I wish I could help you... it's a complicated topic. However, this gentleman recently made the best video I've seen that explains voltage, which is really one of the most difficult terms to understand. Once you understand voltage vs current, you'll be ready to understand resistance vs capacitance vs inductance. If you have a good math background and are comfortable with the concepts of integration and differentiation you'll enjoy learning about circuits with these various components. Going on from there you'll learn that diodes have beautiful exponential properties, and that leads to transistors. I'm the wrong person to recommend sources of info because I'm coming at it from a difficult angle or need.

[@BeachesNguns-fl4cx]

😂

[@account0199]

I find the fact that you ALSO explained the "failures" in the experiment, as valuable as the results themselves.

[@qwertzuiopqwertzuiop2107]

yep, if it was just the result, I wouldn't have learned something new. But the 2nd part of the video was really interesting to me. Kinda blew my mind

[@inyobill]

See "Science".

[@pirojfmifhghek566]

"We fucked up." "Booo!" "But we wrote it down!" "Yeah, science!"

[@Ragnarok540]

Is rare to see that in a KZbin video.

[@inyobill]

@@Ragnarok540 Also "rare"? ;-D You should see some of my typos, that's strictly amateur level mistake-making there,

[@Mathijsvanwijk]

This is so much more interesting then the majority of shorts and quick videos you can find online. I wish more people took the time explaining and testing nature. Not for the views but to actually learn stuff. Great channel!

[@davidn4956]

I'm glad somebody else has had this exact question before. Always thought about how faster than light communication could come down to just having a really long stick, knew that it couldn't be right, and now I know exactly why it couldn't.

[@JoshWiniberg]

I had EXACTLY the same idea when I first looked up this topic. Although, you wouldn't actually need a long stick, it could be measured through the movement of any object.

[@boggless2771]

I know how to move something faster than light. Get a very strong laser and point it at the left side of the moon. Then rotate the laser quickly to the right side of the moon. If you do it fast enough, you will move a point of light faster than the speed of light.

[@NeinKyori]

@@boggless2771This has been explained as impossible by a lot of people before In short, if you have a constant light souce (laser pointer in this case) the light coming out of it is a constant stream like water from a pipe And what happen when you move the pipe left to right quickly? The indiviual water droplets separated from the continuous straight stream. However, that doesn't mean they will travel any faster toward the wall in front. They only give the illusion that the water splash on the wall from left to right travel faster than the speed of water coming out from the pipe, but if you exam closer you'd see a delay, an arc of water due to the speed limit

[@isaiahmumaw]

@@boggless2771Sure, but that point doesn’t represent a physical object. The photons on the left side are not the same as the photons on the right side. Nothing is transmitted between the points.

[@boggless2771]

@@isaiahmumaw right. I said something ;) No information is moving ftl. But "something" is moving at that speed.

[@thomasneff376]

Yes! Fellow engineer here. Thanks so much for explaining how you learned the real final result and why it affected your test. I learned something new today! It's such a good feeling as an engineer to see the theory match exactly with physical objects. It's like learning how to predict the future or something.

[@m3chanist]

That's one of the defining qualities of a theory as opposed to a hypothesis or law for instance. A theory is predictive, it can accurately predict the result of an expirement that tests it because it is universally applicable to its subject.

[@kenrolt8072]

There are at least three solid wave speeds involved: (A) rod or bar, (B) plate, (C) infinitely-sized solid. Each of these involves the vibrations of the molecules (which is the same for all three cases) but the effects of the boundaries (the visible surface of the steel) allows the molecules to move transversely rather than along the length of the bar. This has to do with the spectrum, or frequency content, of the source --- which is a hammer impulse. At low frequencies (related to how long the duration of the hammer face acts on the rod), the bar or rod appears to be thin relative the sound wavelength, so you observe the rod speed. The bar gets progressively fatter and thinner as the wave moves. For steel this is around 5100 m/s. If you did the experiment with a thin plate, you would measure around 5400 m/s, because it can only feel the boundaries through the thickness direction rather than all the way around the plate. In an infinite solid, where the waves never feel the boundaries, you would measure around 5900 m/s. The wave has no where to go. A lot of this behavior is related to the Poisson effect for static loads on solids, and the math to show the 3 waves speeds involves the Poisson ratio. The speeds are approximate depending on the chemical composition of the steel. I don't know if anyone who commented already posted this explanation so I apologize if they already did. There are also shear and interface waves that are beyond what I wrote here, hence I said that there are at least three mechanical wave types. Great work BTW.

[@caghantuncer6081]

Thank you for the great explanation

[@audiomystic]

Wow, what is your background? That was a fantastic explanation. So true about the spectrum of the strike.

[@brendan12882]

Rule #1: Everything's a spring

[@a-a-ron8201]

Rule #2: Everything’s a hammer

[@SkKedDy]

Rule #3: Everything's a rule

[@Itstoolateohhwell]

Ahh spring theory

[@1fattyfatman]

@@Itstoolateohhwell bro…

[@philiphunt-bull5817]

​@@Itstoolateohhwell thank you

[@FPSG]

I love this video. As a machinist, we have a saying, " Everything is rubber." It's an anecdote about the difficulty of measuring things to extreme precision. There are literally calculations for the deformation of ruby on tungsten carbide . Sure you don't need it until you are measuring tens of millionths of an inch and by that time you need a climate controlled room and can't touch what your measuring for days before taking the measurement because the thermal expansion will throw it off more then the compression. They still exist

[@ainzooalgown6450]

That was so cool. As a laymen, I have no idea what you're talking about but it's cool 😂

[@thienthetyga3462]

@@ainzooalgown6450 he means things are hard/tedious to measure with extreme precision when you want extremely accurate results because things ( beside water) tend to condense and take up less volume when it’s cooled, where the volume (of tungsten) would expand ever so slightly if it was heated.

[@Ailtir]

Water is most dense at around 4°C at standard pressure if I remember correctly so it will contract as it cools from 4°C down to 0°C where it again expands as it turns into a solid.

[@HaasGrotesk]

"tens of millionths of an inch" The fact that you still use the imperial measure system as a machinist is amusing. I look down on you imperial peasants with my superior metric system.

[@Lord.Smith.the.first.]

My father says that! I was always confused about it 😂 , I'm a virologist and I could not be a machinist in a million years I've investment cast my own jewllery but fine machining is art form to me

[@AppliedScience]

Really really interesting video (like all of yours)! I had no idea about the 1d and 3d difference of speed of sound. Thanks so much for sharing your curiosity and experiments with us!

[@AlphaPhoenixChannel]

Yo nice to see you here! Glad you liked the video! the extensional thing was new to me as well. I assumed it was actually like, pulling on a bar, "extending" it instead of compressing it and ignored that number completely at first. Feels like for large displacements, the interatomic potential IS asymmetric, so I bought my own assumption far too well... guess I should have figured out what it meant to start!

[@MSI2k]

Wow, all the big names are here!

[@norwegiansmores811]

might be stupid of me to say. but would it not simply be that the "delay" would be the same on both ends? and that once you overcome the intertia both ends move at the same time after the 1 second delay? Meaning. the speed of "push" can not be obtained on the object until the delay time which for all i know could be either light or sound speed has elapsed. on a perfectly rigid solid object there would be a delay on both ends until that time has passed both ends will travel in the same direction is basically what my theory is. il try one more time to explain my thought process.. You cannot overcome the inertia of the object on either end until the time delay has elapsed

[@shoo7130]

My gut impression was that if the material is not constrained around the outside, then it behaves in a more elastic manner. It has more freedom to compress by expanding sideways, which is harder to do if there's more of that dense material in the way.

[@lyricsassam]

@@norwegiansmores811 my thoughts exactly, I still don't believe that "motion" takes such a visibe amount of time to travel in such small dimensions. Maybe there'd be some actual motion delay for lengths in the range of 10⁸. But yeah, totally agree on the inertial delay part

[@jakesazgari9201]

At first while watching the video I said to myself “I wish I could see his trial and error process for this experiment” and was pleasantly surprised when he actually did. Well done.

[@mcreedican]

The details and mistakes are really the best part of these types of videos, I roughly knew the answer but I would not have guessed the problem with the piezo sensor having so much squish varriance.

[@ObeyCamp]

Man, KZbin has really been slacking with my recommendations because this is the first time I've seen your channel. I've always wondered about this exact thing but never had any way to find out for myself, and never even knew quite where to start vis-a-vis googling an answer. This video was such a satisfying vindication of my curiosity. I subscribed right away!

[@RovingARock]

I loved the "electrode clipped to hammer" solution - I didn't think that was messy at all. Great solution!

[@orangequant]

Yes. But I was wondering about the delay for current to pass from hammer head to hammer claw, and the electrical spark gap in advance of hammer head "actually" contacting the rod. Anyway, speed of sound never occurred to me as part of any viable equation- I thought of it all only as a Young's modulus problem of compressibility. Looks like I was mistaken.😆

[@Layarion]

@@orangequant ya i too was thinking about the spark starting the hamTimer a bit sooner than it should.

[@antonliakhovitch8306]

This reminds me of a method of auto-levelling cheap CNC machines for PCB manufacturing. You just attach an electrode to the bit and another to the PCB blank, so the machine knows when it's touching the blank.

[@sarowie]

@@antonliakhovitch8306 contact milling to precisely get to an inner layer of a multilayer board is also a thing.

[@orangequant]

@@Layarion so I am not alone!

[@Cybermyrc]

I wanted to comment and say I'm really glad you added the section at the end where you went over how you were getting the "wrong" results back during testing and why they occurred. It's a part of science that doesn't always get talked about often, but is easily one of the most important.

[@dametocosita4994]

Then do it

[@praneelbhagavatula7680]

@@dametocosita4994 do what

[@dametocosita4994]

@@praneelbhagavatula7680 comment

[@dametocosita4994]

🤣🤣

[@Dekoherence-ii8pw]

0:00 There's obviously going to be a compression wave which travels at some rate that'll be quite a lot less than the speed of light. EDIT: Oh and that IS the speed of sound.* *speed of sound in metal, which might be different speed of sound in air. Because a compression wave IS sound!

[@SkyhawkSteve]

I was so happy to see that you validated your test set-up by testing a range of rod lengths, and then graphed the results to make sure it made sense. As an engineer, I've had to learn the hard way to not just trust that your assumptions are correct. 🙂

[@milantrcka121]

"Trust but verify!"

[@SteveMould]

Really great video!

[@oem42]

Damn... The gangs all here

[@renedekker9806]

You know you have made a good video when Applied Science, Practical Engineering, and Steve Mould all comment on it. 👍

[@zimboiii9025]

@@renedekker9806 Life goals

[@lyricsassam]

@@renedekker9806 and the Incroyables Experiences guy is also a science youtuber. So yeah multiple wins

[@jawms]

You just like it because of the springy atom model.

[@bramvandermallie2229]

I am a metal worker and I often ponder this when striking a large piece of metal with a hammer and how the noise is generated. When I saw a 1000fps camera watching a drumstick hit a symbol I then realized that metal is kinda like a jello ! this further grants me a deeper insight into the nature of the materials that I craft with. Thanks a ton! Now I have questions of material hardness like mild steel vs machine steel or hardened? Answers always leed to more questions, I am grateful for people with such a wealth of knowledge and perspective that can break this stuff down for simple minds like mine.

[@bunnykiller]

if you think thats kewl, ponder the different sounds that are produced by metal in the many different applications... such as the guy lines holding those 500+ foot tall towers, the round rail track a crane pivots on, really long metal pipes of various diameters... they create sounds that are very strange to just hypnotic.

[@KitagumaIgen]

Harder materials - higher speeds of sound (typically, strange stuff "always" appear).

[@brunogausa]

@@KitagumaIgen not actually. What you meant is that higher *rigidity* implies higher speed of sound, wich is the magnitude de Young modulus measures. It's a property of the material, hence it is not afected by heat treatment of the steel or the alloy. There is a beautiful video from This Old Tony where he explains that in a lovely way (it's also fun). Cheers!

[@KitagumaIgen]

@@brunogausa Do you have some example where a harder material doesn't have a higher Young's modulus?

[@brunogausa]

@@KitagumaIgen well, a clear example is the comparison between hardened amd mild steel. Other cases are harder to come by, but there are materials like poliurethane resins that are not as hard as steel and more ridgid. It's an interesting topic

[@GregHassler]

"All models are wrong, but some are useful"

[@MadMan-r5s]

But some are less wrong

[@lumpyspaceprincess6335]

​@@MadMan-r5sor less representative

[@derekschmidt5705]

​@@MadMan-r5s Those are the ones that are useful.

[@Ethan13371]

Is that a model?

[@arthurmoore9488]

@@MadMan-r5s Yet, as noted in the video, the more accurate the model the harder it is to work with. As alluded to in the video, the more computational power is needed. There's some interesting discussion about modeling wooden structures, like bridges. Just due to how things end up working it's normal to simply assign a beam x/y/z material properties. Yet said beam might actually be a laminate, and wood itself is not uniform. I might be mistaken, but I don't know of a commercial CAD simulation package that takes wood grain direction into account.

[@gardenofadam79]

The only experiment I need to see is “Can one make a Fing-Longer long enough?” Great video as always. Thank you for putting these concepts we often see as theoreticals into practicals!

[@AlphaPhoenixChannel]

I need a what-if machine

[@jmacd8817]

@@AlphaPhoenixChannel but wouldn't that entail the need for an if-than-else machine? Or, at the very least, an oh-crap-no! machine

[@mrosskne]

what's a fing longer?

[@stumpybumpo]

@@mrosskne its the glove at 3:44

[@zyeborm]

@@AlphaPhoenixChannel do you speak French?

[@kaksspl]

I really like the inclusion of troubleshooting at the end. It humanises the experiment and the work behind it. It's inspiring in a way.

[@scoreunder]

Going to give you my guess here: C, speed of sound. I'm no physicist (graduated in computer science) but my gut feeling says "somewhere much lower than the speed of light" -- atoms have to propagate repulsion along the entire length of the bar, which is something mostly "one after the other" -- and I had completely forgotten that a term, "speed of sound", already exists for what is pretty much the same phenomenon. I do wonder if the strength of the impact affects it, because pushing those atoms closer together would generate more repulsive force in response, which would mean greater initial acceleration for the next atom in the chain. However that would have the consequence that louder sounds -- or even just higher-amplitude components of a sound -- travel faster than quieter ones, so that would be a surprising result to me. I'll watch the video and see what happens :)

[@stewiesaidthat]

on Mars, low-pitched sounds travel at about 537 mph (240 meters per second), while higher-pitched sounds move at 559 mph (250 meters per second)", concluded NASA.

[@DanKaschel]

My intuition only came after learning the answer unfortunately: the speed light applies to energy waves propagating through a medium; the speed of sound applies to the movement of the medium itself.

[@lgbfjb7160]

Speed of sound through the solid, which is faster than through air.

[@admthrawnuru]

This exact concept blew my mind about 15 years ago, but I never saw it actually demonstrated until you did it here.

[@thethoughtemporium]

Love the setup. Very simple and clever. Great demo!

[@slipsonic809]

Some interesting thoughts I had about a 300,000 km long steel bar in space: If you were floating there with it, it would look like a small diameter steel bar but you wound not be able to move it by hand due to the mass of it's length. It would feel like an immovable object anchored on nothing. I guess it might bend on a large radius but snap back when let go. That would be a very weird thing to see. Also, a bar that long of the diameter shown would drift around like a soggy spaghetti noodle if other forces like gravity were there acting on it. It's too bad we can't have a very long steel bar in space to see how it would behave first hand. edit: also want to add that the effect of heat and cold on a steel bar that long would make for massive changes in it's length. Railway operators sometimes need to heat up rails in cold weather because they shrink so much and create a dangerous gap between rail lengths. If my math is right (please correct me if I'm wrong) a 1 degree c increase in the entire length of a 300,000 km long bar would increase it's length by over 3000 km. Insane.

[@TheRadiastral]

You wouldn't be able to move the whole rod, sure, but you could easily shake or bend the end of it. And, as you said, it would most likely just snap back and vibrate for a long long time. You're spot on regarding the contraction/expansion due to heat. Frankly, any sudden change in temperature, like it emerging from a shadow into the light of a nearby star and that rod could literally impale an astronaut or a spacecraft, unfortunate enough to be nearby and in its path. It would be a very very weird sight indeed. I suspect, at such length, other physical effects might manifest that we haven't even thought about.

[@Thedamped]

The value of 3,000 km expansion for a 300,000 km would be 1% per degree, that seemed high (100°C change would be 100%). So, I found a document listing steel's expansion from 0°C to 82°C being 1.34 mm / meter. So that's 402 km for the entire range or about 4.9 km / °C. Though apparently different types of steel can vary considerably (by about 50%).

[@Pixelarter]

Also depending were the bar is in space and how it moves, it may be influenced by magnetic fields and get an induced electric current on it. If you touch it you might get zapped, or the bar could be very hot, or the steel could burn and snap like a soldering stick.

[@TheRadiastral]

@@Pixelarter Very true, I was thinking about this too. In a way, it's a giant antenna and will convert any radio signals hitting it into electric currents, zipping back and forth along the length of the rod. Getting zapped by it would indeed be a real concern, in my mind too. Then there is the magnetism of a steel rod, which could cause it to change shape and attract/repulse other magnetic objects around it.. It's a mindfield haha.

[@scrambledmandible]

@@TheRadiastral Nanohertz communication

[@garrinbentley9605]

One of my favorite things about this channel is that it understands that the vast majority of the time we use shortcuts so that we can actually do something with the data, so many people seem to forget about this when they scale things up

[@coltentackett892]

I was talking with a man that builds oil facilities and he was talking about how when they're drilling a hole into the earth If they have a few miles of drill stem out and they run into a cave, the entire drill stem will lag a little bit like a slinky. He said the loads can be upwards of 1million pounds falling 10feet then stoping at the bottom of the holllow spot. Incredible.

[@fmr1998]

This is easily the most underrated channel on yt. The explanations are, as always, very on point and easy to understand. Keep up the great work

[@73xlh]

I disagree. This was my first and only vid to watch here and 2 seconds in, I was so annoyed with this guy I had to turn it off immediately.

[@jhcoverdrive9287]

Definitely agree. It’s good to see other big name science channels in his comments. Even better to see his view stats going up.

[@IncroyablesExperiences]

When I was young information was less accessible and it has been a mystery for years, I was pretty sure it was possible to transfer data faster than the speed of light this way. Nice video.

[@JarutheDamaja]

Well it proofs that it's not possible with iron. Maybe it's possible with diamonds or some material 10 times stronger than diamonds. (Where the atoms are more "stiff")

[@user255]

@@JarutheDamaja No, the interactions between the atoms still have the upper limit of the speed of the light.

[@tetramaximum]

The speed of light is also called a speed of causality. It's impossible to be faster than this speed.

[@alysdexia]

faster -> swiftlier; not nice < niais < nescius := not-skilled but you are: -> well

[@LachanceM]

@@tetramaximum It's the fastest speed the processors of the simulation we live in can run at. If you break the speed of light, the thing blue screens.

[@JohnClulow]

This was without question The Best science video I've ever seen on YT. ( I'm a retired chemist / materials scientist from the thermoset composites industry.) And it's the process you recount that makes it so, and, of course, the joy of discovery that we finally see happen. I think it should inspire young people. Well done!!!

[@davidderidder2667]

This is how Physics teachers should be teaching kids.

[@JackOusley]

It’s really cool that you were able to measure it with such a short bar

[@geekygamer3954]

Everything is a spring. In this case, the bar has a really low spring constant. Instead of compressing the spring, you move the spring entirely. The force travels from one end of the rod to the other as a (fast) speed determined by subatomic particles, the rod compresses, then it transfers its force from the end of the rod to it's target.

[@CalculusPhysics]

i think u might mean really high spring constant, but ya!! and actually the Bulk Modulus is basically the spring constant for solids :)

[@shadrach.indigo]

as a physicist, "everything is a spring" was my first instinct lol

[@yearswriter]

Man, this channel is one of the best channels there are. Great video.

[@bbqchezit]

15:18 This is the best part of the video by far. I learned an interesting concept with your demonstration, but so much more practically about your thought process when reviewing concept to fruition. You learn so much context just troubleshooting your setup, questioning your sensors and methodology. I love that you share this part with every project Guess it just goes back to the motto that "Plan A always goes up in flames" :)

[@alistairmackintosh9412]

Actually, plan A just sits there, it's plan B that goes up in flames...

[@CaseyW491]

This is awesome. People forget "the speed of light" isn't just about light. It's the speed of causality. The quickest information can be transmitted. So no matter what, even if there were NO space between atomic structures (assumingly existing in theory only), that's the fastest possible speed. Edit: As soon as you hear the term "wave function" to calculate any option, that should tip you off right away that it's not instantaneous. Love the ball/spring model!

[@someverycool4552]

It makes me wonder whether it's misleading to teach it as "speed of light" in the first place, as it should just be a fundamental maximum speed of causality like you said. Speed of light is just one manifestation of it.

[@NightmareQueenJune]

I really respect your ability to explain such concepts easily. That's a trait not everyone has and it's really valuable.

[@jeanladoire4141]

As a blacksmith i must say i'm always very interested to know how energy travels trough the steel, the hammer, the anvil etc. Nice video!

[@v44n7]

upload some videos of your work!

[@777rev]

Yeah bro upload videos

[@jeanladoire4141]

Maybe i will eventually, but idk i like explaining stuff and discovering new tricks but not editing videos

[@PopsGG]

This is exactly the kind of content I love. Questions that seem so simple, but are complex to answer and the answer is not commonly known. The kind of questions a curios child would ask, but no one knows the answer.

[@molybdaen11]

Questions like : why does the arrow moves forward if I let it go from the bow?

[@TheRyujinLP]

And this is why HEAT rounds are so effective, the penetrating jet is moving faster then the speed of most known materials. Basically the jet is punching through the material faster then the material can even react to it happening! Of course once you do that the material stops acting like a solid and more like a thick molasses. At this point normal material properties stop meaning anything and penetration starts getting close to the idea penetration model where the jet is going to penetrate a depth equal to the square root of the ratio between the destiny of the jet and the density of armor (this is part of the reason a high density metal like copper is used, it's about 14% denser) times the length of the penetrator. Notice that last part is linear. This is the second reason copper is used, it really ductile. You can pull it into a really long and thin wire before it fails. This means you can get a nice long jet of it, the longer the better! This in turn why you hear the idea of "fist to finger" brought up with HEAT rounds. The greater the rounds diameter, the more copper you can have which means you can get a longer jet before the copper breaks up and since penetration is linear with length, all thing being equal the bigger warhead is point to punch a proportionally deeper amount of armor. Now with all that in mind, this also part of the reason why modern kinetic energy based anti armor rounds (though technically, HEAT rounds is a type of kinetic energy weapon... it's just a little more complicated... as long as my rant above is, I left out a lot) use what looks like thin, really long darts. While they don't hit quite as fast as a HEAT round, they do get close enough that the extra length does aid in penetration. Long story short, the science of material handles impacts at really high velocities is really neat. And this should also give you and idea of would happen if you tried to push a light second long rod of metal.

[@victorandrei02]

Wow this is great. I can remember the day when my thinking finally made the switch from thinking about science/engineering and it's equations as a form of truth to rather a set of useful models that we've made for our universe. The earlier you make the transition, the better, so I really think this is how science should be pushed to students (probably no earlier than high school.)

[@kaikart123]

bUt iT'S a LAw

[@retsaMinnavoiG]

To be fair science does not claim to be the 'truth' and is not taught that way. The foundation of science is the scientific method and it makes it abundantly clear that we just interpret results to decide whether those results are accurate. There is no truth.

[@ClubPenguinBand1]

I've wondered about this for YEARS. Ever since Gavin Free (from Slow Mo Guys/Rooster Teeth) asked "what is the speed of push?" on a Rooster Teeth podcast. They all made fun of him, but I was thinking "..thats a good question." I dont have to wonder anymore! Great video

[@janmelantu7490]

Re: bar speed: I remember Veritasium talking about it taking the speed of sound in the object. It was how shining a(n idealized) laser at one edge of the moon, and then flicking the laser point across the moon to the other makes the dot go faster than the speed of light. Nothing is actually going FTL (the dot is just an image), and if you tried it with a solid rod (I believe it was a wooden plank in his version), he said it can only travel as fast as the speed of sound in the object

[@dexorne9753]

Imagining that the blank would be unbreakable, I'd assume the plank would move kinda like a whip, and it would probably crash reality or some shit.

[@janmelantu7490]

@@dexorne9753 an unbreakable plank would almost certainly stretch out considerably across the diameter of the Moon

[@bengoodwin2141]

@@dexorne9753 if it is unbreakable then it can only bend, otherwise it would break physics. It could approach the speed of light but not reach it in this scenario.

[@stylis666]

@@bengoodwin2141 Exactly, and the time it takes before the other end starts moving after you move your end is determined by the speed of sound through the plank, which would've given us the correct answer because that's intuitive when you think of a plank bending. It's not as intuitive when you think about pushing the plank inward, but motion is motion. It's so obvious in hindsight :D AphaPhoenix just made the puzzle harder on himself by not just wondering, what will happen if I get a really big sharpy and write my name on the moon? :p

[@Suresh-ml-raghavan]

Excellent video. You nicely take us through your thought process as you iterate between your experiments and theoretical calculations. This is one of the better videos to help highlight the experimenter’s burden and will be worth watching for budding experimenters in all science and engineering, not just material science. I’d like to point out here (and likely others have too - I haven’t gone through enough of the comments) that though you started out seeking to use experiments to get the right answer, you (likely inadvertently) switched your objective to making your experiments agree with theory (some theoretical formula; any theoretical formula) because that is what would convince you that your experiments are precise and accurate. I’ll certainly agree that the fact that the final experimental numbers did agree with the most seemingly appropriate theoretical formula (longitudinal or 1D rods formula for speed of sound) suggests you may well have gotten to the accurate enough and precise enough answer to your question. But this approach (of ‘fixing’ your experiment until it agrees with one theoretical formula) only works when others have already done the experiments and have reached a consensus and you are trying to replicate that as an amateur (no offense, I mean it in the most respectful sense) for KZbin viewers. This approach is not adequate for actual real world experiments in the scientific world where we seek to truly ‘test’ theory. Often yours would be step 1 - make your experiments as precise and reliable as possible by testing against previously established theory and THEN start acquiring truly new data to test new theoretical ‘formulae’ or ‘models’ that extend into unchartered territory. Anyway, kudos for an excellent video. It reminded me of the saying, ‘No one believes theoretical results except the person who performed the theoretical calculations; everyone believes the experimental results except the person who performed the experiments’.

[@himselfe]

Even though I came into this video knowing the answer was the speed of sound, it was still fascinating to see it experimentally demonstrated and be shown the theory behind it. It's one thing to _know_ the answer, it's another thing to *understand* why that answer is correct. I love videos that elucidate concepts like this. Great job!

[@losboston]

Nice! My fave thing, philosophically, that you said: "I love it when...the underlying mathematical machinery can be recycled." A close second, "Almost every physics model...is technically wrong." That our understanding of the world is really just a collection of imperfect models, but that the models of the different phenomena share mathematical pattern, is the basis of successful engineering, and kind of astonishing. My fave practical thing is the illustration here of the impact of ratios on the validity of models. In this case the small radius to length ratio allowed for the 1-dimensionalization of the model, simplifying it and the math, and it was accurate!

[@princetbug]

either c or d. since the speed of sound is based on the rate at which a wave travels through particles, that makes the most sense to me as having relation to this problem. though the amount of force applied and other constraints may affect it as well. I'm not as well versed there

[@eeach]

Yeah, I figure it's the speed of sound through steel... which, I think is what d is getting at.

[@jfbeam]

Exactly. If you hit it hard enough / fast enough, it will "mushroom", thus not transfer that energy through the entire bar. (in this bench experiment, you'd break the hammer and sensor before getting to that point.)

[@ChicanaLoca1315]

I can’t believe i’ve never heard of your channel before! You’ve earned my subscription, and i’m excited you have an assortment of videos in my queue.

[@viniciusmmd2282]

12:00 it's interesting to thing that real springs are made of atomic electromagnetic springs

[@LeRainbow]

Your videos are always so well researched, well thought out and your demos are top notch. All the while the editing is there, too. Thanks for all the work you put in and not cutting corners! It really makes a difference, I love learning about the basics again as too many times we think we are too smart for our own good. I just last week had to re-learn bernoullis equation to understand again how energies are distributed in fluids within closed loop systems; something I always thought of as an easy basic - living is truly constant learning.

[@arnavwadhwa9014]

Everything about the video is so epic! Script, the production and obviously the content! Channel is so under-rated. Deserves like atleast a few million subs

[@jonathanbailie]

I love your explanations of the physics. Brilliant job on the experiment, so interesting!

[@ashurean]

I can't say I'd ever thought of this before. On some level I understood that every solid object was just individual atoms bonded tightly together, but I never really considered how applying force to one side meant that the force had to propagate through the material. Edit: Coming back to this a year later having forgotten about this video was interesting. I've definitely internalized what I learned from this. The model I had for this situation in my head was a lot more accurate and I more or less thought it out step for step with how it's explained here. Very satisfying.

[@Propane_Acccessories]

Ever think about a seesaw that is a lightyear long and what would happen if a weight were placed on one side?

[@DustinRodriguez1_0]

That was amazing. I was always annoyed in school when details like this were glossed over. It's like how I get annoyed when people say the speed of light is that constant 300km/s. That's true in a VACUUM, but not in other materials. Same with the "speed of sound" which always has the speed of sound in AIR priveleged as somehow special, when in reality it varies in materials by a tremendous amount AND has huge consequences. These things being glossed over does not benefit us, not even when we're kids.

[@JarutheDamaja]

The question is, what would happen if both ends are pushed at the same time? Both ends would travel "inwards" then the 2 waves would collide in the middle and a few hours later both ends would snap back?

[@bengoodwin2141]

@@liam3284 I don't think this is accurate, the bar wouldn't expand, it would exert crushing forces inwards at the middle, like squishing a cube of jello on two ends or something

[@memyname1771]

@@liam3284 Even an easier to see example, fill a bowl with water and stick a finger in each side of the bowl to generate waves. You can see the waves pass through each other.

[@Randy14512]

You can use a Newton's cradle to see what happens...

[@ExaltedDuck]

The title question was answered in the first couple seconds. When you hit the steel bar with the hammer and it went 'tink tink' instead of 'thump thump'... that was exactly the motion you were talking about, setting up a standing wave in response to the shock of the hit.

[@ashlardarned2540]

Thank you for going over your methodology *and* the problems you had in setting up your test apparatus to eliminate error *and* how you realized you were getting the wrong-right answer!

[@skyhop]

This is one thing I think about a lot relative to high velocity explosives. The way they instantly shred very dense materials into tiny fragments. I assume this is due to out-running the speed of sound in the material.

[@ToriKo_]

Woah wtf

[@rogerm3708]

When an object strikes another object, causing a spark, for an infinite moment are both objects traveling at the speed of electricity?

[@graealex]

I was always under the impression that the speed-of-sound is the intrinsic "speed of motion". If you tap the end of a pole with a hammer, that will dictate when you can first hear the tapping on the other end of the pole. Although that can't answer the question fully, as it is obviously possible to move stuff faster around than the speed of sound. Also: DSOs are really a marvel of economies of scale. You can basically buy scientific equipment for only a few hundred bucks that will show events in the ns range. Maybe I should clarify: a high-explosive for example isn't limited by the sound of speed. In fact, any shock wave travels faster than the local speed of sound of the medium. But that's something for AlphaPhoenix to explain.

[@EmanuilGlavchev]

That's where a still initial frame of reference kicks into place, I guess. The speed of sound in a material matters in reference to the material itself. since the pole was initially not in motion in our chosen frame of reference, the squish traveling through it maintains the 5100 m/s or w/e it is relative to the still piece of pole still ahead.

[@graealex]

@@EmanuilGlavchev That's clear, but doesn't explain the shock wave problem. Unlike the speed of light, the speed of sound isn't really an intrinsic upper barrier here. It's just the speed the material likes to pass a wave on if no one forces it to do it any faster. But if you detonate a high explosive next to said metal rod, it's not like the rod has time for transmitting that wave at just the speed of sound. And the rod isn't infinitely compressible. I mean there are papers on it, but they're beyond my understanding of the physics. It's not very intuitive for me to understand what is actually happening if you push the rod at speeds exceeding its speed of sound.

[@FlorianLinscheid]

I think I can resolve that pretty easily. Your first impression is correct. If you tap one end, it will take l/c until you hear it at the other end (if you take the correct speed of sound etc). But the speed of sound is defined for an elastic wave. Which basically means no huge forces, which break the material (over its yield strength). Yeah you can tap on the steel rod faster than its speed of sound, but then you permanently deform it. Which is in a way what happens to air as well, when you break the speed of sound in air. The speed of sound isn't a physical speed limit like the speed of light. It's the velocity that an elastic wave travels. Also there are longitudinal and transversal speeds, which happen of course simultaneously and make the wave propagation a mess.

[@graealex]

@@FlorianLinscheid I'm not really convinced the rod is necessarily getting permanently deformed if I hit it with a hammer swinging at 10 km/s. Obviously the hammer would try to push material faster out of the way than the material likes, but is the explanation here really "it just breaks" and that's it? There surely is a gap between the speed of sound and the speed of no-compromise breaking, no?

[@dsdy1205]

@@graealex So if you accelerate a medium at speeds exceeding the speed of sound, you create a shockwave in that medium. This is true for air, metal rods, and whatever material you care to analyse. The shockwave can travel faster than the speed of sound in the medium, but only so long as energy is supplied to it, for example by the presence of a large mass of gas / whatever moving at supersonic speeds behind the shockwave. Absent this energy it decelerates to the speed of sound and becomes effectively a sound wave.

[@Strunz0]

So about 15 hours for the observer to see this rod move at one light second distance away. This really offers some perspective on the difference between the speed of light and speed of sound

[@xenten9686]

My instinct was right in that in order for the material to move the atoms would have to get closer and then be repelled by their electrons; However, it never occurred to me that this nature of atoms getting closer and spreading apart is what sound is and that by proxy it would travel at the speed of sound. Very great video!

[@busttoboost]

But isn't that force that keeps these atoms and electrons "fixed" in place enough to carry that momentum instantly? Or am I overthrowing it and not realizing it would basically be a Soundwave moving through steel?

[@ShinyKelp]

That's quite a SOUND argument

[@xenten9686]

@@busttoboostWell the force is inversely proportional to the distance between the atoms that means that a given aton would accelerate the next in line slowly and not instantly. This time it takes to accelerate and deccelerate would be the wave of sound travelling. Or in this case the wave of movement.

[@martinnoll7647]

@@busttoboost I was thinking about the same problem here. The speed of the impacted force is traveling with a small decay, depending on its material structure. For example, hitting a sponge would take more time for the atoms to carry the momentum the the opposite side, a metal bar on the other hand would transfer the impact almost immediately, because of its dense and hard structure. Now the theory: if an object had absolut zero plastic deformation on impact, would it transfer the information, or in our case the force, immediately? So faster than light? Of course in reality, finding such an object would take a bit of time, although im not an Physicist im quite curious if this theroy is possible in some way.

[@mikess308]

So what happens if an object hit it at say mach 2 with no deformation or energy loss between the 2 materials?

[@davidevans2673]

My son actually proposed this very same thought experiment to me when he was about sixteen and wondering about the speed that information can travel. Great minds think alike! This fall he will be heading off to university to study mechanical engineering. Thanks for sharing this brilliant experiment and explanation.

[@MrZapper1960]

When I was a kid I used to always ponder this question as well as whether or not two objects really could “touch” each other. Fun to see a video like this

[@livebungusreaction]

The two objects touching blew my mind I remember squeezing my fingers together and thinking if you kept zooming in as you went down they would never touch and it blew my mind and I desperately tried to discuss it with my dad and he didn’t understand. Thanks for unlocking a super weird memory for me lol

[@gl2814]

exacly the same experience here.

[@edwinov]

It also means you can bitchslap whomever in the face and get away with "I never touched him you honor!".

[@speedy01247]

I once wondered what would happen if you could make a infinitely dense object into a bar or just a line, then push it, it's infinitely dense so there is no space between anything so shouldn't it instantly move on the other end? I have no degrees, its just something I'm curious about.

[@reedy_9619]

@@speedy01247 Wouldn’t an infinitely dense object have a null volume? Like a point. If it’s a single you can’t really measure its ends. It’s instantaneous but the pressure wave doesn’t travel any distance. I think it would make it’s sound speed undefined too. (0m/0s) My opinion isn’t worth much im not great at maths or with physics.

[@michaelclarkj]

The trial and error end segment was absolutely brilliant. The whole video is fantastic.

[@dtmrea247]

Years and years ago I had to explain basically this to a guy in a youtube comment who was trying to imply that physics (maybe just astrophysics) is bullshit. His example was a very long tube with golf balls lined up inside it - that pushing in a new one would mean that the one at the other end of the tube would fall out instantly, and therefore the speed of light being a cosmic speed limit was bullshit. I reasoned that, first of all, you'd need to apply a shitload of force to push millions of stationary golf balls - and then since you're applying so much force, that will clearly compress the golf balls, and you'll have a pressure wave moving through the balls which would likely be very fast, but decidedly slower than the speed of light. I think he then got mad.

[@obsideonyx7604]

Sounds like a SJW. Did they try censor and cancel you after they got triggered?

[@tightbootyhole707]

WHAT?!! ARE YOU TELLING ME PHYSICS ARE RACIST? im joking ofc

[@QuesoCookies]

@@obsideonyx7604 Lolz, how easily triggered do you have to be to imagine SJWs in scenarios with nothing to suggest one might exist. You're not even a snowflake, you came to the table pre-melted.

[@obsideonyx7604]

@@QuesoCookies observation = triggered Nice logic

[@QuesoCookies]

@@obsideonyx7604 Speculation =/= observation Logic 101

[@cslloyd1]

Fantastic video! It was great hearing about the problems you encountered in measuring this - that really helped.

[@davidistvankis8466]

As a metallurgical engineer, this was new stuff, even for me :) By the way, explanation of the atomic structure and Young modulus is super correct! I will try to make this demonstration to my students! Thanks a lot🤚

[@shikhanshu]

This video was VERY interesting to watch. I didn’t learn much of anything new as such, but how it all came together is fantastic!!

[@lijkenkist1]

This was the most fun I've had watching a scientific video of any kind. I'm a mechanical engineering student and have always been very interested in macro level material science. You explain your thought process and methods in a way that is very pleasant to listen to. Earned yourself a new sub!

[@frostbird3431]

More physics stuff!! :D I love your very solid explanations

[@jaspervandenameele4834]

Is it solid though :o

[@AlphaPhoenixChannel]

@@jaspervandenameele4834 ooh gottem

[@SahilAggarwal1997]

this guy deserves way more subs. Kudos for the content you are making.

[@metilaful]

I agree

[@schizeckinosy]

I regret that I have but one sub to give to this channel

[@thegibusguy4969]

You speak with so much passion and it's really engaging to listen to!

[@kencoleman7762]

I am enjoying these videos immensely. My undergraduate degree in physics is 52 years old and we didn't study any of this. Keep 'em coming and I'll keep watching.

[@RoflcopterLamo]

@@cosmicpeoplespacerock7930 Bad bot.

[@stesala]

When I was a kid, thinking of the constancy of c, always thought that a mechanical arrangement (without any play) would easily violate that constant, being the motion transfer instantaneous. Then thought about it in the years and I realized it couldn't be the case. You demonstrated it in the neatest way ! Good job.

[@2adamast]

It's weird that kids have a better hold on einsteinian relativity (or quantum physics) than basic mechanics like hookes law

[@XtremiTeez]

How many years ago did you first think of this?

[@stesala]

@@XtremiTeez don't remember. I think I was 8 or 9. But remeber my father told me once that superluminal speeds were impossible, without a thorough explanation.

[@XtremiTeez]

@@stesala because I posted something about this 25 years ago.

[@stesala]

@@XtremiTeez no. Internet wasn’t a thing at the time 😀

[@eraelas]

Very interesting. I had actually been wondering this exact question like a year ago. Glad to know the answer now. Never figured it would have to do with the speed of sound through the object. Neat.

[@lucasrem1870]

the pressure sensor is not that fast, 180 ms

[@banton9368]

It really took me most of a-level physics (16-18 yrs) to understand the concept of what was really happening when two solids collided. Like I vaguely understood that atoms had bonds forming molecules, and molecules couldn’t occupy the same quantum state as each-other, but learning about how it’s photons that transfer kinetic energy and not just a particle bumping into another particle seemed to make so much sense when I first heard it. That’s probably one of the reasons I’m know trying to complete a degree in physics, because I finally understood a concept intuitively that really seemed convoluted at first. I think it’s very similar to the reason I first became interested in learning anything whatsoever. I will never forget my year 2 teacher miss goody (when i was 8-9 years old) who left the school but left me a note saying to never stop asking such great questions.

[@kehrnal]

This was truly beautiful. Thank you. I've theoretically understood this, but never quite wrapped my brain around it. This was a wonderful demonstration. I hope you have plenty more projects planned for that oscilloscope because it does wonders

[@AlphaPhoenixChannel]

Ive wanted one of my own since high school when I first played with an old analog crt scope. They’re beautiful tools

[@HeavenlyDemonicKid]

Damn, this is really cool. I like the way you set up the experiment and could explain the concepts simply enough for a layman to understand, but also include enough detail for an engineer when needed. Definitely worth the subscription

[@Sollace]

2:00 I'm calling it now, it's going to be C, because the mechanics we're dealing with here isn't dissimilar to how sound waves propagate though air. The bar doesn't all move as a single object; the bar experiences a compressive force that moves through the object in form of a wave. The first row of atoms experience the force at the point of impact, they move forward, then transfer that force to the next row of atoms, and so forth until the entire body has been carried forward. The propagation is only faster in the solid because we're dealing with smaller distances between the atoms, as they are packed more densely. Other than that, it works exactly the same as it would in a fluid or gas.

[@LukePN]

I love this channel. I majored in physics, and used oscilloscopes for validating clock synchronization timing to nanosecond resolution. I feel like this channel is specifically made for me :-p. Oscilloscopes are amazing, and you are so clever at finding ways to leverage it to show some phenomena that is otherwise almost impossible to demo outside of models or using very specific lab setups. Your video asking what happens when electricity meets a fork with one disconnected side should be required viewing for 200+ level physics students.

[@sanches2]

worked on a very similar problem a while ago, things get really hard really quick. had to measure energy of impact of cordless impact drill used 12Gs/s DAC and custom amplifiers. The model is really close to a RF transmission line :) the speed of sound and the temperature are the main factors. i have recordings of the wave travelling through the rod and the losses at different crossections due to emitted sound and plastic deformation. it was so cool :)

[@DrArtiePoole]

Solving the speed of sound equations in 3D crystals is a very well documented process and yet it still remains very challenging to solve for the elastic constants in the materials I study... Very interesting how the crystal symmetries play a part in speeds of sound.

[@benjaminjoeBF3]

it should be faster right?

[@simontist]

Does it depend on the angle? Also what about pressure vs shear waves? Very complicated, moreso than in fluids.

[@ankurage]

As a mechanical engineering student I can confirm that compressible fluids are one of the hellholes of fluid mechanics and thermodynamics

[@vlogcity1111]

Do it bring a lot of variables that come with it?

[@thecompanioncube4211]

Also as a FEA analyst Speed of sound through metal is the bread and butter of all the computations and basically make all the modern stuff around us work

[@eljuanman999]

@@vlogcity1111 not only that, but the relationship between them (the equations) is more complicated too

[@ianallen738]

@@vlogcity1111 Yeah but the real problem is that is where the additional terms in the equations drop off into infinity and often cannot be solved even numerically.

[@devd_rx]

@@ianallen738 yes this. I hope someone comes out in future to solve this problem

[@richard--s]

My guess is (c), it depends on the speed of sound (in that metal!), until the other end of the bar moves. Because it's about a physical movement. And sound waves are physical movements. OK, let's see where I am with my guess ;-)

[@theendofit]

This has some intresting implications. Especially for the fact that this means this is much more observable. We could make a mile long steel bar and have a machine push it. It would take a whole second. With a slow mo cam half a mile down we might even be able to see the ripple of the movement

[@DrakonIL]

A mile long steel bar at 5/8" thick would be around 21,000 lbs. A slow mo camera could see the ripple in the 91cm bar. No need for the super long bar.

[@MultiMinecraftPiggie]

I'm about to graduate from university with a materials engineering degree. Keep up the great work, videos like this will really get more people interested in our field :)

[@StrengthScholar0]

I always wondered about this. I knew that transfer of information couldn't happen faster than the speed of light but I could never wrap my head around why it wouldn't work with an incredibly solid low weight materials like carbon fiber or graphene. To think it was predicted by something as simple as measuring how fast sound travels through the material blew my mind. thanks!

[@crazyrocket2900]

18:16 you took my comment idea! I was about to suggest it could be something where you had a different alloy than the website was using since I imagine that (since so many properties of steel vary based on the amount of carbon) the speed of sound must vary a good bit depending on the type of steel. That's really cool how the speed of sound varies based on the "dimension" of the object that you're compressing and that a really thin bar will have a different speed of sound than one that would squish outwards a little bit.

[@lucasmurphy6187]

Man this takes me back, did almost the same experiment way back in my Mechanics of Materials lab in school. Its not too often that I hear people talk about strain wave propagation, so I really enjoyed seeing this.

[@Wolforce]

I guessed C but I was secretly hoping I was wrong and weirder stuff was happening. What a great video :) keep up the good work

[@ГеоргиГеоргиев-с3г]

E) all of the above+1, depending on when you stop going deeper, a) instant- if rigid and using classical mechanics, b) if rigid, but with general relativity, c) if rigid, but without heat effects, d) if a mesh, but without heat effects, e) if mesh and you count heat loss, may never measurably reach, aka infinity time. f) b because electricity goes the speed of light and moving metal rod produces current and vice cersa.

[@ГеоргиГеоргиев-с3г]

I was wrong for the short version(also guessed point c (not the speed C), but changed my mind last second) . But at higher lengths, most of the wave will be perpendicular to the rest of the wave, see water wave in a channel, there will be drag off of the edges, even light(if not perfectly parallel) will defuse down to nothing, which is one of the reasons stars shine so dim.

[@hooner2009]

Just ran across your channel... You do an amazing job of explaining/teaching physics with relatable models and analogies. Like and subscribed. My favorite part of this video is the FIRST Robotics clock hanging on the wall. Ive been a FIRST mentor and coach for 10 years now.

[@Born.Slippy1]

Omg. I’ve had this question bouncing around in my head for YEARS and had simply just never bothered to find an answer for myself. This is fantastic!!

[@quiver3160]

This question always plagued me and most of my science teachers weren't able to give adequate answers growing up. Thank you for putting this to bed by giving it the answer it really needed, which was more questions and complexities that encompass more of reality. I am extremely satisfied and you just got a subscriber

[@EyesforSkies]

Cool video! Idk if you've already covered the topic, but a cool follow up might investigate when these models breakdown (e.g. material under Rankine-Hugoniot conditions - plus shockwaves are always cool!)

[@MrLembnau]

Great video. This got me thinking that the speed of sound should be faster in harder materials. and turns out it is. at least when i checked for diamond.(12000m/s) would be interesting to take a bar of carbon steel (arround 0.8% carbon would be ideal) and test the delay in an annealed state and then test it again fully hardened.

[@kylesebring]

Ive had this question since I was about 10 years old, pretty much since I first found out about the speed of light, and the intro captured that perfectly.