Are solid objects really “solid”?

If you think about idealized physics scenarios, "frictionless vacuum" or "ignore air resistance" may come to mind, but another even more ubiquitous mechanical approximation is the so-called "rigid body approximation" where solid objects are said to be perfect geometric shapes that don't deform at all when force is applied. For a LOT of classical mechanics and mechanical engineering, it's a fantastic approximation, but like all approximations, eventually it breaks down. Today I'm demonstrating a failure of the rigid body approximation by asking "When you apply a force to one edge of an object and it starts moving, does the rest of the object actually lag behind? and if so, by how much?
Hope you enjoy the experiment!
Music in this video:
I Dunno by grapes is licensed under a Creative Commons Attribution license (creativecommons.org/licenses/...)
ccmixter.org/files/grapes/16626

[@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.

[@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)

[@brendan12882]

Rule #1: Everything's a spring

[@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"

[@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

[@GregHassler]

"All models are wrong, but some are useful"

[@user-xf8ot1ds2p]

But some are less wrong

[@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!

[@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,

[@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.

[@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.

[@JackOusley]

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

[@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.

[@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

[@jonathanbailie]

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

[@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.

[@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.

[@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

[@personalsinr]

Impressive! Love hearing the behind the scenes design and testing of the experiment as well! Very cool.

[@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!!

[@thethoughtemporium]

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

[@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.

[@admthrawnuru]

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

[@dawnkeyy]

What an amazing educator you are. Knowledge, along with the personality. As well as the straightforwardness of your presentation. Amazing!

[@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?

[@lechiengrand]

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!

[@zmadscientist]

Nice video! great work and explanations!

[@tyranmcgrath6871]

Bro! I had this tought experiment recently! To find your video is awesome.

[@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.

[@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’.

[@davidandrews2883]

Brilliant experiment. Quite elegant in fact. Thank you. Keep them coming.

[@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!"

[@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]

🤣🤣

[@WalterSamuels]

Great experimental setup, well done.

[@randallrathbun2036]

First truly informative video on youtube. I appreciate the care of the presentor and his humility in approaching these experiments, versus the typical rhetoric usually dumped upon the observer as if all truth was encased and questioning the results was heresy. Thank you.

[@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

[@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.

[@angelarch5352]

WoW1!!! that was mind blowing but also made perfect sense at the end haha! Thank you for such a well explained video! :D

[@bruce7sv]

This is one of the coolest video ideas I’ve seen and a pretty nice vid 👍🏻

[@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.

[@FhtagnCthulhu]

I TA'd intro geology back in grad school and a lot of people would have no reaction to hearing about waves travelling through rock, but when you talk about it in terms of displacement people's reaction and intuition were very different!

[@Annihilator_5024]

im new to your channel and the intro is the coolest idea i've seen

[@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.

[@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

[@XIII-TheBlackCat]

Every time I have an obscure physics issue, I find myself on this channel. Like how? I guess I'm subscribing.

[@JonathanUsmar]

Thankyou for showing the accurate experiment first and then showing the process of elimination you used to figure out the correct setup. It's nice (as a viewer) to get to the point quickly rather than dragging it out. But it's also important (for scientific literacy) to communicate how many sources of error you had to eliminate to get the setup right. Bravo 🎉

[@NightmareQueenJune]

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

[@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.

[@chrisrohde7696]

This is the most exciting thing ive seen since the last thing. It also made me forget the last thing. This is so cool and so well done. So much good stuff. Thank you.

[@maxvanN]

This really deserves a very definite like! Good science and enthusiasm

[@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" :)

[@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

[@stevejohnston9606]

That was enthralling, really enjoyed that

[@matthewaragon8588]

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!!

[@yearswriter]

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

[@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?

[@jibranelbazi]

What a great video. Great storytelling and explanations. Very refreshing.

[@yashgupta2036]

Good job brother i really appreciate whatever you do to increase our science and practical knowledge

[@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 :)

[@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.

[@jeffreymartin8812]

Hi! new subscriber here, loved this video and I binged some of your others. great stuff! keep it up, and would love to see what happens to materials cut with a saw on the molecular level haha😅

[@slavsterbater]

I was thinking about so many contraptions to measure the experiment until you showed the oscilloscope and I felt like I was a complete idiot 😂 What a fantastic video 💪

[@viniciusmmd2282]

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

[@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

[@purpledoo]

Amazing work!! Keep going!

[@seanp2k617]

I’ve had this question since I was a kid but never knew the words to use to ask it and didn’t really pursue it. Excellent work. Thanks!

[@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

[@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.

[@VoidloniXaarii]

This was fascinating thinking, thank u so much!

[@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

[@JoshuaFeldman]

A complete tour de force of pedagogy - and meta pedagogy. Seldom has a science demonstration more directly connected with me. Superb work.

[@stevevanscoik398]

Nice job. I was thoroughly engrossed the entire time. I also appreciate your honesty and integrity in trying to find the error in your thinking, and telling us what you found. Can I theorize that the denser the material the fewer free electrons?

[@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

[@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!

[@kenschwarz8057]

Love it, especially the addenda on the messy reality of getting this to work!

[@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.

[@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...

[@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?

[@Jinb-ut7bx]

This Video was highly entertaining and very easy to understand. I am actually really impressed!

[@nosaltadded2530]

Is the delay in the bar or in your measuring equipment? Or is it a combination of both?

[@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!

[@frostbird3431]

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

[@jaspervandenameele4834]

Is it solid though :o

[@AlphaPhoenixChannel]

@@jaspervandenameele4834 ooh gottem

[@ubahfly5409]

This was so great ! Thank you !

[@egoworks5611]

Physics models masterclass. Would have been cool to add also mini animations of the different models you were talking about. Great video

[@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?

[@dingoniner5528]

Just discovered this series. I really enjoy them. You obviously have a passion for this, and that combined with your really clear explanations make these a joy to watch. Thank you!

[@AnthonyFrancisJones]

Well done. This was a standard experiment in the UK many years ago with simple timers. I found it always gave an answer that seemed right but after many years it appeared to me that whatever you did the kit 'happened' to give an answer of the right order of magnitude! All good fun though!

[@609neo]

I think you should have measured both the hammer impact and the force on the other end using the same type of pressure sensors. Also repeat the experiment with the sensors on either end swapped and averaged in order to get a fair observation.

[@cslloyd1]

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

[@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!

[@riverbender9898]

Beautifully-presented! Thank you.

[@ShaharHarshuv]

I love the exlanation and the break down of how you figured it out!

[@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

[@DashCamSamVids]

Reality has a lag time. This blew my mind when I first learned it.

[@Produkt_R]

I'm not bad ad stuff, it is the lag. High ping and such.

[@seanriopel3132]

Even looking at a mirror takes fraction of a second for the light to travel from your face to the mirror and back again. Looking at the stars it's looking back in time.

[@xBINARYGODx]

lol no, it does not - or rather, that is a misleading way to say it.

[@Lrofmaulol]

@@xBINARYGODx is it though? The propagation of information, on which causality builds upon, has a finite speed. Therefore: reality has lag. Our 'perceptive' reality anyways We'll see how well this statement ages with advances in our understanding of quantum phenomena, entangled particles are already theoretically able to transmit information across lightyears of distance 'instantaneously'

[@allorfh2495]

if you think about it, the lag you experience in games is kinda because the irl world is lagging.

[@tickytickytango5634]

"I can't even come close to deforming it like this" *immediately deforms it*

[@kaComposer]

Thank you for this video! I've been looking for an explanation. I've been imagining objects colliding in a void to try and visualize this.

[@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

[@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.)