Watch gravity pull two metal balls together

[@SteveMould]

EDIT: I want to address the comments that say gravity isn't a force, it's the curvature of space time. There's an interesting philosophical point here. The way I think of it is this (I'm not the first to say this but I can't remember who was): physics just gives us models for how the univers works. None of them are "true" but some of them are useful. Newton's model of gravity that describes it as a force is really useful. It doesn't work in certain circumstances. Einstein's model, that describes gravity not as a force, works in more circumstances but is more cumbersome. You pick the mode that best suits what you're doing. In this vide Newton's model is the most appropriate in my opinion. So talking about gravity as a force is perfectly reasonable. Like, imagine being in a physics lab with some springs and pulley or whatever, and you're trying to balance the forces, and every time you mention the force of gravity, someone pipes us and says "I think you'll find gravity isn't a force". That person is unhelpful. Other commenters are saying gravity isn't a force for another reason, which I believe is related to a non spherical model of the earth that they believe in. We can safely ignore those comments. Here's a fun fact: if you scaled down the earth and moon system until the earth was the size of a bowling ball (keeping the density the same), it would still take the moon 27 days to orbit the earth. This is true in general. Like if you scaled down the ISS as well, that would take the same 90 minutes to orbit as it does now. It's true at any scale, not just bowling ball scale! The sponsor is Brilliant: Visit www.brilliant.org/stevemould for 30 days free access. The first 200 people will get 20% off an annual premium subscription.

[@commanderofthewind]

Great video once again Steve. You were mentioned in a question in my school's yearly Christmas quiz, seeing at you went there.

[@zverh]

How do we know if the masses move towards each other due to gravity or the motion results from the rotation of the earth?

[@ImieNazwiskoOK]

@@piranhaofserengheti4878 Similar reason why a magnet sticks to the fridge even though it's still pulled down

[@ThisSteveGuy]

Would using flat objects instead of spheres make a difference?

[@DoobooDomo]

@@ThisSteveGuy I was wondering the same thing since flatter objects should allow for the center of masses to be closer (which I think would be more significant than the change in moment of inertia)

[@Rubrickety]

I’m glad you showed your homemade experiment even though it didn’t work. That took balls.

[@Jo24Park]

of 14kg steel

[@dan-nutu]

I wish I had those! 😃

[@Lucius_Chiaraviglio]

Normally I don't like expressions that equate courage with "balls", but in this case it's technically correct, which is the best kind of correct, and thereby too good to pass up.

[@faq_is_love]

r/techicallythetruth

[@ohthatsclever]

Giant 14kg iron balls

[@Impatient_Ape]

Great job, Steve! 10% error is typical for what physics majors get when they do this lab experiment using the 2nd apparatus you used.

[@tormodhag6824]

What about using a bunch of photoresistors to measure the fluctuations in the laser? It could keep measuring for longer, and would probably give a better value?

[@GerinoMorn]

@@tormodhag6824 yup, and then you find out more precise G :D

[@wallyhall]

I was thinking similarly - with a measuring rule on the whiteboard and a time-lapse overnight 😀

[@Impatient_Ape]

@@tormodhag6824 Real undergrad physics lab experiments are always messy, and you need a human to see what should and shouldn't be counted as "data". The experiment Steve shows with the physics lab apparatus is one we use to educate physics students in experimental techniques -- especially the use of mirror and laser to measure angular changes; it's not to try and improve the known value of "G".

[@bholdr----0]

@@tormodhag6824 I wonder if a jewlled bearing (like those in high-end mechanical watches, which are as close to frictionless as one can easily get) would make the results more easily observed? (Though, that would complicate the measurement of G... Increasing the length of the wire suspending the moving weight would also aid in taking an accurate measurement, eh?) Once in college, a pal and I built a foucault's pendulum, just to see it work, which it did! (I mean, of course it did. Cool to see, though.) We used monofilament fishing line to hang the (45lb) weight, I can't think of any line as light and strong as that... What is used in these setups? Did he mention that? Cheers!

[@jasonpatterson8091]

The Cavendish experiment and Millikan's oil drop experiment were the two historical experiments that really struck me when I was studying physics. Being able to see gravity directly, or being able to see the influence of a single electron's charge - it's just mind blowing. I love Von Jolly's version of the thing as well.

[@Michaelonyoutub]

When I was doing physics in university I did both of those experiments and I completely agree. Millikan's oil drop is especially interesting as measuring such a single charge seems absolutely impossible initially, way harder than just showing the effects of gravity between two objects in a room.

[@manpreet9766]

Me too. I consider it to be one of most important experiment in science history. The another one is Michalson Morley Morley experiment paving way for theory of relativity

[@replica1052]

(where gravity is shielding from cosmic radiation gravity can never exeed the speed of light )

[@slightanxiety]

I got to do Millikan's oil drop experiment in college, and got pretty decent results (I think we were within 50% of the actual value, and we had distinct peaks for 1e and 2e charges). There's something really magical about being able to measure such a tiny quantity to any degree of precision.

[@impaler331]

I wish I knew about this experiment when I was a teenage flat earth tard. Would have saved me a year or 2 😅

[@thegamesforreal1673]

In my first year at university physics, we did the exact same Cavendish experiment you did to measure G, laser pointer and all. By sheer statistical wonder, despite the extreme finickyness of the experiment, me and my lab partner somehow got the value nigh-bang-on at 6.68*10^-11. The professor simply didn't believe we were that close until he looked at our measurements directly. He said it was the first time he'd seen that anyone measured it to within 0.02*10^-11 accuracy. But then when we calculated the error margin on our measurements, it turned out we had a margin of error of nearly 10x that...

[@TomJakobW]

xD ah, I remember those. good times, good times. I had one graph in second semester that I hand drew (out of time constraints; deadline was closing in) on a single page of my report & I still remember the assistant actually bursting out laughing when she turned the page; hard to describe, it was absolutely comical. To be fair, it *did* look like a 4 year old drew it with fingerpaint, sooo.. 🤷‍♂️🫠

[@MrCuddlyable]

Your professor should throw out your result that you quote as a number. G is not just a number, it has units that need to be quoted.

[@thegamesforreal1673]

@@MrCuddlyable Youre saying this under a video about the cavendish experiment... We all know which G we're talking about, go be pedantic somewhere else.

[@lht001300000]

It is not about the number but the uncertainty. Imagine you are in a world not knowing G better than ~1E-10, the main challenge to propose G~6.68(20)E-11 (or whatever 6.xx(20)E-11 that happened to come out of your experiment), is to convince all your not-so-friendly peers that you did nothing wrong that would result in a 10x increase in uncertainty. This is the process of peer-review. It is definitely challenging to measure small anomalies mixed into bunch of much stronger effects. This is pretty much a branch of scientific research even nowadays, and professionals slipped from time to time, e.g. faster-than-light particles discovery in the late 2010s, only turned out to be a faulty data link or so; or the famous LK-99 in 2020s. The takeaway, if you happen to discover a new anomaly, be prepared to face someone who is going to inspecting your apparatus atom by atom.

[@Piineapple.]

Ah, yes, chance

[@reinerwilhelms-tricarico344]

We did this experiment in a physics lab many years ago using a small mirror attached to the center of the horizontal bar so we could use a light beam to more accurately observe the deflection, noting the angle every minute or so to make a graph. It took several hours. When it was finished we found it was a damped oscillation as expected, but there was a moment when the amplitude increased instead of continually decreasing. We later found out that a small earthquake had occurred during the experiment.

[@FireFusionYT_0]

That has got to be a lucky catch. Amazing!

[@pansepot1490]

Earthquake detector. 😊

[@ezdispenser]

wow, that's really cool

[@henriquedolzane]

That's awesome!

[@spikeman5103]

Well, during the 80th in German HighSchools this has been a standard experiment, even with the mirror and a scale on the wall (but normal light).

[@KnowArt]

I vote for a sister series to Matt's calculating pi by hand series in which you calculate g in more and more elaborate ways

[@Becky_Cooling]

That would be cool!

[@ploploprob]

Or e!

[@Hinotori_joj]

im not sure theres that many ways to calculate G, but i would also love to see steve calculate physical constants in various ways alongside Matt's Pi.

[@Impatient_Ape]

IMO, the best and *cheapest* way -- hands down -- to estimate little "g", is just a dense metal pendulum bob on a very long cord timed for multiple periods over a very long time at a small displacement angle. You can actually use this technique measure the difference in "g" at sufficiently different altitudes (like say, between Denver and Philadelphia).

[@idjles]

g is easy to calculate, G is much more interesting

[@FelipeKana1]

Remember folks, an experiment with a failed result is still an successful experiment! It's very important in science to not hide the mistakes, but to document them throughly and try to understand the failure. Great video

[@doofismannfred4778]

This is a very important takeaway. Documenting processes shortcuts the thinking process for others who may want to offer suggestions, seeing what was already tried.

[@jemfalor]

sounds like anybody could do it

[@seppdipode2203]

​@@jemfalorand anybody _should_ do it if they can, if they want to discover it for themselves. That is the whole point. The only requirement is that you note down and publish the parameters you used to the best of your ability. Regardless of success or failure, everyone must be able to indulge in science.

[@melonenlord2723]

But it's only really useful if you know what went wrong.

[@CalebDiT]

In many cases, however, it may mean your experiment was not well designed, perhaps due to a misconception or whatever. There's no telling how many discoveries have not been made because the experiment, as designed, was never going to answer the question. Similarly, there are false discoveries that have been made because the person didn't understand the influence of his design. I'm not saying either of those is the case in this video, but being artful and imaginative in ways that are helpful to discovery are no small part of the design of the experiment. Science can't be done by just anybody. _"The formulation of a problem is often more essential than its solution, which may be merely a matter of mathematical or experimental skill. To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science."_ -- Einstein and Infeld (qtd from _Collective Electrodynamics_ by Carver Mead)

[@frantisekvrana3902]

6:40 The cause can't be charge. Both objects are metallic, so if it was charge, it would just equallize on impact. But the weights did not rebound.

[@larrywiniarski1746]

Great point, but I should note that probably only 1 side would make contact and the other is just artistically close, so I don't think charge is completely ruled out and I don't think I would bet my life on 2 pieces of weathered oxidized lead barely touching each other making a great contact either.

[@roy28372]

I did this experiment during my undergrad at IUP. We found that we could get extremely accurate results if we set the device (which took results electronically instead of via laser) to work overnight. Even in the basement of a concrete and brick building, the footsteps of people inside threw off the results. We took results overnight on two nights. About 140k datapoints if I remember correctly. We ended up off by 1.4%. The next group used the procedures we had come up with and were off by about 1% as well. Basically, it was a good lesson in looking into sources of error. (In that course, we had to design our own labs with given equipment to reproduce some of the most famous discoveries in classical physics.)

[@MikkoRantalainen]

I think you will always end up with some error because the masses in the walls of the building will affect your local gravity, too.

[@DUKE_of_RAMBLE]

Now, while I know first hand that buildings, sizable ones, move with a person's footsteps... But at the same time, it'd be pretty wild if it were OUR masses just being in proximity, that caused those error rates!

[@UCreations]

I did it too (back in 1997 at the University of Utrecht) in a basement. The setup was placed on 5 concrete tiles on a crate of tennis balls on some foam rubber mats. I could see exactly when people came in the building every morning. The experiment took 3 days. I came also within a few percent of the real value of G.

[@chuvzzz]

I don't think this is a good video, it was unconvincing. This measurement was supposed to be based on this great achievement, requiring great care and precision. There's people walking around, touching things, potentially introducing charge, who knows what. Sure the measurement was "relatively" close, but is that actually significant? Doubt. If we are just supposed to take Steve's word for it, sure, but then what is even the point of a 12 minute long demonstration video? If it is potentially misleading, better not to do it at all. This is G we are talking about.

[@doofismannfred4778]

@@chuvzzz What was the video supposed to convince you of? He got the same kind of results that secondary education students get on their own. I had a similar experience with a similar kit. Everything in this video seems alright.

[@robadkerson]

Mould's Law: a stiffer spring boyoyoings faster

[@heatshield]

Pretty sure it sproings quicker too.

[@R_Euphrates]

Man you beat me by an hour lol. Well done

[@unibiker8087]

Thats what my wife says

[@jwigeland]

Literally made my day! 😂

[@guerra_dos_bichos]

​@@heatshieldthis is a place of science , stop this mumbo jambo

[@ssskillzzz3513]

2:51 "...Boi-oi-oings more quickly." 🤣🤣

[@dracomaster4]

He said it so fluidly and nonchalantly I took three full seconds before I realized what he said 😂

[@davydovua]

That is a correct scientific term for spring behavior, boioioinking

[@garryghibli5993]

Shoutouts to Simpleflips

[@smitajky]

I did this same experiment in a classroom with my year 12 class. I used piano wire and 50 kg of suspended masses. It had an oscillation frequency of over an hour from which we could know the stiffness of the spring. By introducing the stationary masses we found the shifting of the centre of the oscillation. That gave us G to one significant figure. It was the only time that I was actually able to demonstrate Cavendish experiment. Taking many hours to achieve a result.

[@11moonshot]

Oh yeah... this sort of experimenting is tiiiiiiime - consuming... If you are married ... it can bec ome an issue;-)) I did nearly the same...here in Dresden

[@Bob_Adkins]

Did you reverse the stationary masses a few times and note how closely they repeated? If they repeated very consistently, it would make your experiment very convincing!

[@pyropulseIXXI]

Weird. They don’t even do this experiment in the best colleges of undergraduate physics because it never works. I would know, since I majored in physics at UC Berkeley. We have multiple Nobel Laureate professors, and still this experiment never works, so it is skipped at an undergraduate level. Also, the ‘oscillation frequency’ is so long that you are basically choosing what value to use, thus nearly all experiments are choosing the value that gives agreement with the accepted value of G. The turn around time at the top of the wave is so slow that the error bound in where it actually turns around, and thus what your oscillation time turns out to be, is so huge as to produce any value you want in a huge range around the ‘accepted value.’

[@vnarayan18]

@@pyropulseIXXI :( Yeah it is weird to me too but that's just how it is in Asia

[@carykh]

That idea of using laser reflections to get a finer measurement of rotation is so clever! It reminds of, when I was in a car on a sunny day playing with a reflective Rubik’s Cube, even the tiniest turn of a layer of the cube (like under 1 degree) would send the reflections of the 9 squares of a side way out of alignment!

[@bencressman6110]

Cary!! I miss you! Are you still posting videos? I will now go and find out

[@CCABPSacsach]

Hey look, it’s Cary Knowledge Holder himself! He’s the guy who made BFDI! And now, he’s revived EWOW! I didn’t expect to see him on THIS vid Ok but that Rubik’s cube story is actually pretty fascinating. Light works in such strange ways…

[@terigonUSAS12]

i cant believe they made a human named after the dwarf planet

[@douggale5962]

Unless they aimed the laser perfectly, it would be applying force to the mirror. It would be a terrible light sail.

[@6F6G]

Photon pressure from the laser could affect the reading.

[@anmolagrawal5358]

2:51 That boi-oi-oing was so well delivered, I felt the springiness within

[@RielMyricyne]

Concerning Mr Lund's experiment : I looked up for common impurities in crude, unrefined lead. I found it typically contains measurable amounts of 6-7 other metals, including up to 1% of nickel. Nickel is ferromagnetic. Could there be some magnetic interaction from that?

[@thejuggler42]

My thoughts exactly. Testing the magnetic charge of the weights to make sure it's effectively zero before doing the experiment would have been wise.

[@sslavi]

On top of that, the electrostatic charge (hypothesized in the video) can be excluded, because it would drop to zero in the instant the two masses in Lund's experiment get in contact and equalize their electrostatic potential. No electrostatic force would be felt by the two spheres after that moment, countrary to the body attraction which is shown in the Lund's video even after the first contact.

[@hedoverheels]

Looked to me like like the lead weights are attached with heavy-gauge mild steel wire, a much more likely source of ferromagnetic material.

[@hedoverheels]

Strike that. He said the *stationary* mass was lead, so the wire wont make any difference.

[@MusicBent]

I did this experiment for my 8th grade science fair and had the same issue with sensitivity. I replaced the wire with fishing string, used 2 pound lead weighs on my bar, and 15 pound lead weights on the floor. I used a small paddle hanging from the bar into a dish of water to dampen the noise from air currents. My setup meant I couldn’t use the torsional rigidity of the string, which was now almost zero, but using a time lapse I could measure the position of the bar as the bar swung from ~80 degrees off, to the lead weights touching. Position -> velocity -> acceleration. I think I was quite off, but within 2 orders of magnitude. Basically just confirming gravity’s pull was measurable, but very weak. That was pushing my limit of understanding of physics at the age. I remember being really awed at being able to see gravity behave in a way I’d never seen before

[@HeatherHolt]

Wow, very impressive for 8th grade! Very cool.

[@exel001]

Finally, someone on KZbin has calculated the proper deflection angle! Props to the author. :) Before that, I watched a bunch of videos about someone quickly cobbling together a setup to observe gravity in their room without even realizing how tiny the deviation should be. That includes the video the author showed as example.

[@joeomundson]

Yeah, that other video immediately seemed glaringly wrong. Just intuitively, if that reaction really was due to gravity then you'd expect to almost feel pulled by big rocks and buildings when you walk by.

[@-ZH]

@@joeomundson Its not that glaring since the video was playing at 30x speed

[@bigsiege7684]

If Steve also dropped rocks from a height, found g, and then calculated the mass of the earth, it would be doubly cool.

[@joeomundson]

@@-ZH I know it was sped up but even still the magnitude seemed like a lot

[@declanwk1]

@@joeomundson I agree, the deflection in the Mr Lund video was far too large for it to be due to gravity, and it does not matter what speed the video was played at

[@Impatient_Ape]

The surface of that PVC tube separator is very easy to charge and notoriously difficult to discharge -- even friction with dry air or skin can leave a residual charge on it. Since it's highly unlikely that such charge is uniformly distributed over the plastic, then the PVC acts a bit like an electric dipole, so it's an effect you have to try and eliminate. As far as the torsion in the hanging wire goes -- the longer the wire, the better.

[@carlosgaspar8447]

wouldn't the charges neutralize once the two masses made contact?

[@Suleiman212]

But the Virgin (presumably Mary) didn't call her son (Jesus) Immanuel. So who is that prophecy referring to? Better go back and read the context in Isaiah to find out.​@Repent-and-believe-in-Jesus1

[@Impatient_Ape]

@@carlosgaspar8447 If one or both of the metal balls initially have some charge on them, it is likely to be unequal. When they make contact, some charge will shift from one to the other resulting in a *net* charge which will be shared by both balls. Then both metal balls will end up with the same polarity charge, causing repulsion and not attraction. However, the larger metal balls don't need to be charged to be attracted to the charged PVC or copper balls. This sort of attraction occurs because of "induced charge", where the external metal ball is overall neutral, but it has one charge polarity at one end and the other charge polarity at the other end. The presence of the external charge causes this separation of charges in the metal.

[@fakestory1753]

​@@carlosgaspar8447he said pvc pipe not the mass

[@samstarlight160]

​@Repent-and-believe-in-Jesus1Nobody asked xD please dont spam random videos

[@Afdch]

"Watch gravy pull two meatballs together". I'm being totally honest, that was what I read and now I am a bit dissappointed it wasn't that. Dissappointed and hungry, apparently.

[@orthochronicity6428]

We had this experiment as a possible advanced lab during undergraduate. Most people purposefully avoided it because it was notoriously finicky. There, it was pretty big torsional pendulum placed inside a Faraday Cage. Improper grounding will absolutely mess up the experiment. A friend of mine did the experiment and discovered a grounding fault that was the source of all her error; no one knew how long the fault was present. There was also a case when I was taking the class, that one of the members of the group doing the Cavendish experiment came into the common room very animated a cursing. We immediately asked him what was wrong, and apparently a friend in the class though it would be funny to lightly slap the faraday cage. That one impulse set the pendulum oscillating so much it was going to take most of the remaining lab period to settle down (we had three weeks to do each of these experiments); I'm pretty sure the friend got in trouble with our professor, both specifically for doing that to them, and more generally for incredibly inappropriate laboratory behavior and, effectively, data tampering.

[@hellomate639]

I drew a giant eyeball on the board while I did it.... lol. Maybe someone who went to my university will know what school it was if they see this comment.

[@Harkmagic]

I've done this experiment before with something very much like what you used at the end. This experiment is unbelievably sensitive to vibrations. If you plot the position of the laser over time you can see people walking across the room in the plot. That's why you should do it when nobody else is around and have the laser pointing at a surface as far away as you can get it so that the person taking the measurements doesn't disrupt the experiment moving around.

[@tatatatmax]

If you decrease the mass of the copper balls, the period of oscillation will get shorter; and by the equation, the measured angle will be less. You can counter that using a less stiff wire, but now you'd have a super light system that is more sensitive to things like air currents. The best experiment really is to use heavy masses that are as close together as possible.

[@andrewharrison8436]

Given that the important distance is between the centers of the pairs of masses then would disks work better? I think they would but the equation wouldn't be as simple.

[@kiralycsavo0]

Heavy and dense masses, e.g. tungsten balls are better than iron.

[@CorePathway]

Or you could use yo mama for the stationary mass. She brings a lot of mass to the party.

[@beefchicken]

Wouldn’t the best way to do the experiment be to do it in a vacuum?

[@victorfinberg8595]

the effect of air currents is removed by placing the central setup in a box

[@DrSimonFoster]

I helped set this experiment up and I can tell you that Steve has the patience of a saint! He very much downplays just how tricky and finickity this experiment was to set up! I had to leave as I thought I was losing my mind and it reminded me why I am not an experimentalist! Frankly, I am blown away with how well this came out!

[@SkemeKOS]

And yet he still didn't wait for it to fully stop, completely invalidating this silly 'experiment'.

[@mrosskne]

@@SkemeKOS Nope.

[@estrheagen4160]

Getting not just the order of magnitude but also one significant figure in the lab is bloody amazing, top job

[@fatsquirrel75]

Sure. But the scientists get the credit there. Steve just turned up and used their kit.

[@andrewfrance1047]

We measured it this way with the torsion fibre and optical pointer when I was at school nearly 50 years ago. Our apparatus was less refined and it took hours to settle.

[@haydenw7981]

God physicists are funny as hell. "congrats on getting the correct order of magnitude."

[@ArsenicDrone]

A couple thoughts about what could cause the Lund result, in decreasing order of how likely I think they are: 1. Disrupted the air currents in the room, creating areas of lower pressure between the lead bricks and the hanging blocks, which would compel them to move together. 2. Affected the equilibrium of the hanging blocks by the force of setting down the lead bricks (some motion or vibration in the floor affecting his mounting structure) 3. He says he got them from a cyclotron. Perhaps being blasted with protons had some effect on his lead bricks.

[@mozartk465]

I wonder if there could be some beta decay generating electrons.

[@kwindafidler7728]

thought he would talk about your first point, greatly illustrated by 2 ships getting too lcose on open sea but does that mean the lab pendulum was evacuated?

[@bluesbest1]

@@kwindafidler7728 The lab pendulum isn't suspended in a vacuum, it's just separated by glass panes. Remember, it's not disrupted by air itself, just the movement of it.

[@ceejay0137]

If the lead blocks were slightly warmer, they would set up convection currents that would pull air towards the blocks and move the suspended masses in the same direction.

[@kwindafidler7728]

@@bluesbest1 oh but of course, thanks for pointing out

[@prian42]

Brings back memories of being a physics student and measuring G at Imperial College. In our lab experiment we had equipment that moved and tracked the laser beam resulting in the positions being recorded, thus making the final analysis easier 😀

[@milkwater1204]

No way, I'm an ICL Physics student, too!

[@weejockrock]

This was one of my lab projects as a physics undergraduate at Imperial College! The apparatus shown here is much nicer than the version I used 20 years ago. Thank you for another interesting video, very nostalgic for me.

[@kriscollinstunes]

“the boi-oi-oing” 😂😂😂 Well said! Efficiently and effectively conveyed what you were talking about. Honestly brilliant. 👏👏👏

[@2eanimation]

It should be adopted as a scientific term, like "spaghettification".

[@footballkickerswag]

Came straight to the comments when he said that 😭

[@maxgood42]

Now I know what that is called.

[@kenfryer2090]

Amateurish and childish. Obviously this channel is meant for small Children

[@kriscollinstunes]

@@kenfryer2090 troll

[@rsaunders57]

The availability of optical fibre makes that a much better material than wire. I did this experiment for the local High School physics class as a guest experiment. The laser pointer was pointed to a ruler taped to the wall. Then with a time-lapse video recording, the students could calculate big G. This was so cool now that everybody has excellent access to time-lapse video.

[@broccolihighkicks708]

He is so dedicated, his hair cut was oscillating the entire video.

[@vitorsales2492]

lol, not everyone noticed that

[@redmed10]

Ha ha nice one.

[@DUDE607-ft7hq]

Took me so long to find a comment saying this, as I thought I was just being crazy

[@Sednas]

I noticed it and i was so confused

[@plogger74]

👍 I thought I was the only one who was wondering...

[@reginaldx]

In undergrad I had a little project to modify the Cavendish experiment to measure G using driven oscillations. The larger M was oscillated slightly farther from the axis than the smaller m, so that they wouldn't collide; to a first-order approximation the torsion balance would act like a damped driven harmonic oscillator. At the resonance frequency, the amplitude of oscillation would be much larger than a simple stationary attraction. It was a crude setup but I got a decent value for G (with large error bars, lol). Most importantly, it worked as a proof of concept. It's an interesting experimental challenge -- introducing oscillations means the oscillators can sync through all sorts of things other than gravity (the ground, the air, etc.).

[@kierana.carroll672]

Steve, as always, very enjoyable. This one particularly so for me, as I spent 14 years as part of a team working on developing an instrument that was a several-generations-later descendant of Cavendish's torsional pendulum --- a gravity gradiometer, which measures the spatial gradient of the gravitational force field, and is used in geophysical exploration. The inventor of the first gravity gradiometer, the Hungarian physicist Loránd Eötvös, based his design on Cavendish's experiment; with the aid of what is effectively tensor math (although he did his derivation in scalar closed-form equations), we was able to show that by using a modified Cavendish torsional pendulum, making measurements with the base oriented sequentially in several different directions (over the course of several hours, to let the oscillations damp out), he could directly measure several of the components of the gravity gradient tensor, as well as compensating for the instrument's bias term. And with that information, for measurements taken at multiple locations throughout a region, inferences could be made about the subsurface density distribution --- which circa 1900 turned this into a powerful tool for discovering oil & gas deposits. Brilliant work! Our particular instrument (at a company that's now gone, called Gedex) was a variant of his, customized to be able to operate aboard a small aircraft flying low and slow over the ground (!) --- we managed to get it working, and demonstrating far, far greater sensitivity than Eötvös did in his ground-based measurements, despite being aboard an aircraft bouncing around through the sky...and then the money ran out 😞... Anyway, I wonder if there's anything you could do with the concept of a gravity gradiometer, and/or gravity gradients...

[@elmoking95]

Incredible story and work. Thank you for your contribution to science and humanity. I hope he sees your comment and gets back to you!

[@ianglenn2821]

is synthetic aperture radar on satellites used for this now?

[@kierana.carroll672]

Synthetic aperture radar (SAR) is indeed used for remote sensing of Earth from orbit. However, it works differently from a gravity instrument, and measures different things, and so tells you different things. A gravity-measuring instrument detects changes in the gravitational field of the Earth, and it does that passively, just by measuring the tiny changes of position of a test-mass inside the instrument itself (as in Steve's video). It tells you something about how much variation there is in the density of the rocks inside the Earth, which in turn can help to understand the geological structures underground --- the types of rock (as different types of rock have differing densities), and their structure (layering, presence of fault-lines, etc.). Whereas SAR is an active method, that involves beaming a powerful radar signal towards the Earth, then measuring its reflection (as in any radar system), followed by very complicated post-processing of that signal in order to create something that looks like a picture of the Earth's surface (not its interior). (Canada's Radarsat was one of the early SAR missions, and I actually did a bit of work on that too.)

[@Kycilak]

This is the first time I see Eötvös' name in the wild. I didn't know he did such a thing, I know him from his contributions to physical chemistry of surfaces. The scientists back then really did stick their finger in every field imaginable.

[@lunam7249]

the money didnt run out, ....the military took it and said "thank you", its prolly been improved and part of a top secret program

[@pensivist]

Thank you, Steve. The Cavendish Experiment from MrLund has always annoyed me because it is very clear that the movement is too big for what one would expect of the actual force of gravity. So many comments on that video think that is real. In fact, even the most subtle air current in your room could make more impact than the force of gravity. I was ecstatic to see how you would deal with the experiment, as it is a very hard to replicate. Watching you use professional equipment in a lab didn't disappoint!

[@andrewm9425]

Also he never did the obvious next step which would be to move the bricks to the other side and see if the thing turns the other way. And he didn’t film for nearly long enough.

[@Scrogan]

Ah, the perturbation of air currents as a result of the stationary bricks could well have been the cause of the deviation.

[@Dexter_84]

It's not really hard to replicate. We did it at high school in a 90 minute lesson. Came out fairly close to the real gravitational constant. Standard experiment at my school.

[@pensivist]

@@Dexter_84 In the video Steve mentions the awful amount of time that the torsion balance takes to settle in. I'm skeptical this experiment can be done properly in 90 minutes.

[@StWhitcomb]

I do suspect the air currents, and eddy vertices behind the rectangular led bricks help to pull the weights in, while your spherical weights allow for smooth airflow and prevent the same. Well done. Commercial (school) rooms will tend to have a gentle overall flow of air mass across the space, engineered into the HVAC system to be imperceptible but still a factor. Custom residential sutio space for fewer occupants is may not have the same.

[@JDNboy12]

i'm glad the guy who made the original video was receptive to feedback and decided to keep the video up. i was scared for a minute that you were going to say they made the video in bad faith

[@sebastianpostigo4025]

Es que los terraplanistas y conspiranoicos niegan toda evidencia Estoy discutiendo con una desquiciado que dice que el experimento de Cavendish NO PUEDE SER REPLICADO y que todos los experimentos están mal ya que no se han hecho en situación de vacío absoluto

[@redwood9120]

The experiment brought me here…and the haircut at time stamp 6:15 that happened in under 7 seconds blew me away. Great video and smooth editing for sure!

[@quantumbacon]

"static electric shock"

[@gtwgtwgtw]

HA HA!! I was sure I was the only one who found that distracting...I had to go back and look to see if I was just having a mini-stroke or if it indeed was different! :)

[@robertgill5865]

And he grew some serious facial hair in those same 7 seconds too!

[@hypotheticalneutronstar]

when your mom wants you to get a haircut but you're recording a youtube video:

[@jacksonbruns9429]

2:49 petition to make boi-oie-oing the official scientific name for a spring springing

[@jacksonbruns9429]

having a conniption over if it’s oi or oie someone let me know 😂

[@vigilantcosmicpenguin8721]

who do we need to talk to to get this to happen like the SI or something

[@jacksonbruns9429]

@@vigilantcosmicpenguin8721 prolly faucci 🫠🤣

[@nothingissimplewithlloyd]

Did anyone else notice that he got a haircut between shots at 6:25?

[@RehanAshraf-q8u]

😊

[@ikariameriks]

Even before that. He jumped before and after

[@IngmarSweep]

Thank you for not disturbing your nice video's with background music, like so many others do.

[@azzteke]

videos, not video's.

[@BillSevere]

This video is special to me. My 8th grade science teacher, who was awesome, made a contraption that had a laser pointer on one end and a copper sphere on the other, with 100ft of "lever" constructed between them in a sort of zigzag fashion. He took another copper sphere and when he slowly brought it really close to the other the laser would move on the wall because of gravity. I don't know how accurate it was with twenty 8th graders around, but that lesson has stuck with me since.

[@PopeLando]

This is how Henry Cavendish calculated the constant G. Isaac Asimov told this story and at the same time dealt with something that always bugged him about the terminology of what Cavendish did. So he titled his article, "The Man Who Massed The Earth."

[@jasonpatterson8091]

That's how newspapers reported on his results at the time as well. Nobody outside of science cared what G was, but the gee whiz value of weighing the Earth?

[@andrewdonatelli6953]

Best thing I heard all day. "A stiffer spring boioioings more quickly."

[@omp199]

@@jasonpatterson8091 No, PopeLando is saying that Asimov was reacting _against_ how people were reporting what Cavendish did. They said that he was _weighing_ the Earth, which was inaccurate, because it was not the Earth's weight being measured but rather its _mass._ So as Asimov reportedly wrote, it should have been referred to as "massing" the Earth. Weirdly, I have only managed to find one other on-line comment about Asimov's article, and that comment says that Asimov titled it "The Man Who Weighed The Earth". The commenter wrote, "In it, Asimov bemoaned the terminology, saying that it actually should be 'The Man Who Massed The Earth', but that popular usage (including his own colloquial descriptions) required the inaccurate title."

[@PopeLando]

​@@omp199I'm only going by the (UK) book version, which I'm sure said, "Massed."

[@omp199]

@@PopeLando Do you remember which book it was in? I do have some collections of Asimov's essays, so it's _possible_ that I have it somewhere.

[@uxkwn4894]

Steve explained gravity so hard, his hair went back inside his head. truly a big brain moment.

[@ianloh2647]

Ikr. I was so into it but totally got thrown off by the haircut 😑

[@johnnyasia7903]

I had to rewind about half way through because I was sure something had changed. The hair grew straight back again shortly afterwards too. Glad I'm not the only one that got thrown by it.

[@matthewperkins288]

I tried this in my physics classroom at the high school but the hvac and the fact that my string was wound held me back.

[@rmeja]

There is also a problem if only one of the balls is ferromagnetic. Any net magnetization of this ball will lead to forces with most materials even if they are non-ferromagnetic (i.e. paramagnetic/diamagnetic).

[@mesaplayer9636]

True but I assume it's hard to get the pairs of balls to have the same electric force so it is probably better to just not have them be able to attract like that.

[@BluesJayPrince]

i was curious about this too, but I'm not exactly well educated on the details of the two lesser known magnetisms. From what I have seen even relatively strong magnets only induce a very small force on paramagnetic/diamagnetic materials. So I'm guessing with a ferrous metal with no noticeable magnetic field, the force is small enough to be ignored? Hoping someone more confident can confirm/deny.

[@aluisious]

Everything in the room is interacting with the earth's magnetic field, which is much stronger than the gravity between a couple of stupid metal spheres. Really think about it for a second. Are you measuring what these two dinky masses are doing to each other, or are you measuring their interaction with the seething sphere of iron thousands of miles across rolling around just under them? @@BluesJayPrince

[@Qkano]

I'd replace the iron balls with lead ones (or gold ones if it was a government project).

[@zeroone8800]

Lead is the cheapest metal on a per mass basis and is denser than iron increasing the effect two ways: decreasing the distance between the masses and increasing the large masses.

[@Wintergatan]

So cool, thanks for the top quality every time!

[@WordHou]

Oh, hey, it's the marble guy.

[@amosbackstrom5366]

This is a guy who knows his balls

[@lvn5609]

But the question is, can marble machine 3 play tighter music if it takes into account gravitational forces?

[@flanger001]

Thank you for your beautiful musical videos!

[@TheRealDorran]

@@amosbackstrom5366 🤨Dude, it's marbles

[@stargazer7644]

To avoid the charge problem, just bind all the conductive balls together through the torsion wire so they're at equipotential. Attach the two balls on the pole electrically to the bottom of the torsion wire. Attach the top of the torsion wire to each of the stationary masses. Bond that to ground. This should neutralize the charges.

[@Impatient_Ape]

It's difficult to completely discharge the PVC tube surface in his first setup. I would wrap the PVC tube in alum foil and connect that to everything like you suggest.

[@mikeyforrester6887]

I think if you attach the torsion rod to the masses it will change the torsion. it has to spin freely

[@kiralycsavo0]

Yes, or just touch them together once so that their charge equalizes.

[@foogod4237]

@@mikeyforrester6887 The idea wasn't to connect the rod directly to the stationary masses. The rod is suspended by a (conductive) wire, so you just need to connect the _top mount point_ of the wire electrically to the masses (by running a wire back down from the top of the apparatus), and the suspension wire itself will connect that to the suspended rod/masses. Of course, in this setup you'd also need to replace the cords and tape and such with conductive wire or something instead, so it could conduct all the way through to the weights/bar. And it would probably be best to use a metal rod (maybe a thin aluminum tube or some such) instead of the PVC, just to make sure charges can all move freely through the whole apparatus and can't build up at any one point.

[@Impatient_Ape]

@@kiralycsavo0 You are assuming the charges on the balls are initially opposite sign and equal in magnitude, which would be very rare. If you do what you are suggesting, then both metal balls would end up with the same sign charge made from whatever didn't neutralize, causing repulsion.

[@marcinsocha1500]

"Other commenters are saying gravity isn't a force for another reason, which I believe is related to a non spherical model of the earth that they believe in. We can safely ignore those comments." So elegant:)

[@Cowtymsmiesznego]

Fun fact - a non-spherical model of the Earth is ALSO useful in some circumstances, but again far fewer than the spherical model

[@bactrosaurus]

​@@Cowtymsmiesznego if you want to build a house

[@Cowtymsmiesznego]

@@bactrosaurus Or make a map that you can hang on the wall

[@thefolder69]

our understanding of projectile motion as a parabola is actually based on a flat earth model - if you actually throw any projectile on earth, as it moves laterally, the direction at which gravity pulls on it changes (extremely slightly unless it's literally thousands and thousands of miles). so real projectiles on earth actually travel ever so slightly elliptically, like an orbiting body would, we just treat the earth as flat for simplicity since the difference would be so tiny.

[@KaidaHirschel]

Electric universe proponents believe gravity is not a force because it is a function of electrical phenomenon (ie, it is calculated from a different force, thus theoretically variable and therefore not a constant). They are not flat earthers. In fact, iirc this experiment is cited as evidence in their favor. (Sorry not sorry im just so annoyed that literally anything that bucks the current paradigm is treated like flat earth. There are lots of alternate ideas out there that deserve a second look, even if for no other reason to help highlight the failings of the current accepted model. Progress stagnates when you stop entertaining alternate theories.)

[@kamikazegargoyle]

steve having a haircut inbetween his two shooting sessions and then editing them together is breaking my object permanence :p

[@gleedads]

I worked with an apparatus just like the higher precision one you show in the latter half of the video when I was a grad student and was TAing a 2nd year mechanics course. I'm amazed you were able to get it to work without much more vibration damping. Maybe our building was shaky. We had to have the apparatus sitting in a big tray of sand (to damp out high frequencies) with the tray resting on a layer of tennis balls (to damp out lower frequencies). Without all this damping it just never settled down to an equilibrium. Then a new building started to be built next door. During the construction we just couldn't run the experiment, no matter what we did to try to isolate it from vibrations. The lower precision setups you show in the first half would be less subject to vibrations from the environment because of the large masses and relatively stiff wires. But I'm suspicious that MyLundScience managed to see an effect. I agree that it is unlikely an electric charge effect. Lead is one of the more diamagnetic substances, but that also seems unlikely to be strong enough. So, I'm at a loss to explain how such a large effect was observed. Lucky air currents??

[@JustWasted3HoursHere]

This experiment is uber sensitive so even the tiniest things can disturb and/or affect the results. For example, even having the air conditioner on or a window open somewhere can affect it. That's no doubt why that smaller version seemed to have its moving parts inside a vacuum chamber.

[@doofismannfred4778]

Not so much a vacuum chamber, but instead just protected from air currents from outside.

[@JustWasted3HoursHere]

@@doofismannfred4778True.

[@bayleev7494]

i did this experiment in my undergrad! it was probably my favourite experiment, not least because you can see exactly where all of your uncertainties are and how it's affecting the result. one thing to keep in mind is the angle of the laser pointer: if your laser is directly in front of the mirror then it'll block the reflection, so you have to offset it by an angle, which will in turn change the relationship between the angle of the pendulum and the position of the reflection on the wall.

[@Sammy.a1287]

Very interesting!!!!🤩

[@mathmeetsmachines]

We actually did this experiment in school almost 40 years ago. My school had a "Gravitationsdrehwaage" that looked like the laboratory one in the video but was as big as your original construction. The experiment was run over the weekend because it was too sensitive to the vibrations caused by footsteps of students in, around, and above the room. It used a light beam to measure the angle, but not a laser. Together with Milikan, the thread jet tube, and the measurement of the speed of light, the Cavendish formed the experimental highlights in our physics course. Unfortunately, none of my children did see any of these experiments in their school.

[@dustinpohl2483]

Gravitationsdrehwaage? Wieso, müssen wir immer so aus der Masse herrausstechen?😅

[@mathmeetsmachines]

Brian: "You're all individuals!" All: "Yes, we're all individuals" B: "You're all different!" All: "Yes, we're al different!" Man: "I am not."

[@mrosskne]

You mean gravity torsion balance? KZbin is an English website. Don't use foreign language words.

[@melonenlord2723]

What was the result? How well did it work?

[@ginnya4246]

I actually did mathematics workbooks as a kid as well, my babysitter would take me to the bookshop and we would pick out newer and harder ones. I loved doing them and I am now one of the top students in my maths and physics classes. It really does make a difference.

[@DrunkenUFOPilot]

When I was 5 or 6, the day before I went to the hospital for a tonsillectomy, my mom took me to a store to choose some coloring books. I grabbed all the math workbooks I could! I also grabbed regular coloring books. I remember fuzzily one with a drawing of a steam shovel in it. Let's see.. I had two math workbooks and two coloring books, so I had a total of.... [scratches head]... seven? No....five? Um.... oh, *you* figure it out!

[@sshuggi]

Steve: "I used to be a bad experimentalist." Steve: "I've gotten so much better at experiments."

[@peterspencer6442]

It's not the apparatus but how you use it that counts!

[@GRBtutorials]

I think he meant he was bad at using the existing lab setup when he studied.

[@Thorsummoner0]

this describes software engineering to a Tee

[@simonleeofficial]

Went to all the trouble of buying copper balls and such, but gave up with a laser pointer and a mirror?? Quite odd.

[@kumarchetan6954]

When I was in school, I had an intuition that it would be difficult to measure G by ourselves without any precise equipment, but when I saw your setup I thought that it would definitely work because of how heavy the weights were. But as you showed the problems with your setup, one by one, I got a taste of how thorough and precise experiments really have to be for them to be of any credibility, even for such a simple case. Great Video.

[@lachlangoulden]

This was one of my favourite labs I did in undergraduate physics, even though we spent over an hour watching a laser move on a wall.

[@mastroitek]

I remember this lab very well, my 2 teamates did not show up, I had to do all by myself, which as you said it is mostly marking the position of a laser on a sheet of paper, but quite boring when you have nobody to chat with

[@lachlangoulden]

​@@mastroitek Yeah that would have been boring. It was one of my favourites because we spent the whole time just talking about stuff. That and It just incredible to measure the gravity between 2 tiny masses.

[@stephenschumacher1414]

The Cavendish experiment was my most memorable and delightful moment in undergraduate physics. Truly amazing to witness AND MEASURE the gravity force and constant.

[@simonelomolino2904]

Actually the mass of the copper balls is present in the equation, only through T, the period of the oscillations, which cointains both the inertia of the system and the stiffness of the wire. Obviously if the copper mass is higher you are gonna get a bigger deflection if keeping the wire the same

[@AnirudhTammireddy]

No. It isn't it'd also change the Theta cancelling any effects of the choice of mass of the copper balls. Only reason for choosing different masses for copper balls is to aide with the precision of the experiment.

[@miot22]

I believe the mass of the “small” balls can come into play by making the torsion bar’s moment of inertia less trivial to handwaive dismiss. Usually, it’s convenient to bias the mass onto the external weights and use small masses on the torsion bar to keep the entire thing as light as possible, thus the moment of inertia can ignored or approximated simply as a uniform rod. The heavier the small masses, the sturdier the torsion bar and wire have to be, now the weight distribution is not only significant but it’s not homogenous, which means first order approximations become less and less accurate.

[@buttchronicle]

His justification for the mass of the copper ball not being present in the equation was that it made sense because the mass of objects falling on earth doesn't affect the speed at which they fall (or something like that). But isn't that because the mass of objects falling on earth is generally insignificant compared to the mass of the earth....so can be ignored. Here the mass of the copper and iron balls are similar enough that they both contribute significantly to the gravitational force between themselves don't they?

[@simonelomolino2904]

@@AnirudhTammireddy yes it goes into theta, that's what I called deflection angle, in particular it increases it making it much easier to see and measure

[@simonelomolino2904]

@@buttchroniclethe mass would cancel itself out if we were measuring the acceleration of the copper balls, but we are performing a static experiment(finding where the equilibrium position is), so there is no cancelling out of the mass when comparing gravitational and inertia forces

[@lordiblees]

This is one of my most favorite experiments. As a teenager, I really looked up to Cavendish. The idea that you could "weigh" the earth in a clever setup in a lab was just so mind-blowingly spectacular to me.

[@robertfrysch7985]

Note that the angle theta does depend on the smaller mass. In your equation this mass is just hidden in the period T.

[@TehSlan]

Thank you! I was very confused because yes, objects fall towards earth at the same speed, but the force on those objects is not independent of mass at all, so his explanation of why one mass isn't included confused me more. Makes more sense that it's because the mass affects the oscillation time.

[@robertfrysch7985]

@@TehSlan The question is always, which force is compensating the gravitational force and on what does this compensational force depend on. Also the gravitational force/weight force in the free fall experiment is not independent from the object's mass. The reason why objects have the same *acceleration* when they fall down to earth (in vacuum) is that the inertia force (which is the only force that compensates the gravitational force) is also proportional to the object's mass. However, in the Cavendish experiment the torsional reset force that compensates the gravitational force is independent from the mass (but depends on the displacement) and consequently, the displacement depends on the mass.

[@jaygeorge2262]

Love how you have different hairstyles throughout the explanation. You are gifted. Merry Christmas, God bless you.

[@Taric25]

Even his hair oscillates between long and short, just like the gravity apparatus!

[@tejassonar217]

Sudden haircut at 2:08 surprised me even more 😅

[@francescorusso7730]

I did It in the didactical laboratory when I was a First year undergrad student in physics more than thirty years ago.

[@00alexander1415]

Learned a new Verb today thanks to this guy: "Boyoyoings" Also are those cannonballs?

[@QuantumHistorian]

Wow, wasn't expecting Simon Foster to get a shout out like that! He was great at both doing outreach at Imperial himself, and teaching students how to get do it themselves. I'm delighted to hear he's still going strong.

[@r.markclayton4821]

Did this experiment at University to determine [big]G and got an amazingly accurate result without fudging the figures.

[@bretfuzz925]

I looked at your original setup and concluded the value of r for yours was much greater than the other KZbin one. This may have played a role in not observing rotation. Then, seeing the one with the laser system really cleared everything up. Excellent demonstration and very cool!

[@DerNesor]

I remember doing this in University. The cavendish experiment just hangs in the corner of a seminar room all the time... menacingly.

[@user-zz3sn8ky7z]

I love how this is a pretty much universal experience

[@doofismannfred4778]

There's a modern replica of Cavendish's apparatus over at the University of Tennessee (I think it was at 2/3 scale). A KZbinr by the name of BlueMarbleScience put it together with a little help on the suspension mechanism. He's got hours upon hours of running it and measuring big G with exceptional precision and accuracy. It might be worth a look if you have a moment to spare for a modern construction of the original.

[@radarmusen]

It is an impressing device bluemarbel has made he try to learn flat earther about it but they will not believe anything.

[@doofismannfred4778]

@@radarmusen True. One of them commenting in another thread on this very video has said that weight being a force is "just a claim." They will go to extreme lengths to not learn.

[@アイスクリーム-u8s]

@@doofismannfred4778 They’re so unbelievably hypocritical and irritating. The audacity to say that gravity is “just a claim” while having an entire belief system that is also just a claim created for the sole reason of mistrust.

[@HeatherHolt]

@@doofismannfred4778anyone who truly believes the earth is flat I just cannot truly believe they believe it. I just cannot dumb myself down enough to even comprehend they’re being serious. It’s baffling. It’s the most insane conspiracy theory to me, even more so than lizard people or mountains are trees.

[@broccet]

"Just like how a stiffer spring boi-oi-oings more quickly"

[@dredaxgaming6099]

Bro got a haircut mid video 6:12

[@humanvoicemail5059]

Yoooo😂😂😂😂😂

[@WildCP]

Glad someone else noticed it

[@KeplarDesign]

I thought Cavendish was the guy who invented bananas 🤔

We did that in a amateur astronomers club back in the nineties. The Wire was about 15m long, hung in a Staircase, the masses where about 20kg and you could still see every train passing by on the c.a. 1km far railway in the plot.

[@bend.manevitz8261]

I don't understand why increasing the mass of the hanging objects wouldn't help the experiment. I understand that the additional gravitational "force" would be countered by the additional force required to move the mass, but wouldn't the total force matter when it comes to overcoming the tirsuonal resistance of the wire?

[@b43xoit]

I think you're right. He must have erred in laying out the math in which that mass seemed to cancel. It would make sense if acceleration were being measured, but it's force that's being measured.

[@larrywiniarski1746]

I'm not sure, but I don't like his explanation either, however; I think a larger mass WOULD help...if the wire could hold it. I think for a given wire, you want as heavy of mass as possible that the wire will hold to get the greatest gravitational deflection. The (unsaid) problem is that a larger mass requires a larger wire which is stiffer and will deflect less, so it kind of cancels out. In fact I suspect that it's worse in that the torsional constant is much stiffer. This is because the larger diameter wire has more material further away from the center of the wire so it's torsional stiffness might go as d^4 where strength as d^2... whereas for tiny hanging weights you can use something as small as a human hair.... so in the end he is right....smaller balls+smaller wire = more deflection....but I don't think he explained it very well. Having said that...wouldn't a longer wire be better? I would think that a wire 2x as long would have 1/2 the stiffness and deflect 2x as much.....yet still be strong enough to hold the hanging weights.

[@larrywiniarski1746]

​@@b43xoit The math isn't "wrong", but it might be a little misleading. . If you put a bigger hanging mass you will get a bigger deflection and a longer oscillation period....Yes it cancels out, but it's also easier to measure. That doesn't mean it doesn't matter. Likewise his math ALSO shows that it is independent of the torsional stiffness of the wire....but again common sense says you want a thin wire for a large deflection. Sure you could theoretically do the experiment with a tiny weight and big fat wire .....but it would be ridiculously hard to measure the infinitestimal deflection and it only wouldn't matter to the mathematician.

[@mrosskne]

Run an experiment to test this hypothesis and let us know.

[@anthonylipke7754]

Density and shape seem like immediate differences in the setup. ~7.8 iron ~11 lead the square blocks are going to have a center of mass that's much closer to one another. I'm really focusing on the distances between the centers of gravity.

[@anthonylipke7754]

Now I'm imagining one of the masses being a toroid.

[@robertsneddon731]

Cylinders made from tungsten, perhaps? Denser than lead (ca. 19g/cc) and AFAIK not magnetic.

[@anthonylipke7754]

@@robertsneddon731 cylinders pair with toroid's would be nice. The density helps with the mass center having a shallower surface. I think it still contributes even if the centers can pass through one another.

[@coolj4m]

Actually at 4:33 where you say the mass of the copper balls doesn't come into the equation for G, I think this is not quite correct because the oscillation period T is proportional to the square root of the copper ball mass m (assuming the rod without copper balls has zero mass). So G is in fact proportional to G ~ 1/(M*m). T does not only represent the stiffness of the wire, but also factors in the inertia of the rod.

[@0cgw]

BlueMarbleScience has made a beautiful copy of the Cavendish experiment from scratch (a copy Cavendish's original design) and used it measure G to within a few percent. He has a large number of videos on this in his KZbin channel. The apparatus is now housed in the physics department of the University of Tennessee.

[@declanwk1]

that is very interesting, could you provide a link to the videos, I have tried a search on KZbin but not finding them.

[@0cgw]

@@declanwk1 I hope you'll be able to see this link. It's the initial plans for the experiment. BlueMarbleScience has about 34 hours of live streaming getting the data (including detecting an earthquake) and 14 episodes showing the construction. The apparatus found a new home at the University of Tennessee. kzbin.info/www/bejne/hobSXpasfs2Hh8k

[@TobyAsE120]

I studied physics and there is a lot of stuff you learn. But I think the Cavendish experiment is my favourite "simple" experiment out there.

[@melonenlord2723]

So do you know what could went wrong in the home made experiment?

[@michaelglatz1145]

Correct me if I'm wrong, but I'm pretty sure the weight of the copper balls actually is part of the equation at 4:15, since the time taken for this type of pendulum to oscillate is dependent on the mass of the balls

[@josephbrandenburg4373]

it certainly has that effect on me

[@WilliFromEarth]

We did the experiment with the mirror attached to the thread and the laser (pointer) in our physics 101 university class … in the 1980ies. Still impressive 40 years later. Thanks for this great video showing all the pitfalls of experimental physics.👍😉

[@iagobkstar]

I did this experiment about 10 years ago in my classical mechanics labs with a similar setup, and for sure it's a minute effect. MrLund's video instantly made me raise an eyebrow, such strong gravitational force would crush us into the Earth.

[@AmongSusOfficial]

2:55 boyoyoing 😂😂😂

[@nommindymple6241]

Foster's experiment at Imperial College London (7:32) "fixes" the one issue I had with the other experiments: the possibility of a Bernoulli effect between the masses from any stray breezes. Foster isolates the pendulum masses behind plexiglass (at least I think he does).

[@shnrbtlle18]

I love all the great science stuff, but above all that, I love a great sense of humor, "a stiffer spring boyoyoings more quickly" had me laughing so hard, lol!! Great gravity visual, I did enjoy the video.

[@marasmusine]

Take a shot everytime a flat earther commenter says its because of air currents or static electricity despite all the precautions in the experiment.

[@carlbrenninkmeijer8925]

Thank for this so fundamental experiment. You ought to get a "Show it, Do it, Explain it" Nobel Prize for your outstanding work! I mean it

[@semitangent]

NIce! We had a Cavendish experimental setup in our high school in Germany ("Gymnasium", to be precise) and we used a tiny mirror connected to the twisted wire to project a spot of light across over to the other wall to make the rotation more visible. Good stuff! Although now, that I see the Leybold sticker on your setup - I think we might've even had a similar setup at school...

[@skaaly]

When i was fishing my undergrad for my undergraduate in Minnesota, we performed this experiment in the field house using a pair of crane wrecking balls as the big boys and constructed the smaller spheres out of aluminum cans pressed together by a press mold the engineering and fabrication dept created. It was enormous and very interesting. I am not a doctor.

[@Gunbudder]

i LOVE this experiment, and have always been fascinated by it. i used to think that gravity could be "overshadowed" by larger masses, and reading about this experiment wrinkled my brain hard. i love it

[@johnchessant3012]

That's an awesome result from the lab experiment! Did you figure out what was going on with Lund's setup, if it wasn't gravity, magnetism, or electric charge?

[@bholdr----0]

Instead of using smaller masses on the moving portion of the setup, which would allow a thinner wire and thus a more sensitive experiment, couldn't the wire used just be longer instead? I'd think that heavier masses, though less sensituve, would be less prone to interference from outside factors (anything from air currents to electrical currents from the wiring in the walls, even the earth's magnetic feild would potentially be a relitively strong force in a case like this- trying to measure the weakest physical force on such a small scale... Or would that make no difference?

[@melody3741]

It sounds fake and like it was actually magnets lmao but I dunno

[@nikkiofthevalley]

​@@melody3741It isn't. Lund's video isn't fake, it's just most likely wrong on what caused the movement.

[@harsimran1]

Look at Lund's wooden beams. They are twisted and not parallel to the ground. The weights try to correct this, but the fact there is some natural correction going on, means there is tension. So yeah, all this is bullshit. Even Cavendish's experiment.

[@2birdbrained4u]

@@harsimran1How do you come to the realization that Cavendish's experiment is bullshit when the lab experiment worked very well? He got a very close result to the real G.

[@xe4productions209]

I remember trying to get the cavendish experiment to work in my senior lab for multiple days and failing every time. The issue was every time I moved the larger balls, the vibration was enough to completely destroy any positive torsion motion, and I could never get the oscillation amplitude to increase enough to get workable data. I eventually gave up and did the Millikan oil drop experiment instead because that has an easier experimental setup and procedure even if the data analysis was harder. Looking back, that should've been the first sign I was going to become a computational modeler rather than an experimentalist.

[@RibusPQR]

You did the Cavendish experiment instead of the Cavendish experiment?

[@xe4productions209]

@@RibusPQR Whoops! I meant to type Millikan instead! Thanks for pointing that out.

[@Galileosays]

Great to show the sophisticated modern set-up of Cavendish's balls. Not only we should thank the designer, but also the technician who build it.

[@paparoysworkshop]

The thing I find most idiotic is that those who claim gravity doesn't exist (among other things) think they know more than the greatest minds in physics that ever existed. There is nothing wrong with questioning something, but to put your fingers in your ears and go, "la la la la", when presented with evidence is just unbelievable.

[@logitech4873]

​@@d1g1tvl-0hretor1cmuh paranoid contrarianism

[@just_some_dude_my_guy]

​@@IvanMectin Electrostatics is not a force, it is a phenomenon present with objects under certain electromagnetic forces. The fact you cannot distinguish these is already telling.

[@CNCmachiningisfun]

@@IvanMectin Grow up!

[@nathanbanks2354]

Nice to see someone use copper balls--I never thought of magnetic effects. I was disappointed to see you switch to lab equipment, but this is better than misrepresented results. I'd love to see a version with home-made lead balls & a laser pointer.

[@11moonshot]

me too... but air currents are also a fiendish adversary!

[@OogieWa]

@@11moonshot I also was wondering how he was going to pull this off in a room that uses the building ventilation system.

[@ColmGibney]

Copper isn't immune to magnetism.

[@TylerDollarhide]

It would be really interesting if they perform this experiment on the moon during the Artemis missions. That way the downward gravity is much reduced, and any small air currents are eliminated.

[@AyushKumarSah-g9v]

Thank you much, now I understand Gravitational force way better than before. I appreciate your hard work and you are also very passionate. Thanks a ton!

[@cheeseburgermonkey7104]

"So I bought some really heavy balls" -Steve Mould, c. 2023

[@mralistair737]

"by the power of buying tow of them"

[@YayComity]

Good thing the shipping costs are tax deductible.

[@ronald3836]

Now Steve can proudly declare that he has balls of copper.

[@researcherchameleon4602]

The flat earthers are going to have a stroke reacting to this

[@briangates6707]

When I was at school we used spherical flasks full of mercury, I can't see that happening now.

[@Woodside235]

Why not? Once you're done with the experiment, you get a nice refreshing beverage!

[@toxanbi]

At this level of such small differences in resulting gravitational attraction forces additional forces caused by light pressure (radiation pressure) can come into effect.