Watch gravity pull two metal balls together
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- Опубликовано: 15 май 2024
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The cavendish experiment shows that even the very week force of gravity can be seen between two room scale objects. Even with the naked eye.
MyLundScience's video on the Cavendish experiment: • The Cavendish Experime...
A video derivation of the Cavendish experiment equation: • The Cavendish Experime...
Experimental procedure: www.ld-didactic.de/documents/...
Equipment user manual: www.ld-didactic.de/documents/...
Chapters:
00:00 the beginning
00:44 The Cavendish experiment
07:30 I get it working!
Corrections:
4:53 This isn't a fair comparison. Actually, if you changed the mass of the hanging masses in the experiment, it WOULD change the deflection angle. That's because the value of T in the equation would change. The torsion pendulum would oscillate more rapidly with lighter masses. Thanks James Gilbert.
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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.
Great video once again Steve. You were mentioned in a question in my school's yearly Christmas quiz, seeing at you went there.
How do we know if the masses move towards each other due to gravity or the motion results from the rotation of the earth?
@@piranhaofserengheti4878 Similar reason why a magnet sticks to the fridge even though it's still pulled down
Would using flat objects instead of spheres make a difference?
@@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)
I’m glad you showed your homemade experiment even though it didn’t work. That took balls.
of 14kg steel
I wish I had those! 😃
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.
r/techicallythetruth
Giant 14kg iron balls
Great job, Steve! 10% error is typical for what physics majors get when they do this lab experiment using the 2nd apparatus you used.
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?
@@tormodhag6824 yup, and then you find out more precise G :D
I was thinking similarly - with a measuring rule on the whiteboard and a time-lapse overnight 😀
@@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".
@@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!
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
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.
sounds like anybody could do it
@@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.
But it's only really useful if you know what went wrong.
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)
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.
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
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!
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.’
@@pyropulseIXXI :( Yeah it is weird to me too but that's just how it is in Asia
A spring “oioioing” is the technical term
Yeh, I loved that!😄
I was not ready for that 😅
He genuinely made me boioioing as well 🤣 it's called laughing.
i refuse to not believe that
That perfect balance of technical and just really likeable
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.
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.
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
(where gravity is shielding from cosmic radiation gravity can never exeed the speed of light )
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.
I wish I knew about this experiment when I was a teenage flat earth tard. Would have saved me a year or 2 😅
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...
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.. 🤷♂️🫠
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!
"static electric shock"
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! :)
And he grew some serious facial hair in those same 7 seconds too!
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.
That has got to be a lucky catch. Amazing!
Earthquake detector. 😊
wow, that's really cool
That's awesome!
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).
Mould's Law: a stiffer spring boyoyoings faster
Pretty sure it sproings quicker too.
Man you beat me by an hour lol. Well done
Thats what my wife says
Literally made my day! 😂
@@heatshieldthis is a place of science , stop this mumbo jambo
"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:)
Fun fact - a non-spherical model of the Earth is ALSO useful in some circumstances, but again far fewer than the spherical model
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?
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
That would be cool!
Or e!
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.
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).
g is easy to calculate, G is much more interesting
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.)
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.
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!
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.
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.
@@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.
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.
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!
And yet he still didn't wait for it to fully stop, completely invalidating this silly 'experiment'.
“the boi-oi-oing” 😂😂😂
Well said! Efficiently and effectively conveyed what you were talking about. Honestly brilliant. 👏👏👏
It should be adopted as a scientific term, like "spaghettification".
Came straight to the comments when he said that 😭
Now I know what that is called.
Amateurish and childish. Obviously this channel is meant for small Children
@@kenfryer2090 troll
2:51 That boi-oi-oing was so well delivered, I felt the springiness within
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.
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.
Thank you for not disturbing your nice video's with background music, like so many others do.
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!
Cary!! I miss you! Are you still posting videos? I will now go and find out
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…
i cant believe they made a human named after the dwarf planet
Unless they aimed the laser perfectly, it would be applying force to the mirror. It would be a terrible light sail.
Photon pressure from the laser could affect the reading.
This is such amazing timing. I was just reading about gravitational forces. Seeing such a perfect video released so recently is great
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.
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!
He is so dedicated, his hair cut was oscillating the entire video.
lol, not everyone noticed that
Ha ha nice one.
Took me so long to find a comment saying this, as I thought I was just being crazy
I noticed it and i was so confused
👍 I thought I was the only one who was wondering...
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
Wow, very impressive for 8th grade! Very cool.
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.
"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.
Finally, someone on RUclips 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.
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.
@@joeomundson
Its not that glaring since the video was playing at 30x speed
If Steve also dropped rocks from a height, found g, and then calculated the mass of the earth, it would be doubly cool.
@@-ZH I know it was sped up but even still the magnitude seemed like a lot
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.
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.
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
Great Video indeed. Hope you will bring such interesting videos for the physics enthusiasts. Thank you Steve.
2:49 petition to make
boi-oie-oing the official scientific name for a spring springing
having a conniption over if it’s oi or oie someone let me know 😂
who do we need to talk to to get this to happen
like the SI or something
@@vigilantcosmicpenguin8721 prolly faucci 🫠🤣
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.
wouldn't the charges neutralize once the two masses made contact?
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
@@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.
@@carlosgaspar8447he said pvc pipe not the mass
@@Repent-and-believe-in-Jesus1Nobody asked xD please dont spam random videos
That's cool, you took me back to an experiment I did during my first year physics university-study. Thanks for re-experiencing me this!
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.
Steve explained gravity so hard, his hair went back inside his head.
truly a big brain moment.
Ikr. I was so into it but totally got thrown off by the haircut 😑
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.
2:55 boyoyoing 😂😂😂
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.
In Finland, in 80's Tampere University students were defining gravitation constant on a first year laboratory work course just as described here. Nice and easy task to do and result was quite accurate.
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.
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.
Heavy and dense masses, e.g. tungsten balls are better than iron.
Or you could use yo mama for the stationary mass. She brings a lot of mass to the party.
Wouldn’t the best way to do the experiment be to do it in a vacuum?
the effect of air currents is removed by placing the central setup in a box
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...
Incredible story and work. Thank you for your contribution to science and humanity. I hope he sees your comment and gets back to you!
is synthetic aperture radar on satellites used for this now?
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.)
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.
the money didnt run out, ....the military took it and said "thank you", its prolly been improved and part of a top secret program
I remember doing this in University. The cavendish experiment just hangs in the corner of a seminar room all the time... menacingly.
I love how this is a pretty much universal experience
My A-level physics class had access to a set-up like Cavendish's in the late 1960s. Our measurements were miles out but there that there really was a force was clear.
Getting not just the order of magnitude but also one significant figure in the lab is bloody amazing, top job
Sure. But the scientists get the credit there. Steve just turned up and used their kit.
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.
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.
After all time and effort these brilliant figures have spent to make this experiment, some people still think gravity doesn't exist
So cool to see practical experiments working how they should!
Bro got a haircut mid video 6:12
Did anyone else notice that he got a haircut between shots at 6:25?
😊
Even before that. He jumped before and after
This takes me back to doing this experiment as an undergrad... they made us derive the equation too, which was a nightmarish construction involving over a dozen variables.
Considering you guesstimated both the equilibrium points I’m AMAZED that your number was so close!
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 😀
No way, I'm an ICL Physics student, too!
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!
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.
Ah, the perturbation of air currents as a result of the stationary bricks could well have been the cause of the deviation.
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.
@@poznaniak8349 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.
This is nothing but electrostatic attraction.
Gravity is a myth.
If you can't measure it, it's not real.
Cavendish was a fraud.
There is no way his crappy experiment worked.
We are trapped in lower earth orbit.
No one leaves lower earth orbit.
Nasa is a fraud.
Nasa is a giant CGI factory.
Check out a list of nasa vendors and see where they spend our money.
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.
So do you know what could went wrong in the home made experiment?
We had that EXACT experiment at my Comp School for 'A' Level Physics in 1974!
Unfortunately, the bar & balls were suspended from the ceiling DIRECTLY under the stairs!
So, we had to do the experiment on Wednesday afternoon, when the kids were out for Sport.
As I remember, we DID get values very close to the known Gravitational Constant.
They probably do a "computer simulation" of the Exp, these days.
We also had the 'Millikan Oil Drop' equipment for finding the charge on an electron ... ANOTHER result very close to the known charge of the electron!
So cool, thanks for the top quality every time!
Oh, hey, it's the marble guy.
This is a guy who knows his balls
But the question is, can marble machine 3 play tighter music if it takes into account gravitational forces?
Thank you for your beautiful musical videos!
@@amosbackstrom5366 🤨Dude, it's marbles
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.
I wonder if there could be some beta decay generating electrons.
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?
@@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.
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.
@@bluesbest1 oh but of course, thanks for pointing out
This is one of the experiments my uni offers in the lab courses for physics bachelors. It's probably the most hated experiment among students because of the time it takes. Luckily it was taken off the roster when I did my labs so I only heard stories about how tedious this apparently was. I'm glad I got to see the experiment like this, and at a fraction of the time too!
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.
"Just like how a stiffer spring boi-oi-oings more quickly"
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.
Very nicely done!
You're a freaking genius, mate! Absolutely love your videos. Nicely done.
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."
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?
Best thing I heard all day. "A stiffer spring boioioings more quickly."
@@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."
@@omp199I'm only going by the (UK) book version, which I'm sure said, "Massed."
@@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.
steve having a haircut inbetween his two shooting sessions and then editing them together is breaking my object permanence :p
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.👍😉
Flat Earthers be like: That is static electricity, not gravity
02:50 I think "boi-oi-oing" should be the technical term for a spring releasing tension
I second that. Boi-oi-oing should be in every scientist's vocabulary from now on.
Agreed
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.).
2:50 I liked his use of onomatopoeia for describing the spring. 😄
A very good video, it shows us the difficulties in making accurate measurements and how to prove if experiments are really working.
Steve: "I used to be a bad experimentalist."
Steve: "I've gotten so much better at experiments."
It's not the apparatus but how you use it that counts!
I think he meant he was bad at using the existing lab setup when he studied.
this describes software engineering to a Tee
Went to all the trouble of buying copper balls and such, but gave up with a laser pointer and a mirror?? Quite odd.
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.
I really enjoyed this - thank you
Great video! I'd love to see you repeat your home experiment using the laser measurement system to see if you could measure the tiny fraction of change in theta with it.
Interesting to note that "Objects fall at the same rate regardless of mass." Is only true when the difference between the mass of the two objects is so great that the gravitational effect of the smaller object is negligible.
I came here just to say this.
I think the original statement is more true than you give it credit for. The acceleration of an object at a given time truly is the same regardless of the difference between them
@@skya6863the acceleration is the same, but the forces are different
Or the bigger object is fixed by something else (as is the case here, the gravitational effect of the small object on the big one will be fully compensated by friction).
@@skya6863 Take note the Earth is 'rising up' due to gravity that the small object exerts on it as well. The small object's acceleration is constant no matter what it's mass is. But the Earth's acceleration increases the larger the small object's mass. So the relative acceleration increases the larger the small objects mass.
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. Now everything is at the same charge.
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.
I think if you attach the torsion rod to the masses it will change the torsion. it has to spin freely
Yes, or just touch them together once so that their charge equalizes.
@@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.
@@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.
Very nice to see an actual demo of this famous experiment. Makes you appreciate how determined and meticulous Cavendish must have been. I guess being one of the richest men in England probably helped a little!
wow this was nice! :D i've been reading up on GR starting from newtonian gravity history, and yours was a help to show what cavendish did was so revolutionary. this was the first experiment that calculated the actual value of G, before which it was just indirectly estimated using the gravitation force F=GM/R^2
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).
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.
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.
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
I'd replace the iron balls with lead ones (or gold ones if it was a government project).
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.
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.
Gravitationsdrehwaage?
Wieso, müssen wir immer so aus der Masse herrausstechen?😅
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."
Flat earthers who don't believe in gravity would never take the time to do this experiment but I can imagine all their "criticisms" lmao
Oh, a few have dropped by. Claims of electromagnetism aplenty.
I'm a flat earth person, and I appreciate this video
I did It in the didactical laboratory when I was a First year undergrad student in physics more than thirty years ago.
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 RUclips channel. The apparatus is now housed in the physics department of the University of Tennessee.
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.
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
@@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.
My guess on why Mr. Lund's experiment worked "better" is that he used flat surfaced objects, and you used spherical objects. Therefore, your center of mass was considerably farther away than the physical distance between the objects than Mr. Lund's were (and maybe the wire was just too thick as you stated). As with the lab set-up, it appears more precisely made; more dialed in.
Awesome job Mr Steve.
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.
Not so much a vacuum chamber, but instead just protected from air currents from outside.
@@doofismannfred4778True.
Learned a new Verb today thanks to this guy: "Boyoyoings"
Also are those cannonballs?
"And so, I bought some very heavy balls"... hahaha love a Steve Mould video!
Insanely impressive! well done!
I looked at your original setup and concluded the value of r for yours was much greater than the other RUclips 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!
"So I bought some really heavy balls"
-Steve Mould, c. 2023
"by the power of buying tow of them"
Good thing the shipping costs are tax deductible.
Now Steve can proudly declare that he has balls of copper.
More videos like this please!
"boioioings more quickly.", I love it! 😍
1:45 that's what she said 😂
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.
A nice feature of this equipment is that it self-compensates for changes in the direction towards distant masses, however large, so you don't have to take the tidal force into account.
Your videos are bloody fantastic. Thanks steve. Keep up the awesome educational content. Really bloody hard to make these topics interesting.