Steve Mould - 2023-11-30
The first 100 people to use code SCIENCE at the link below will get 60% off of Incogni: https://incogni.com/science Thanks to Hugh Hunt for the idea for this video. If you try to pass a bouncy ball under a table, if it hits the underside of the table it will just bounce back out the way it came. Here's the golf ball paradox video: https://youtu.be/5sbM2Isx17A Here's the turntable paradox video: https://youtu.be/3oM7hX3UUEU Here's my discord server: https://discord.gg/B6uNzAgshy Here's Patrick's simulations: https://www.glowscript.org/#/user/Patrick_Dufour/folder/spinningstuff/ Here's the video Eyy Tee sent me of the ball in a square box: https://www.youtube.com/watch?v=AfPhuwBItB4 You can buy my books here: https://stevemould.com/books You can support me on Patreon and get access to the exclusive Discord: https://www.patreon.com/stevemould just like these amazing people: Alex Hackman Glenn Sugden Tj Steyn Pavel Dubov Lizzy and Jack Jeremy Cole Brendan Williams Frank Hereford Lukas Biewald Damien Szerszinski Marshall Fitzpatrick Heather Liu Grant Hay John Zelinka Paul Warelis Matthew Cocke Nathan Blubaugh Twitter: http://twitter.com/moulds Instagram: https://www.instagram.com/stevemouldscience/ Facebook: https://www.facebook.com/stevemouldscience/ Buy nerdy maths things: http://mathsgear.co.uk
Now explain why the children’s bouncy ball always gets stuck under the sofa and never bounces out.
It likes it under there
The sofa is just a low table. Otherwise why would there be so many crumbs in the cushions?
osmosis
Gremlins
Electrolysis?
That’s also related to the “impossible” shots in snooker and other billiard games. When cue ball suddenly reverses its direction due to the spin gripping the cloth or cushion.
this is more like a ball coming off the rail with sidespin
@@cage989 yes, that’s what I’m talking about. If you inspect a masse shots with a lot of spin, it’s essentially the same forces of friction that reverses the direction of the ball after gliding on a flat surface. It’s probably possible to replicated it in 3d by using slippery or magnetic surfaces that ball bounces off, but essentially you can see these effects in games like baseball and golf, when spinner ball runs on curve by catching air molecules.
The "impossible" snooker shots also use the fact that there's a difference between static friction and sliding friction. And because change between those happen pretty abrupt when force remaining in the ball decreases (thanks to sliding friction), the ball seems to suddenly change behavior in the middle of the shot which gives the "impossible" appearance.
@@Vlow52 the cueball slides along the surface before coming back with backspin, it's not the same as a ball changing direction immediately when coming off a rail with side spin
Does that include making the ball jump as well?
Before getting caught up in the many-sides version, I think it's important to mention that part of the reason it's hard to bounce a ball under a table is that the rotation robs some of the horizontal velocity, making the ball hit the underside of the table much earlier than you think it should. You have to bounce the ball considerably farther away than half way under the table for it to come out the other side.
Basically what i was thinking, if you made sure it bounced after the middle of the table (maybe with an extra outwards rotation) it would most likely just pass through.
Yep. Where I was caught flat-footed is how often it does this effortlessly (I actually tried it). I figured that it would nearly always bounce under the table and across the room unless you put some back-spin on the ball. Nope!
I think the implication was that the ball would hit the bottom and top at least once.
@@repentandbelieveinJesusChrist1
“Beware of practicing your righteousness before other people in order to be seen by them, for then you will have no reward from your Father who is in heaven."
Matthew 6:1
@@repentandbelieveinJesusChrist1
🎶He's got the whole world,
In his ass...🎶
I play racquetball, which is basically a bouncy ball in a cube like this. I remember when I was first learning, the ball kept bouncing off surfaces in ways that seemed more extreme and counter intuitive. It's second nature now, but this video was great at explaining what my brain had trouble with all those years ago!
Came here to say this. This is the principle of my Z shot where I can make the ball go parallel to the back wall leaving only a couple inches between the ball and the back wall. If you play with an old ball or moist walls, the ball doesn't spin right and doesn't "Z" properly.
I love how well you keyed out your hand on that slo-mo shot, what an editor!
Some recognition at last. Thank you
i saw a blur.. had no idea it was his hand.
He keyed out his hand? Wow! I never noticed it! It was simply too good.
Duh, he never keyed out his hand, its just a camera that records at 100000000000000 fps, so he just threw the ball and recorded it with that camera. He sayed that he keyed out his hand because he didn't want us to know that he has access to governments secret objects. Simple as that, he is the president of US
which second is that?
oh nvm it was a joke xD
"Low-poly cylinder" is my new favorite name for convex regular polygons.
You brought up friction at the collisions, but I kept wondering if you were going to address deformation of the ball at each bounce. My initial thought is that the ball deforming when it hits a surface mostly just increases the surface area for friction to be applied, but I don't know enough about bouncy ball physics to decide if it is a crucial part of the dynamics or not.
Everything is crucial if you're being precise enough.
You're definitely misusing the phrase "convex regular polygon" here.
@@ewthmatthYou're right. Convex regular polygon prism?
@@Lombardio Just "prism" would do fine.
Deformation is crucial for two reasons: (1) forces need area to transfer between objects (i.e. stress), and (2) the total linear impulse is a function of the friction force and the duration of the impulse. If the ball was too stiff, the friction force wouldn't have enough time to change the linear momentum enough to bounce the ball out.
Now explain why my wife left me
Ouch
Prob your wife is the ball, cuz she doesnt want to be with ya.
skill issue
@@gentlemanthesavior9601the ball come back his wife didn't
Cause u keep watching YT videos instead of paying attention on her.
Incredible video! I remember the golf ball video ages ago. While your communication skills really carry your conveyance of fairly complex ideas in an intuitive and digestible manner, this video was the key to understanding that video fully. Once I "got" this video, it instantly allowed me to understand your previous. Excellent work, as always! :)
I bet if you did this demonstration with a ball covered in different coloured spots you'd get a nice visual indication of the change in rotational axis after each collision. The various spots would move more or less depending on how close to the axis they are and after a bounce a different spot would stop moving
That would help immensely with the animated example since you really can’t see the spin because there’s nothing to track on the surface
I'm fairly certain soccer ball design on bouncy balls exist...
Zigzag stripes is best for viewing rotation on a sphere.
@@nicholasbyram296I was also thinking stripes. Doing the experiment with all 3 designs would be fun.
Steve, you are one of the best science communicators I've ever seen. So glad that you make these videos. Your kindness and endless curiosity are greatly appreciated.
seriously one of the few channels where whenever I see a video being recommended I cannot resist. It also never feels like a waste of time watching them
I'd say Steve Mould and ScienceClic are equally good at converting complex topics into something intuitive.
What I appreciate is that he communicates things in a manner which someone with no background in science can follow, but then an expert can also appreciate the content as well. I'm an aspiring professor of engineering, and Steve's delivery is something I've been paying close attention to so I can be a better teacher.
He nails it on a level that only people like the curiosity show and Bill nye have matched,
Absolutely true. I have been really disappointed by some other channels losing sight of their purpose, but everything I've seen from here remains focused and thoughtful.
This is so simple and logical, but I never even stopped to consider this might be happening when you throw a ball to bounce on several surfaces. Would be nice to see a similar experiment with a gyro-type of bouncy ball that tries to eliminate this change in spin
one could maybe apply lubricant to the ball
@@bluesight_❤
its pretty amazing how much you can learn from watching things in slow motion. like you can say it to me and explain it super well but showing it to me in slow motion I actually can rap my head around the ball rotation and the effects that has on each bounce. played quite a bit of 8-ball in my day and I think that was my biggest hurdle was the massive difference in friction
I like that you use props like a book and a box - it shows people that they can explore physics with the stuff they've already got in their house
physics is everywhere and its fucking sick
Look at this guy, bragging about his books and boxes
So that scanning electron microscope I just bought on Amazon was a waste of cash?
@@ThatOpalGuy nah man thats a certified pimp move my guy
And what a book, eh?
I just want to say, that shot where you show the ball spinning and floating slowly through the air was absolutely brilliant. I still have no idea how you pulled it off.
I sat here for nearly 3 minutes (maybe like 2 minutes and 46 seconds?) trying to wrap my brain around it and couldn't figure it out! Bravo.
You just need a high-speed camera and someone to throw the ball in a few times until you get the shot you want.
@@koriko88lol
@@koriko88it’s a joke.
I think he might have keyed his hand out or something? I'm not sure, but whatever he did makes it such a cool shot.
which shot exactly?
The variables like the materials of the table, floor, and ball are key. If you have something like a ping pong ball and a surface that is slick, because you are reducing the contact friction, you will likely overcome this.
Such a generalizing title, almost click bait. First time seeing the channel and not gonna stick around, no pun intended....
Steve, I so appreciate how you can break something down to make it intuitive! Thank you for the service you provide, which is entertaining, while making something really cool makes sense to people :)
Table Tennis, once you are past the "basement" level, is almost entirely built around this phenomonen. You can pretty easily learn how to bounce a table tennis ball back over the net using the spin alone. the idea that the collision changes the spin is essential to master. super cool video! i bet you could expand this by like filming the spin of a ping pong ball between highly skilled players
Mind blown
I was about to say, this is completely expected. We hit counter topspin balls with our rackets basically horizontal and the ball basically goes back on the exact same arc despite the angle of contact dictating the ball should go the complete opposite direction.
Interesting.
Funby i woukd say a tt ball does the opposite. Back spin serve is back spin firdt bounce server side and back spin still on subsequent bounces due to lack of friction. Long pips reverse the spin due to lack of friction and a direction change. counter looping uses the principle in this vid as your using grippy rubber
As soon as I saw this video, it was the first thing that came to mind, having played over half a century ago with the particularly grippy, even tacky, new Butterfly surface. (I'm avoiding naming specific products).
It was the most natural thing to be counterdriving almost directly forward with a blade that was almost parallel to the floor into a topspun ball traveling directly horizontally at the top of its arc, if that incoming ball had a high enough bounce.
As someone who plays table tennis, this is very intuitive but incredible nonetheless.
Exactly what I was thinking. Receiving a top spin always makes the ball want to bounce up, etc.
Try it with a bouncy ball... You will do some ''impossible'' shots. I was wondering about the extreme lightweight smooth ping pong ball... I bet that will bounce under a table.
yeah, although this is somewhat "reversed" and "amplified" - it's the ball that is tacky - not the surfaces and due to higher inertia of the ball it does not die down as fast as table tennis ball
I appreciate how much info you added that isn't just answering the prompt of the title.
Also taking a limit as teh number of side approaches infinity is a cleaver way to figure out the relation between the under table bounce and the golf ball paradox.
Steve, you're soo good at teaching. I appreciate this channel a lot.
The part where you're moving the ball in slow motion in 3:00 just made me smile. I can just see the dedication in trying to show everyone how the dynamics work. 😊
But wouldn't that be wrong? The spin increases the angle of motion thus there is angular momentum and newtons third law states there is an equal opposite reaction. Idk everything so please Correct me if im wrong
I would love to see a practical follow-up about putting an initial spin on the bouncy ball so that it continues out the other side of the table.
Is there a way to do that? The initial spin would just make the returning force (when it hits the table top) stronger. Unless you spin it so hard that it misses the table top already after the first bounce.
@@u1zhaI've repeated the experiment with different balls, and got mixed results
I also really want to know if this works
@@tafazzi-on-discordthe high friction of the ball against most surfaces is the reason for all this behaviour. I'm halfway into the video and I'm a bit surprised he hasn't mentioned that yet
Or just not bouncing it so hard. I feel like all these commenters are too wrapped up in science and havnt played any games or sports..
I've watched several of your videos related to fun objects that you've made transparent, but I never realized how much physics you also do on your channel.
This video was so clearly explained and interesting. I'm a none science person and I really feel like I could show this to my 5 year old and understand the concept. This kind of knowledge sharing is essential for humanity Steve. We are all smarter because of your efforts.
Interesting observation I had in that demo was it felt like the change of direction was happening on odd number faces. Wonder if it's conincide or there is some maths there. Would love to see the experiment with 3 faces and 5 faces.
My guess would be that each tube has a consistent and particular face that causes the change of direction. For the square it was the third face, for the octagon it actually looks like it’s the fourth face (but it’s hard to tell - it might be the third one).
Certainly, for the first (2D) example it was the second face
I imagine the designated face will probably be the one that corresponds with the (7*0.5)/2 oscillations in some way.
My guess is that in order to complete a full vertical oscillation, you must complete (7^0.5)/2 horizontal oscillations. And so if you complete 1/4 of a vertical oscillation, i.e. entry to inflection, you complete (7^0.5)/8 horizontal oscillations.
That comes out to about 0.331.
So the ball will have to travel at least 33.1% of the way round before changing directions.
For a square, the first face to be more than 33.1% of the way is the third face. For an octagon, it’s the fourth face. For the 2D example, it’s the second face.
Thanks for the awesome content!
This video is made to easy to understand so nice ❤
Absolutely amazing
Nice
Your videos are always informative and entertaining. Thank you!
my cat really liked this video
Why is this the top comment
This made it so much easier to understand, specifically breaking down the table underside turning around and the square model, I absolutely love this!
A thought experiment: One model for understanding light is that it consists of particles. Light shined on a surface always reflects away at the same angle it came in on. Presumably, if you shoot a light particle down at the floor under a table, it will exit with at the same angle and not bounce around. That's the "angle of incidence equals the angle of departure" rule.
Given all this I wonder what size/diameter of minute particle is required, such that spin becomes a significant factor in the departure angle?
Quantum mechanics is where mechanics break down, to speak in simple terms. First of all, a photon has no rest mass. Secondly, it can't spin like a ball because it's got no dimension. Honestly, it's better to think of it in terms of a EM wave that due to the collapse of the wave function results in being quantised. That's also very simplistic, but it gives you a better analogy in this case.
As for how small a physic object with rest mass can get... Realistically, you'd start having problems with surfaces (and atoms themselves) being uneven before this effect vanishes in the world of quantum mechanics.
@@NoNamer123456789 Thanks for the info. Makes sense. This effect seems also dependent on the actual incident angle, and the relative traction between the ball and flat surfaces. A tennis ball, for instance, seems to have less traction on a smooth surface than a rubber ball, so the surface doesn't impart much rotation to it. I can easily toss a tennis ball under my table at a high incidence angle, and it shoots right out the other side without "reversing." Still, an interesting phenomenon.
Ah yes I concur. Definitely understand what u guys are talking about
@NoNamer123456789 Photons don't spin like balls, but they do have spin, and it does change when they get reflected because their polarization is changed. This also changes their reflection probabilities since the angle of polarization relative to the surface matters.
@@Vexas345 I'm gonna be honest and say that's mostly above my level of understanding, but shouldn't it matter which reflection you mean exactly?
Like, if we take a perfect mirror, for instance shining a beam of light from water to air at an angle that causes total reflection (40 something degrees IIRC), does the polarisation/spin matter?
Wow I remember watching your first video on the cyclinder and not quite being satisfied with my understanding of the physics but it totally makes sense when it's simplified down like this. I'm amazed.
Breaking down the physical components impact to impact (the spin and velocity of the ball) really does help highlight what is happening as we increase the number of impacts/collisions occurring. Reducing to a simplified state sometimes just allows us to understand what is happening and we can build on it like towards the golf ball paradox.
Not sure how or if this applies (haven't watched the original golf ball paradox), but this reminds me of missing golf putts and basketballs touching the entirety of a rim but not scoring. awesome video! keep up the good work.
That is in fact the motivation for the original golf ball paradox! And (obviously) where it got its name.
Every time I miss I'm gonna shout golf ball paradox
This makes the cylindre + ball so much more intuitive. I found the previous video hard to really grasp but now it seems obvious!
This is really amazing stuff
One of the best youtube channel of all time. Love you Steve!
this channel is really fantastic - what an amazing demonstration of thoughtful science
What I love the most about this kind of videos is that they are no longer just science communication, they are also straight up science.
this is not straight up science. This is click bait.
This topic is just far enough beyond intuition that it is fascinating to watch.
Steve Mould... One of the best science explainers on YouTube. And non of the "I am always right" attitude of the notorious Derek.
A fellow schizophrenic out in the wild
Non or none? know or is no the difference?
As always perfectly explained for any audience. I can't help but feel you are going to one day inadvertently solve one of the great mathematical challenges, such as the Navier–Stokes existence and smoothness problem.
He'll demonstrate the Banach–Tarski paradox in real life.
Your slo-mo at 1:05 is enough to see what's happening, to me.
Ball's going a direction, which can be represented by down and right, ball hits the floor which transfers some of the forward momentum into rotational momentum, ball hits the ceiling transferring all that rotational momentum backward, and spinning it the other way, and then since it's spinning the same way it's going when it hits the floor again, it continues coming back.
That's cool.
Dude, I love this channel. It's exactly what I enjoy about being a curious person. You present these fascinating and interesting snippets of SCIENCE! and the world into these moments I can engage with in my day, even though my life isn't particularly involved in these ideas. Love it. Thank you for all you do for us, your fellow curious people around the world.
An effect I noticed years ago with a basketball is that if you spin it and bounce it, it will come up spinning the other way. I never put more thought into it but it's cool to see the changes that a little spin can make.
I thought about basketball, too. This puts a better perspective on why the ball spins out of the rim so much.
There was a paper published in Scientific America in about 1980/1981 that covered all of this including all the analysis you have done in this video. The author even gave some examples of him wanging a ball in a squash court and how it bounced off the walls and floor - he also stated that those experiments frightened him so much he would be reluctant to complete them
Does this hold true for only convex polygons? I wonder how a star shape might behave.
+ i want to see where this thread goes
My guess would be yes. Even with progressively more acute angles within the shape (Circle > Octogon > Hexagon > Square > Triangle) it still works. So a star-shaped polygon would be like 5 triangles put together. A practical experiment could be difficult though.
A very pointed question.
Well in a star shape there is definitely a higher probability of hitting a concave surface that goes against the general motion of the ball. If that happened, I would think that would change the motion of the ball entirely. The challenge would be to calculate how likely the ball is to hit one of those concave surfaces. I would think as long as it hits only convex surfaces it should still work though
Seems like it should work the same in theory, but I suspect it would be difficult to make a physical demonstration. Maybe a computerized simulation with perfectly elastic collisions would work out.
I love this. My 8yo and I mess around with bouncy balls in the house. And I had to explain if you hit the ceiling it'll come back. But I've always wanted to know the physics. The rotation and friction combination is just a cool physics interaction. We actually have some odd shaped bouncy balls, flat edges, egg shaped, etc... and how they make then the physics unpredictable.
@@Juggler534 Haha, our favorite one is shaped like an egg. It makes for fun games of trying to catch it. Also always run the high risk of breaking something in the house.
2:22 is beautiful - such a simple demonstration and so enlightening
This is related a lot to your video of a ball rolling on a spinning table. It shows that the backspin effects each bounce due to friction & change of rotation. I used to play with the spin of bouncy balls growing up. It's facinating
Bouncy balls have a PhD in hide and seek. Prove me wrong.
@SteveMould - 2023-11-30
Does it make more sense now? Maybe. idk
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@ThereIsNoSp00n - 2023-11-30
You could reduce friction between ball and surface by applying a lubricant or talcum powder, thus reducing or even cancelling the effect.
@EquaTechnologies - 2023-11-30
i will stay private with this, yah?
@oznerolk - 2023-11-30
it reminds me of Michael Moschen's "Energy" routine!
@rogerrabt - 2023-11-30
Let's try with a football/rugby ball?
edit: Also what happens in 3 sides?
@swannee69 - 2023-11-30
pool and snooker players understand this principle, the spin reverse the direction when it hits a 2nd cushion