# The Maths of Spinning Coins and Euler's Disk

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**Published: 21 March 2016**- A spinning coin rotates as it wobbles. The rate of rotation is (1/cos(θ) - 1) of the rate of wobble. Draw an arrow on a coin and check it yourself!

The notes from the whiteboard are available here:

imgur.com/a/XVw6m

Here are the videos of the disk spinning:

NORMAL SPEED: it-clip.net/video/dmo0whbDiGQ/video.html

10% SPEED: it-clip.net/video/2Kk0KMQeRCk/video.html

Music by Howard Carter

Design by Simon Wright

MATT PARKER: Stand-up Mathematician

Website: standupmaths.com/

Maths book: makeanddo4D.com/

Nerdy maths toys: mathsgear.co.uk/

FYI: Feynman actually said in an interview: “I was in the cafeteria and some guy, fooling around, throws a plate in the air. As the plate went up in the air I saw it wobble, and I noticed the red medallion of Cornell on the plate going around. It was pretty obvious to me that the medallion went around faster than the wobbling. I had nothing to do, so I start figuring out the motion of the rotating plate. I discover that when the angle is very slight, the medallion rotates twice as fast as the wobble rate - two to one. It came out of a complicated equation! I went on to work out equations for wobbles. Then I thought about how the electron orbits start to move in relativity. Then there’s the Dirac equation in electrodynamics. And then quantum electrodynamics. And before I knew it....the whole business that I got the Nobel prize for came from that piddling around with the wobbling plate.” Although he was correct about QED, he was wrong about the rotating disk it appears. Oh well we can forgive him ... xD

I am 12 years old and I know that it’s wrong

I do not understand why we have to subtract the smaller circumference from the larger one, what does the difference between the two circumferences mean ? And why do we have to divide the difference between the two circumferences by the smaller circumference, what does the ratio mean ?

Precess. r^0/t^0=1 Velocity. r^1/t^1=v Acceleration. r^1/t^2=a a*v=Q = r^2/t^3 charge I = r^3/t^4 current O magnetism. r^3/t^5=O m mass. r^4/t^6=m Mass is a precess of current loops of charge Charge is unbalanced equllibrium of collapsing space time

What about the Energy calculations. Input VS output.

Is it not obvious that it has a 1/1 ratio.

this video was beyond amazing, the topic, the aesthetics, the editing, everything

After waking up from a lucid dream, I spun a penny and said, "the length of time this coin stays up is the length of that dream." The coin spun and spun and came to a stop, but it never fell down.

I think there's only one group of people. Show us the spinning disk

spin the damn thing already.!

Euler's disc on a particularly large and polished steel drum.

Disc sounds like car, not disappointed

Pause the video at 5:10 right when Matt is saying the O in, "Wobble."

my left ear hurts

This is exactly the problem that helped get Richard Feynman excited about physics again, and as he worked on this problem, it led him to consider "spin" and electron rotation properties, which led him ultimately, to the work for which he won the Nobel prize! See this video, starting at about 20 min -- www.dailymotion.com/video/x6ptg1x

"Some men aren't looking for anything logical, like mathematics. They can't be bought, bullied, reasoned or negotiated with. Some men just want to watch the disk spin down."

It is COSINE not caws 😂😂😂🤭🤭🤭

I just want to see it spin.

So simple. So good. Great video!

I see to remember reading in Feynman's books that he noticed this in spinning plates and it led him on to make some other significant discovery

Who else only focused on the coin and forgot the explanation by him on the left side?

i need to know the number of takes you took to get the timing right...

This type of of videos should GOOGLE Put in my recommendation..

Woow!!!! First time i use my both left - right side of brain.. Fabulous.

the Arrow is on the wrong side of disk. that's the bottom side of disk per included instructions. the smoothed edge is the bottom of disk and the edge you should start your spin on.

Awesome...

So as the angle decreases and the rate increases, does that also mean r slowly approaches R? I'm guessing it stops spinning *just before* they're equal because physics aren't necessarily as perfect as math.

I got this exact one, it freaks people out. Found mine here ===> amzn.to/2VszCRw

Uhhh, oh... ok. I think I got it now. On second thought..

I bought my cal 3 teacher one last semester. He was a good teacher

Freaking awesome Brother Man

I wish this guy was my high school math teacher! lol

This is sooo good!

breakdancing coins? gotta love it.

Nice audio channels usage.

Who else came here because you saw it on The Big Bang Theory?

Stupendously done

Was hoping to discover why spinning the disk on a concave surface makes it spin longer? Something to do with cycloids and least energy? And why is it called Euler's Disk?

7:46 perfection.

4:41 best timing ever

Amazing video

Stupid question. Is the plate that the disk spins on required for the effect to work or is it for another purpose?

what a beautiful sine wave made by that arrow

“Supersized mega version” Supermega

very very good !

Youre a fuckin asshole for stopping it repeatedly-_-

If you listen to the right speaker only... It's what I hear in class XD If anyone ever wanted to know what ADHD was like, bring them to this video and tell them to just put on the right speaker.

Wobble and spinning RICHARD FYNMEN ALSO DID SOMETHING SIMILAR

Oddly, weirdly hypnotic....

It would have been funny if you just interrupting it just before it finished.

If i only could give 2 "like".... Hell i would have given

Awesome timing 👍

I replayed it twice to watch both

Cool! What I wanna know is the frequency of rotation as a function of time of the disc.

Matt with that haircut reminds me of jim carrey ....(it's a compliment)

Gets the pictures going well with the sheet spinner.

The leftover can be tossed to other disks. At factorial!!!..

This is how sheets can hold other sheets at the brink of circular extension.

The arrow turns like the stopwatch

Hands down... Probably one of my favorite videos of all time.... Then again.... I say that every time

Not much going on here. He is just defining the angel. Not giving the differential equation describing the rate of the angular change and taking in the friction due to the surface between the disc and the mirror and also the drag due to the air resistans.

U forgot about friction but whatever

3:12 IT SOUNDS LIKE A TIME BOMB!

it's not "fitta", it's "theta"...

But you didn't tell why only Euler's disc spins for so long. How is it made?

Give me the frequency-time graph.

Yoooooo one of those eulers disks costs a whopping 120 bucks

Please define what you mean by wobbling (i.e what is one wobble)

great math

What does he mean by the left over/bonus bit? I dont get where that comes from or why we subtract

Jim Carrey?

that was impressive timing

Very nice

You made this in 2016. But it is my fave of 2017!...and this seems like the same math as two neutron stars colliding.

7:46 You can see how indeed wobble rate goes up as the angle decreases and spinning gets faster and then starts to slow down as it goes to 0 wobble rate becomes infinitely wobbly for an infinitely small time before it completely stops right lmao you can listen to it at the end idk what i'm typing but the formula is fantastic, I kind of wanna graph it over time to see what kind of thing comes out of it

Euler's di*k.

Shave that head bruh