Math Jokes Explained - Numberphile Numberphile English English (auto-generated)

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Science & Technology 2.7M views 42K likes 1.6K dislikes 20 May 2013

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[MICROPHONE FEEDBACK] -Is this thing on? [TAPPING] [COUGHING]

is this thing on

-So a man walks into a bar.

so man walks into a bar he asks for ten

He asks for 10 times more drinks than everyone else.

times more drinks than everyone else the

The barman says, now, that is an order of magnitude.

barman says now that is an order of

MATT PARKER: Actually quite a good joke, because order of

magnitude actually quite a good joke

magnitude is how big a number is.

because order of magnitude is how big a

The speed of light is 3 times 10 to the 8 meters per second,

number is a speed of light is three times ten to the eighth meters per

and that's the order of magnitude.

second and that's the order of magnitude

It's 3 with eight 0's after it.

it's three with eight zeros after it and

And something like a kilometer is 10 to the 3 meters. So light in one second goes five orders of magnitude

something like a kilometer is ten to the three meters so light in one second goes five orders of magnitude further than a

further than a kilometer. And so when he says, I want 10 times as many drinks, he's

kilometer and so when he says I want ten times as many drinks he's actually

actually ordering one order of magnitude more than anyone

ordering one order of magnitude more

else, which is, of course, an order of magnitude.

than anyone else which is of course an order of magnitude so an infinite number

-So an infinite number of mathematicians walk into a bar.

of mathematicians walk into a bar the

The first one, he orders a pint.

first one he orders a pint the second

The second one, half a pint, then a

one half a pint then a quarter then an

quarter, then an eighth.

eighth eventually the barman hands over

Eventually, the barman hands over two pints and says, you

two pints and says you mathematicians

mathematicians. You just don't know your limits.

you just don't know your limits okay so

MATT PARKER: OK, so if you start with 1, and then you add

if you start with one and then you add a

1/2, and then you add 1/4, and then you add 1/8, and each

half and then you add a quarter and then you add an eighth and each time you're

time you're getting smaller and smaller, what we're

getting smaller and smaller what we're

actually doing is we're summing all

actually doing is we're summing all the

the 1/2 to the n's--

1 over 2 to the ends some end and we

some n. And we start with n equals 0, and we go all the way up to a

start with n equals 0 and we go all the

correctly drawn infinity sign.

way up to a correctly drawn infinity

And if you carry this on infinitely, its limit equals

sign and if you carry this on infinitely it's limit equals 2 which is why the

2, which is why the barman gave them two pints.

barman gave them two pints and he said

And he said, you don't know your limits.

you don't know your limits because

Because that's the limit.

that's a limit so why is six Afraid of

-So why is 6 afraid of 7?

Because 7 ate 9!

because seven eight nine not strictly a

MATT PARKER: Not strictly a math joke, but OK.

math joke but okay the thing here is

The thing here is that numbers appear in order.

that numbers appear in order they go one

They go 1, 2, 3, 4, 5, 6, 7, 8, 9.

two three four five six seven eight nine

Why is 6 scared of 7?

why is six scared of seven when you say

Well, when you say 7, 8, 9, the word "eight" in English

seven eight nine the word eight in

sounds a bit like the word "ate." So it

English sounds a bit like the word eight

sounds like 7 ate 9.

so it sounds like seven eight nine so

So eight is, in this case, a word.

eight is in this case a word and seven

And 7 then eats-- I don't know.

then eats I don't know it's I mean I

I mean, I personally would say that 7 is a 6 offender, but

personally would say that seven

I'm not the one doing the jokes here, am I?

is a six offender but I'm the one doing the jerks here am i how do you make

-How do you make seven even? Remove the S!

seven even remove the yes that was

MATT PARKER: I was promised number jokes, but I guess

promised number jokes but I guess

another English one is fine.

another English one is fine so the

So the number 7-- if you write it out in this language called English, which

number seven if you write it out in this

you may have heard of, you spell it "seven." And then if

language called English which you may have heard of you spell it seven and

you remove the S, you're left with the English word "even."

then if you remove the S you're left with the English word even no actual

No actual math's involved.

maths involved two cats are standing on

-Two cats are standing on a roof. Which one falls off first?

a roof which one falls off first the one

The one with the smaller mu.

with the smaller Mew

MATT PARKER: OK, bear with me here.

okay bear with me here I'm gonna

I'm going to represent the roof like this.

represent the roof like this the front

The front door and chimney are optional.

door and chimney are optional and then

And then I'm going to approximate

I'm gonna approximate the cat as a

the cat as a rectangle. Gravity is forcing the cat directly down.

rectangle gravity is forcing the cat directly down but of course it can't go

But of course, it can't go straight down because it's on

straight down because it's on a sloped

a sloped roof. And so you're going to split this into a normal vector,

roof and so you're gonna split this into a normal vector which comes off this way

which comes off this way, and then the vector going down the roof.

and then the vector going down the roof

What stops it from falling off the roof is friction. And friction will be a force coming back this way.

what stops it from falling off the roof is friction and friction will be a force coming back this way and friction is

And friction is proportional to how hard the box is being

proportional to how hard the box is

pressed down into the roof.

being pressed down into the roof and so

And so we have the coefficient of friction, which is the

we have the coefficient of friction

Greek letter mu, times whatever that normal force is.

which is the Greek letter mu times whatever that normal force is and so the

And so the bigger the coefficient of friction, the

bigger the coefficient of friction the

less likely it is to fall off.

less likely it is to fall off and if

And if there were two boxes, the one with the smaller

there were two boxes the one with the

coefficient of friction would fall off first.

smaller coefficient of friction would

And that is the Greek letter mu, which, if we're talking

fall off first and that is the Greek letter mu which if we're talking about

about cats, the cats make the sound meow.

cats the cats make the sound meow what

-What did the number 0 say to the number 8?

did the number zero say to the number

eight nice belt

MATT PARKER: OK, I guess so. So 0 looks a bit like this.

all right okay I guess so so zero looks a bit like this and if you imagine

And if you imagine putting a belt around 0 and then

putting a belt around zero and then

tightening it, it would squeeze the middle

tightening it it would squeeze the

of 0 in like that.

middle of zero in like like that and if

And if you tighten it enough, it would pinch off and

you tighten it enough it would pinch off

would form an 8.

and would form an eighth and so an

And so an 8 is a bit like a 0 wearing a belt.

eighth is a bit like a zero wearing a

Why it is a nice belt, I'm not sure.

belt why it is a nice belt I'm not sure

[MOSQUITO BUZZING]

-What do you get if you cross a mosquito

what do you get if you cross a mosquito

with a mountain climber?

with a mountain-climber

nothing you can't cross a vector and a

You can't cross a vector and a scalar.

scalar okay there's a lot going on here

MATT PARKER: Ok, there's a lot going on here. We'll start with what we mean by cross.

we'll start with what we mean by cross

And it's a way of saying multiply.

and it's a way of saying multiply when

When you multiply numbers together, it's easy.

you multiply numbers together it's easy

There's one thing you do.

there's one thing you do you multiply

You multiply one by the other.

one by the other when you multiply

When you multiply vectors, it gets a bit more complicated.

vectors it gets a bit more complicated

So let's say I've got one vector u, which has ux

so let's say I've got one vector U which

component, uy component, and uz component,

has UX component u Y component and used

because it's in 3D.

edge component because it's in 3d and

And then I've got another vector I'm going to call v. So

then I've got another vector

I've got vx component, vy component, vz component.

I'm gonna call V so I've got V X component V Y component the Z component

And then I want to multiply these two vectors.

and then I want to multiply these two

And there's more than one way to do that.

vectors and there's more than one way to

You can dot multiply, which gives you a scalar, which is

do that you can dot multiply which gives

just a normal number, out as an answer.

you a scalar it's just a normal number

Or you can cross multiply--

out as an answer or you can cross

using our traditional cross multiply symbol--

multiply using a traditional cross

which gives you out another vector.

multiply symbol which gives you our another vector now cross multiplying is

Now, cross multiplying is a little bit complicated.

a little bit complicated kay let's do

OK, let's do the first one. So it's uy normal multiply vz minus uz normal multiply vy. Then the next component-- and you keep going.

the first one so it's you y normal multiply V Z minus u Z normal multiply V Y then the next component you

And you get three new components out this way.

get three new components up this way the

The trouble is, you can only cross multiply vectors.

trouble is you can only cross multiply

You can't do the same thing for normal numbers, or

vectors you can't do the same thing for

scalars, as we call them.

normal numbers or scalars as we call

And someone who climbs the mountain is scaling it.

them and someone who climbs a mountain is scaling it so I guess you could call

So I guess you could call him a scaler. And a mosquito--

him a scalar and a mosquito and we're

we're going right outside maths here-- a mosquito can

going right outside maths here a

transmit diseases, which in biology, you would call a

mosquito can transmit diseases which in

vector as a way of transmitting diseases.

biology you would call a vector as a way of transmitting diseases and so you

And so you can't do a cross multiplication between a

can't do a cross multiplication between

vector and a scaler.

a vector and a scalar and so that's

And so that's the joke.

that's the joke did you hear the one

-Did you hear the one about the constipated mathematician?

about the constipated mathematician

He worked it out with a pencil.

he worked it out with a pencil

MATT PARKER: No.

ah

We're aware that there are other maths

we're aware that there are other masked

jokes we've not covered.

jokes who have not covered we're also

We're also aware that some of you have discovered the

aware that some of you have discovered

comments section underneath YouTube videos.

the comment section underneath YouTube

So if you have your own maths joke you'd like to contribute,

videos so if you have your own mask joke you'd like to contribute I mean it's

we'll not stop you.

like we may I'll stop you it's

It's definitely going to happen.

definitely going to happen and we will

And we will endeavor, if we get enough interesting ones,

endeavor if we get enough interesting

to explain the maths behind more maths jokes.

ones to explain the mass behind more

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