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  • So you're me, and you're in math class.

  • And your teacher's ranting on and on

  • about this article about whether

  • algebra should be taught in school

  • as if he doesn't realize that what he's teaching

  • isn't even algebra

  • which could have been interesting

  • but how to manipulate symbols

  • and some special cases of elementary algebra

  • which isn't.

  • And so, instead of learning about

  • self-consistent systems and logical thought,

  • you spent all week memorizing

  • how to graph parabolas.

  • News flash: No one cares about parabolas.

  • Which is why half the class is

  • playing Angry Birds under their desks.

  • But, since you don't have a smart phone yet,

  • you have to resort to a more noble

  • and outdated form of boredom relief

  • that is, doodling.

  • And you've invented a game of your own.

  • A doodle game that connects the dots

  • in ways your math curriculum never will

  • except instead of connecting to the closest dots

  • to discover the mysterious hidden picture

  • you've got this precise method of skipping over

  • some number of dots and connecting them that way.

  • In the past you've characterized how this works

  • if your dots are arranged in a circlesay 11 dots

  • and connect one to the dot four dots over,

  • you get these awesome stars.

  • And you can either draw the lines

  • in the order of the dots,

  • or you can just keep going around and

  • maybe it will hit all the dots, or maybe it won't,

  • depending on how many dots are in your circle,

  • and how many dots you skip.

  • But then there are other shapes.

  • Circles are good friends with sine waves.

  • And sine waves are good friends with square waves.

  • And let's admit it, that's pretty cool looking.

  • In fact, just two simple straight lines of dots

  • connecting the dots from one line to the other

  • in order somehow gives you

  • this awesome woven curve shape.

  • Another student is asking the teacher when he's ever

  • going to need to know how to graph a parabola

  • even as he hides his multi-million dollar enterprise

  • of a parabola graphing game under his desk.

  • If your teacher thought about it,

  • he would probably think shooting birds at things

  • is a great reason to learn about parabolas

  • because he's come to understand that

  • education is about money and prestige and

  • not about becoming a better human able to do great things.

  • You yourself haven't done anything really great yet

  • but you figure the path to your future greatness

  • lies more in inventing awesome new connect-the-dot arrangements

  • than in graphing parabolas or shooting birds at things.

  • And that's when you begin to worry.

  • What if this cool liney curvey thing you drew

  • approximates a parabola?

  • As if your teacher doesn't realize

  • everyone has their phones under their desks,

  • but he's underpaid and overworked and

  • his whole word runs on plausible deniability,

  • so he shouts state-mandated, pass the test,

  • teach-to-the-middle nonsense at students

  • who are not at all fooled

  • by his false enthusiasm or false mathematics and

  • he pretends he's teaching algebra and

  • the students pretend to be taught algebra and

  • everyone else involved in the system

  • is too invested to do anything

  • but pretend to believe them both.

  • You think maybe it's a hyperbola,

  • which is similar to the parabola

  • in that they are both conic sections.

  • A hyperbola is a nice vertical slice of cone,

  • the cone itself being just like a line swirled around in a circle,

  • which is why the cone is like two cones radiating both ways;

  • the lovely hyperbola insecting both parts.

  • Two perfect curves, looking disconnected when seen alone

  • but sharing their common conic heritage.

  • While the boring old parabola is a slice taken at an angle

  • completely meant to miss the top part of the cone and

  • to miss wrapping around the bottom like an ellipse would.

  • And it's such a special, specific case of conic section

  • that all parabolas are exactly the same,

  • just bigger or smaller or moved around.

  • Your teacher could just as well hand you parabolas already drawn

  • and have you draw coordinate grids on parabolas

  • rather than parabolas on coordinate grids.

  • And it's stupid, and you hate it,

  • and you don't wanna learn to graph them,

  • even if it means not making a billion dollars

  • from a game about shooting birds at things.

  • Meanwhile anyone who actually learns how to think mathematically

  • can then learn to graph a parabola or anything else

  • they need in like five minutes.

  • But teaching how to think is an individualized process

  • that gives power and responsibility to individuals

  • while teaching what to think can be done

  • with one-size-fits-all bullet points and check-boxes

  • and our culture of excuses demands that we do the latter,

  • keeping ourselves placated in the comforting structure

  • of tautology and clear expectations.

  • Algebra has become a check-box subject and

  • mathematics weeps alone in the top of the ivory tower prison

  • to which she has been condemned.

  • But you're not interested in check-boxes;

  • you're interested in dots, and lines that connect them.

  • Or maybe you could connect them with semicircles,

  • to give visual structure to lines that would otherwise overlap.

  • Or you could say one dot is the center of a circle and

  • another defines a radius and draw the entire circle

  • and do things that way.

  • You could make rules about how every dot

  • is the center of a circle with its neighbor being the radius,

  • or say one dot stays the center of all circles,

  • and all of the others define radii.

  • But then you just get concentric circles,

  • which I suppose should have been obvious.

  • But what if you did it the other way around and

  • said one dot always stays on the circle and

  • all the other dots are centers, like this.

  • Looks more promising.

  • So you try putting all the dots in a circle and

  • using them as circle centers and

  • choose just one dot for the circles to go through and

  • you get this awesome shape that looks kind of like a heart.

  • So let's call it, oh I don't know, a cardioid.

  • Which happens to be the same curve that you get

  • when parallel lines like rays of light reflect off a circle

  • the same heart of sunshine in a cup.

  • Or maybe instead of circle centers

  • you could have points all on the curve of a circle,

  • which means you need three points to define a circle,

  • maybe just a point and its two closest neighbors to start with.

  • And of course, any collection of circles is two-colorable,

  • which means you can contrast light and dark colors

  • for a classy color scheme.

  • Or maybe you could throw down some random points

  • to make all possible circles.

  • Only that would be a lot of circles,

  • so you choose just ones you like.

  • And then, against your will, you begin to wonder

  • how many points it takes to define the boring old parabola.

  • Because parabolas are actually a lot like circles in that

  • both are like extreme ellipses,

  • because a circle is like taking one focus of an ellipse

  • and putting the other focus zero distance away.

  • And a parabola is like an ellipse where

  • one focus is infinity distance away.

  • Which is why everyone lies to you and says

  • throwing balls or shooting birds is all about parabolas

  • when really it's about ellipses

  • because the earth is a sphere and

  • gravity doesn't actually go straight down.

  • And the other focus of the elliptical orbit of

  • your thrown object of choice may be very far away,

  • but very far away is a great bit closer than infinity.

  • So let's not fool ourselves.

  • You can't look at everything that seems kind of parabolic

  • and call it a parabola.

  • Sure, if you connect two dots with a hanging string or chain,

  • it looks parabolic, and so do structurally strong arches,

  • but they're actually catenary arches and

  • maybe you can't tell by sight,

  • but if you're an architect you'd better know the difference.

  • Though caternarys are quite related to parabolas,

  • you get them by rolling around a parabola

  • and tracing the focus

  • which makes them a cousin of the ellipse and

  • even a hyperbola is like an ellipse that got turned inside out

  • or whose focus went through infinity and

  • came out the other side or something.

  • And of course parabolas and hyperbolas and ellipses

  • are all conic sections which mean

  • they all come from a line that got spun around.

  • And a line is just what happens

  • when a couple dots get connected.

  • Or maybe what happens when your circle is so big that,

  • like the extreme ellipse that becomes a parabola,

  • the extreme circle is broken at infinity and

  • becomes a line before getting larger than infinitely big

  • which brings it back to the other side.

  • This linear circle, the infinite in-between.

  • Or maybe a line is what happens

  • when you roll around a circle and trace the focus.

  • Or rather the 2 foci, which are zero distance apart, in ellipse terms.

  • Which makes you wonder what you get

  • when you roll around an ellipse and trace the foci.

  • In fact, there's lots of great shapes

  • you can get by rolling around shapes on other shapes,

  • like if you roll a circle around a circle and trace the focus,

  • you get just another circle.

  • But, if you trace a point on the edge,

  • you get our awesome friend the cardioid again.

  • So now it's related to circles in three ways ,

  • which means it's a close cousin of the ellipse

  • and a second cousin to the infinite ellipse or, parabola.

  • Except, not just that, if you take a parabola and

  • invert it around the unit circle, reversing inside and outside,

  • one half becomes two, one hundred becomes a hundredth,

  • one stays one, infinity becomes zero,

  • you get once again, the cardioid.

  • The cardioid is the anti-parabola which is good

  • because parabolas make you sad but you heart cardioids.

  • And of course, any time you want to

  • connect two dots on a piece of paper,

  • instead of drawing the line you could fold the line.

  • Here's the thing about connecting dots.

  • You can have all the steps laid out for you,

  • taking whatever next step is easiest and closest

  • and be sure of what you're getting the whole time.

  • This way is safe and comfortable.

  • Or, you can try new ways of connecting dots

  • and not know what you're going to get.

  • Maybe it will be something great, maybe it will fail.

  • And when it fails it will be your fault.

  • You can't blame anyone else, not mathematics

  • or the system or the check-boxes.

  • But if I am to have faults I would rather they be my own.

So you're me, and you're in math class.

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B1 中級

算数の授業での落書き点をつなぐ (Doodling in Math Class: Connecting Dots)

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    林宜悉 に公開 2021 年 01 月 14 日
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