What is a vector? - David Huynh

2,038,080 views ใƒป 2016-09-13

TED-Ed


์•„๋ž˜ ์˜๋ฌธ์ž๋ง‰์„ ๋”๋ธ”ํด๋ฆญํ•˜์‹œ๋ฉด ์˜์ƒ์ด ์žฌ์ƒ๋ฉ๋‹ˆ๋‹ค.

๋ฒˆ์—ญ: Ju Hye Lim ๊ฒ€ํ† : Katherine Cho
00:07
Physicists,
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๋ฌผ๋ฆฌํ•™์ž์™€
00:08
air traffic controllers,
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ํ•ญ๊ณต ๊ตํ†ต ๊ด€์ œ์‚ฌ
00:09
and video game creators
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๋น„๋””์˜ค ๊ฒŒ์ž„ ์ œ์ž‘์ž๋“ค์€
00:11
all have at least one thing in common:
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์ ์–ด๋„ ํ•œ ๊ฐ€์ง€ ๊ณตํ†ต์ ์„ ๊ฐ€์ง€๊ณ  ์žˆ์Šต๋‹ˆ๋‹ค.
00:14
vectors.
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๋ฒกํ„ฐ์ž…๋‹ˆ๋‹ค.
00:15
What exactly are they, and why do they matter?
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๋ฒกํ„ฐ๊ฐ€ ์ •ํ™•ํžˆ ๋ฌด์—‡์ด๊ณ  ์™œ ์ค‘์š”ํ• ๊นŒ์š”?
00:19
To answer, we first need to understand scalars.
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์ด ์งˆ๋ฌธ์— ๋‹ต์„ ํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ๋จผ์ € ์Šค์นผ๋ผ๊ฐ€ ๋ฌด์—‡์ธ์ง€ ์•Œ์•„์•ผ ํ•ฉ๋‹ˆ๋‹ค.
00:23
A scalar is a quantity with magnitude.
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์Šค์นผ๋ผ๋Š” ํฌ๊ธฐ๊ฐ€ ์žˆ๋Š” ๋ฌผ๋ฆฌ๋Ÿ‰์ž…๋‹ˆ๋‹ค.
00:26
It tells us how much of something there is.
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๋ฌด์–ธ๊ฐ€๊ฐ€ ์–ผ๋งˆ๋‚˜ ์žˆ๋Š”์ง€ ์•Œ๋ ค์ค๋‹ˆ๋‹ค.
00:29
The distance between you and a bench,
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์—ฌ๋Ÿฌ๋ถ„๊ณผ ๋ฒค์น˜ ์‚ฌ์ด์˜ ๊ฑฐ๋ฆฌ๋„
00:31
and the volume and temperature of the beverage in your cup
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์ปต์— ๋“  ์Œ๋ฃŒ์˜ ๋ถ€ํ”ผ์™€ ์˜จ๋„๋„
00:34
are all described by scalars.
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์Šค์นผ๋ผ๋กœ ๋‚˜ํƒ€๋ƒ…๋‹ˆ๋‹ค.
00:37
Vector quantities also have a magnitude plus an extra piece of information,
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๋ฒกํ„ฐ ๋ฌผ๋ฆฌ๋Ÿ‰์€ ํฌ๊ธฐ์—๋‹ค ์ถ”๊ฐ€์ ์ธ ์ •๋ณด๋ฅผ ํ•˜๋‚˜ ๋” ๊ฐ€์ง‘๋‹ˆ๋‹ค.
00:42
direction.
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๋ฐฉํ–ฅ์ด์ฃ .
00:44
To navigate to your bench,
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๋ฒค์น˜๋กœ ๊ฐ€๊ธฐ ์œ„ํ•ด์„œ๋Š”
00:45
you need to know how far away it is and in what direction,
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์–ผ๋งˆ๋‚˜ ๋ฉ€๋ฆฌ ์žˆ๋Š”์ง€์™€ ์–ด๋Š ๋ฐฉํ–ฅ์— ์žˆ๋Š”์ง€๋ฅผ ์•Œ์•„์•ผ ํ•ฉ๋‹ˆ๋‹ค.
00:49
not just the distance, but the displacement.
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๊ฑฐ๋ฆฌ๋งŒ์ด ์•„๋‹ˆ๋ผ ๋ณ€์œ„๋„ ํ•„์š”ํ•˜์ฃ .
00:53
What makes vectors special and useful in all sorts of fields
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๋ฒกํ„ฐ๊ฐ€ ๋‹ค์–‘ํ•œ ๋ถ„์•ผ์—์„œ ํŠน๋ณ„ํ•˜๊ณ  ์œ ์šฉํ•œ ์ด์œ ๋Š”
00:56
is that they don't change based on perspective
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์‹œ๊ฐ์— ๋”ฐ๋ผ ๋ณ€ํ•˜์ง€ ์•Š๊ณ 
00:59
but remain invariant to the coordinate system.
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์ขŒํ‘œ์— ๋ถˆ๋ณ€์ ์œผ๋กœ ๋‚จ์•„์žˆ๊ธฐ ๋•Œ๋ฌธ์ž…๋‹ˆ๋‹ค.
01:03
What does that mean?
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์ด๊ฒŒ ๋ฌด์Šจ ๋œป์ผ๊นŒ์š”?
01:04
Let's say you and a friend are moving your tent.
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์—ฌ๋Ÿฌ๋ถ„์ด ์นœ๊ตฌ์™€ ํ…ํŠธ๋ฅผ ์˜ฎ๊ธด๋‹ค๊ณ  ๊ฐ€์ •ํ•ด ๋ด…์‹œ๋‹ค.
01:07
You stand on opposite sides so you're facing in opposite directions.
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์„œ๋กœ ๋ฐ˜๋Œ€์ชฝ์— ์„œ์„œ ๋ฐ˜๋Œ€ ๋ฐฉํ–ฅ์„ ๋ฐ”๋ผ๋ณด๊ณ  ์žˆ๊ฒ ์ฃ .
01:11
Your friend moves two steps to the right and three steps forward
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์นœ๊ตฌ๋Š” ์˜ค๋ฅธ์ชฝ์œผ๋กœ ๋‘ ๊ฑธ์Œ, ์•ž์œผ๋กœ ์„ธ ๊ฑธ์Œ ๊ฐ€๊ณ 
01:15
while you move two steps to the left and three steps back.
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์—ฌ๋Ÿฌ๋ถ„์€ ์™ผ์ชฝ์œผ๋กœ ๋‘ ๊ฑธ์Œ, ๋’ค๋กœ ์„ธ ๊ฑธ์Œ ๊ฐ‘๋‹ˆ๋‹ค.
01:19
But even though it seems like you're moving differently,
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์„œ๋กœ ๋‹ค๋ฅด๊ฒŒ ์›€์ง์ด๊ณ  ์žˆ๋Š” ๊ฒƒ ๊ฐ™์ง€๋งŒ
01:22
you both end up moving the same distance in the same direction
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๊ฒฐ๊ตญ ๋‘˜ ๋‹ค ๊ฐ™์€ ๊ฑฐ๋ฆฌ๋ฅผ ๊ฐ™์€ ๋ฐฉํ–ฅ์œผ๋กœ ์›€์ง์ด๋Š” ๊ฒฐ๊ณผ๊ฐ€ ๋‚˜์˜ต๋‹ˆ๋‹ค.
01:25
following the same vector.
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๊ฐ™์€ ๋ฒกํ„ฐ๋ฅผ ๋”ฐ๋ผ์„œ์š”.
01:28
No matter which way you face,
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์–ด๋Š ๋ฐฉํ–ฅ์„ ๋ฐ”๋ผ๋ณด๊ณ  ์žˆ๋“ 
01:30
or what coordinate system you place over the camp ground,
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์บ ํ”„์žฅ์— ์–ด๋–ค ์ขŒํ‘œ๋ฅผ ๊ทธ๋ฆฌ๋“ 
01:33
the vector doesn't change.
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๋ฒกํ„ฐ๋Š” ๋ณ€ํ•˜์ง€ ์•Š์Šต๋‹ˆ๋‹ค.
01:35
Let's use the familiar Cartesian coordinate system
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x์ถ•๊ณผ y์ถ•์ด ์žˆ๋Š” ์šฐ๋ฆฌ์—๊ฒŒ ์ต์ˆ™ํ•œ
01:38
with its x and y axes.
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์ง๊ต ์ขŒํ‘œ๊ณ„๋ฅผ ์จ ๋ด…์‹œ๋‹ค.
01:40
We call these two directions our coordinate basis
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์šฐ๋ฆฌ๋Š” ์ด x์™€ y ๋‘ ๋ฐฉํ–ฅ์„ ์ขŒํ‘œ ๊ธฐ์ €๋ผ๊ณ  ๋ถ€๋ฆ…๋‹ˆ๋‹ค.
01:43
because they're used to describe everything we graph.
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์šฐ๋ฆฌ๊ฐ€ ๊ทธ๋ž˜ํ”„๋กœ ๊ทธ๋ฆฌ๋Š” ๋ชจ๋“  ๊ฒƒ์„ ๋‚˜ํƒ€๋‚ด๋Š” ๋ฐ ์“ฐ์ด๊ธฐ ๋•Œ๋ฌธ์ด์ฃ .
01:46
Let's say the tent starts at the origin and ends up over here at point B.
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ํ…ํŠธ๊ฐ€ ์›์ ์—์„œ ์ถœ๋ฐœํ•˜์—ฌ B์ ์œผ๋กœ ์ด๋™ํ•œ๋‹ค๊ณ  ๊ฐ€์ •ํ•ด ๋ด…์‹œ๋‹ค.
01:51
The straight arrow connecting the two points
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๋‘ ์ ์„ ์—ฐ๊ฒฐํ•˜๋Š” ์ง์„ ์ด
01:54
is the vector from the origin to B.
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์›์ ์—์„œ B๊นŒ์ง€์˜ ๋ฒกํ„ฐ์ž…๋‹ˆ๋‹ค.
01:56
When your friend thinks about where he has to move,
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์นœ๊ตฌ๊ฐ€ ์–ด๋””๋กœ ์›€์ง์—ฌ์•ผ ํ•˜๋Š”์ง€๋ฅผ
01:59
it can be written mathematically as 2x + 3y,
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์ˆ˜ํ•™์ ์œผ๋กœ 2x+3y๋กœ ๋‚˜ํƒ€๋‚ผ ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
02:03
or, like this, which is called an array.
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์•„๋‹ˆ๋ฉด ์ด๋ ‡๊ฒŒ ๋ฐฐ์—ด๋กœ ๋‚˜ํƒ€๋‚ผ ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
02:07
Since you're facing the other way,
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์—ฌ๋Ÿฌ๋ถ„์€ ๋‹ค๋ฅธ ๋ฐฉํ–ฅ์„ ๋ฐ”๋ผ๋ณด๊ณ  ์žˆ๊ธฐ์—
02:08
your coordinate basis points in opposite directions,
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์ขŒํ‘œ ๊ธฐ์ €์ ์ด ๋ฐ˜๋Œ€ ๋ฐฉํ–ฅ์ž…๋‹ˆ๋‹ค.
02:12
which we can call x prime and y prime,
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x ๋‹ค์‹œ์™€ y ๋‹ค์‹œ๋ผ๊ณ  ๋ถ€๋ฅผ ์ˆ˜ ์žˆ์ฃ .
02:15
and your movement can be written like this,
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์—ฌ๋Ÿฌ๋ถ„์˜ ์›€์ง์ž„์€ ์ด๋ ‡๊ฒŒ ๋‚˜ํƒ€๋‚ด๊ฑฐ๋‚˜
02:18
or with this array.
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์ด๋Ÿฐ ๋ฐฐ์—ด๋กœ ๋‚˜ํƒ€๋‚ผ ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
02:21
If we look at the two arrays, they're clearly not the same,
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๋‘ ๋ฐฐ์—ด์„ ๋ณด๋ฉด, ๋ณด์‹œ๋‹ค์‹œํ”ผ ์„œ๋กœ ๋‹ค๋ฆ…๋‹ˆ๋‹ค.
02:25
but an array alone doesn't completely describe a vector.
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ํ•˜์ง€๋งŒ ๋ฐฐ์—ด ํ•˜๋‚˜๊ฐ€ ๋ฒกํ„ฐ๋ฅผ ์™„์ „ํžˆ ํ‘œํ˜„ํ•˜์ง€๋Š” ๋ชปํ•ฉ๋‹ˆ๋‹ค.
02:29
Each needs a basis to give it context,
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๊ฐ ๋ฐฐ์—ด์€ ๋งฅ๋ฝ์„ ๊ฐ–๊ธฐ ์œ„ํ•ด์„œ ๊ธฐ์ €๊ฐ€ ํ•„์š”ํ•ฉ๋‹ˆ๋‹ค.
02:32
and when we properly assign them,
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๊ธฐ์ €๋ฅผ ์˜ฌ๋ฐ”๋ฅด๊ฒŒ ๋ถ€์—ฌํ•˜๋ฉด
02:34
we see that they are in fact describing the same vector.
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๋‘ ๋ฐฐ์—ด์ด ๊ฐ™์€ ๋ฒกํ„ฐ๋ฅผ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
02:38
You can think of elements in the array as individual letters.
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๋ฐฐ์—ด์˜ ๊ฐ ๋ณ€์ˆ˜๋“ค์„ ๊ฐœ๋ณ„์ ์ธ ๊ธ€์ž๋ผ๊ณ  ์ƒ๊ฐํ•˜๋ฉด ๋ฉ๋‹ˆ๋‹ค.
02:41
Just as a sequence of letters only becomes a word
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๊ธ€์ž์˜ ์ˆœ์—ด์ด ํŠน์ • ์–ธ์˜ ๋งฅ๋ฝ ์•ˆ์—์„œ๋งŒ
02:44
in the context of a particular language,
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๋‹จ์–ด๊ฐ€ ๋˜๋Š” ๊ฒƒ์ฒ˜๋Ÿผ,
02:47
an array acquires meaning as a vector when assigned a coordinate basis.
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๋ฐฐ์—ด์€ ์ขŒํ‘œ ๊ธฐ์ €๊ฐ€ ์ฃผ์–ด์งˆ ๋•Œ ๋ฒกํ„ฐ๋กœ์„œ์˜ ์˜๋ฏธ๋ฅผ ๊ฐ–๊ฒŒ ๋ฉ๋‹ˆ๋‹ค.
02:52
And just as different words in two languages can convey the same idea,
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๋‘ ์–ธ์–ด์˜ ๋‹ค๋ฅธ ๋‹จ์–ด๋“ค์ด ๊ฐ™์€ ๊ฐœ๋…์„ ์˜๋ฏธํ•  ์ˆ˜ ์žˆ๋Š” ๊ฒƒ์ฒ˜๋Ÿผ
02:57
different representations from two bases can describe the same vector.
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๋‘ ๊ธฐ์ €์˜ ๋‹ค๋ฅธ ์‹๋„ ๊ฐ™์€ ๋ฒกํ„ฐ๋ฅผ ๋‚˜ํƒ€๋‚ผ ์ˆ˜ ์žˆ์Šต๋‹ˆ๋‹ค.
03:01
The vector is the essence of what's being communicated,
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๋ฒกํ„ฐ๋Š” ์†Œํ†ต๋˜๋Š” ๋‚ด์šฉ์˜ ๋ณธ์งˆ์ด๋ฉฐ
03:05
regardless of the language used to describe it.
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์ด๋ฅผ ํ‘œํ˜„ํ•˜๊ธฐ ์œ„ํ•ด ์‚ฌ์šฉํ•˜๋Š” ์–ธ์–ด์™€ ์ƒ๊ด€ ์—†์Šต๋‹ˆ๋‹ค.
03:08
It turns out that scalars also share this coordinate invariance property.
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์Šค์นผ๋ผ๋„ ์ขŒํ‘œ ๋ถˆ๋ณ€์„ฑ์„ ์ง€๋‹ˆ๊ณ  ์žˆ์Šต๋‹ˆ๋‹ค.
03:12
In fact, all quantities with this property are members of a group called tensors.
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์‚ฌ์‹ค, ์ด ์„ฑ์งˆ์„ ๊ฐ€์ง„ ๋ชจ๋“  ๋ฌผ๋ฆฌ๋Ÿ‰์€ ํ…์„œ๋ผ๋Š” ์ง‘๋‹จ์— ํฌํ•จ๋ฉ๋‹ˆ๋‹ค.
03:18
Various types of tensors contain different amounts of information.
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๋‹ค์–‘ํ•œ ์ข…๋ฅ˜์˜ ํ…์„œ๋Š” ๋‹ค๋ฅธ ์–‘์˜ ์ •๋ณด๋ฅผ ๊ฐ–๊ณ  ์žˆ์Šต๋‹ˆ๋‹ค.
03:22
Does that mean there's something that can convey more information than vectors?
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๊ทธ๋ ‡๋‹ค๋ฉด ๋ฒกํ„ฐ๋ณด๋‹ค ๋” ๋งŽ์€ ์ •๋ณด๋ฅผ ์ „๋‹ฌํ•  ์ˆ˜ ์žˆ๋Š” ๊ฒŒ ์žˆ๋Š” ๊ฑธ๊นŒ์š”?
03:26
Absolutely.
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๋ฌผ๋ก ์ž…๋‹ˆ๋‹ค.
03:28
Say you're designing a video game,
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๋น„๋””์˜ค ๊ฒŒ์ž„์„ ์„ค๊ณ„ํ•˜๋Š”๋ฐ
03:29
and you want to realistically model how water behaves.
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๋ฌผ์ด ์›€์ง์ด๋Š” ๋ชจ์Šต์„ ํ˜„์‹ค์ ์œผ๋กœ ๋‹ด์œผ๋ ค ํ•œ๋‹ค๊ณ  ๊ฐ€์ •ํ•ด ๋ด…์‹œ๋‹ค.
03:33
Even if you have forces acting in the same direction
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๊ฐ™์€ ๋ฐฉํ–ฅ๊ณผ ๊ทœ๋ชจ๋กœ ์ž‘์šฉํ•˜๋Š”
03:36
with the same magnitude,
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ํž˜์ด ์žˆ๋”๋ผ๋„
03:38
depending on how they're oriented, you might see waves or whirls.
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์–ด๋–ป๊ฒŒ ๋ชจ์—ฌ์žˆ๋Š”์ง€์— ๋”ฐ๋ผ ํŒŒ๋„๋‚˜ ์†Œ์šฉ๋Œ์ด๊ฐ€ ์ƒ๊น๋‹ˆ๋‹ค.
03:42
When force, a vector, is combined with another vector that provides orientation,
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๋ฒกํ„ฐ์ธ ํž˜์ด ๋ฐฉํ–ฅ์„ ๋ถ€์—ฌํ•˜๋Š” ๋‹ค๋ฅธ ๋ฒกํ„ฐ์™€ ๊ฒฐํ•ฉ๋˜๋ฉด
03:47
we have the physical quantity called stress,
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์‘๋ ฅ์ด๋ผ๋Š” ๋ฌผ๋ฆฌ๋Ÿ‰์ด ์ƒ๊ธฐ๋ฉฐ, 2์ฐจ ํ…์„œ์˜ ์‚ฌ๋ก€์ธ
03:50
which is an example of a second order tensor.
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์ด๋Š” 2์ฐจ ํ…์„œ์˜ ์˜ˆ์ž…๋‹ˆ๋‹ค.
03:54
These tensors are also used outside of video games for all sorts of purposes,
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์ด ํ…์„œ๋“ค์€ ๋น„๋””์˜ค ๊ฒŒ์ž„ ์™ธ์—๋„ ๋‹ค์–‘ํ•œ ์šฉ๋„๋กœ ์“ฐ์ž…๋‹ˆ๋‹ค.
03:59
including scientific simulations,
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๊ณผํ•™ ๋ชจ์˜์‹คํ—˜์ด๋‚˜
04:01
car designs,
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์ž๋™์ฐจ ๋””์ž์ธ
04:02
and brain imaging.
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๋‡Œ ์˜์ƒ ์ดฌ์˜๊ฐ™์€ ๊ณณ์—์š”.
04:04
Scalars, vectors, and the tensor family present us with a relatively simple way
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์Šค์นผ๋ผ์™€, ๋ฒกํ„ฐ, ๊ทธ๋ฆฌ๊ณ  ํ…์„œ ๊ฐ€์กฑ์€ ๋ณต์žกํ•œ ๊ฐœ๋…๊ณผ ์ƒํ˜ธ์ž‘์šฉ์„
04:09
of making sense of complex ideas and interactions,
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์ดํ•ดํ•˜๋Š” ๋ฐ์— ๋น„๊ต์  ๊ฐ„๋‹จํ•œ ๋ฐฉ๋ฒ•์„ ์ œ๊ณตํ•ด ์ค๋‹ˆ๋‹ค.
04:12
and as such, they're a prime example of the elegance, beauty,
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๊ทธ๋ ‡๊ธฐ ๋•Œ๋ฌธ์— ์ˆ˜ํ•™์˜ ์šฐ์•„ํ•จ๊ณผ ์•„๋ฆ„๋‹ค์›€
04:16
and fundamental usefulness of mathematics.
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๊ทธ๋ฆฌ๊ณ  ๊ทผ๋ณธ์ ์ธ ์œ ์šฉํ•จ์˜ ์•„์ฃผ ์ข‹์€ ์˜ˆ๊ฐ€ ๋ฉ๋‹ˆ๋‹ค.

Original video on YouTube.com
์ด ์›น์‚ฌ์ดํŠธ ์ •๋ณด

์ด ์‚ฌ์ดํŠธ๋Š” ์˜์–ด ํ•™์Šต์— ์œ ์šฉํ•œ YouTube ๋™์˜์ƒ์„ ์†Œ๊ฐœํ•ฉ๋‹ˆ๋‹ค. ์ „ ์„ธ๊ณ„ ์ตœ๊ณ ์˜ ์„ ์ƒ๋‹˜๋“ค์ด ๊ฐ€๋ฅด์น˜๋Š” ์˜์–ด ์ˆ˜์—…์„ ๋ณด๊ฒŒ ๋  ๊ฒƒ์ž…๋‹ˆ๋‹ค. ๊ฐ ๋™์˜์ƒ ํŽ˜์ด์ง€์— ํ‘œ์‹œ๋˜๋Š” ์˜์–ด ์ž๋ง‰์„ ๋”๋ธ” ํด๋ฆญํ•˜๋ฉด ๊ทธ๊ณณ์—์„œ ๋™์˜์ƒ์ด ์žฌ์ƒ๋ฉ๋‹ˆ๋‹ค. ๋น„๋””์˜ค ์žฌ์ƒ์— ๋งž์ถฐ ์ž๋ง‰์ด ์Šคํฌ๋กค๋ฉ๋‹ˆ๋‹ค. ์˜๊ฒฌ์ด๋‚˜ ์š”์ฒญ์ด ์žˆ๋Š” ๊ฒฝ์šฐ ์ด ๋ฌธ์˜ ์–‘์‹์„ ์‚ฌ์šฉํ•˜์—ฌ ๋ฌธ์˜ํ•˜์‹ญ์‹œ์˜ค.

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