Would you weigh less in an elevator? - Carol Hedden

332,935 views ใƒป 2012-11-19

TED-Ed


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

00:00
Transcriber: tom carter Reviewer: Bedirhan Cinar
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๋ฒˆ์—ญ: Gemma Lee ๊ฒ€ํ† : K Bang
00:15
You step into an elevator.
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ์— ์˜ฌ๋ผํƒ‘๋‹ˆ๋‹ค.
00:17
It starts going down, fast.
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๋Š” ๋น ๋ฅธ ์†๋„๋กœ ๋‚ด๋ ค๊ฐ‘๋‹ˆ๋‹ค
00:19
What would happen if you jumped right when it started going down?
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๋งŒ์•ฝ ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ๋‚ด๋ ค๊ฐ€๊ธฐ ์‹œ์ž‘ํ•˜๋Š” ์ˆœ๊ฐ„ ์ ํ”„๋ฅผ ํ•œ๋‹ค๋ฉด ๋ฌด์Šจ ์ผ์ด ์ƒ๊ธธ๊นŒ์š”?
00:25
Would the ceiling hit your head? Ouch!
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์ฒœ์ •์— ๋จธ๋ฆฌ๋ฅผ ๋ฐ•๋Š”๊ฑธ๊นŒ์š”? ์•„์•ผ!
00:28
Do you stay suspended in the air while the elevator plummets down?
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ๋‚ด๋ ค๊ฐ€๋Š” ๋™์•ˆ ์—ฌ๋Ÿฌ๋ถ„์€ ๊ณต์ค‘์— ๋– ์žˆ๋Š” ๊ฑธ๊นŒ์š”?
00:32
Let's examine the elevator problem one step at a time.
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ ๋ฌธ์ œ๋ฅผ ํ•œ ๋ฒˆ์— ํ•˜๋‚˜์”ฉ ์‚ดํŽด๋ณด์ฃ .
00:37
First, consider a scale.
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๋จผ์ €, ์ €์šธ์„ ์ƒ๊ฐํ•ด๋ณด์„ธ์š”.
00:41
You know, the kind of scale you weigh yourself on.
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๋ชธ๋ฌด๊ฒŒ๋ฅผ ์žด ๋•Œ ์“ฐ๋Š” ์ €์šธ์ด์š”.
00:44
When you step on a scale to weigh yourself,
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๋ชธ๋ฌด๊ฒŒ๋ฅผ ์žฌ๋ ค๊ณ  ์ €์šธ์— ์˜ฌ๋ผ์„ค ๋•Œ
00:47
there are two forces involved.
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๊ฑฐ๊ธฐ์—” ๋‘ ํž˜์ด ์ž‘์šฉํ•ฉ๋‹ˆ๋‹ค.
00:49
One, gravity pulls you down.
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์ฒซ์งธ๋Š” ์ค‘๋ ฅ์ด ์—ฌ๋Ÿฌ๋ถ„์„ ์žก์•„๋‹น๊ธฐ์ฃ .
00:52
Two, the scale pushes you up.
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๋‘˜์งธ๋Š” ์ €์šธ์ด ์—ฌ๋Ÿฌ๋ถ„์„ ๋ฐ€์–ด์˜ฌ๋ ค์š”.
00:55
What? You didn't know a scale could push?
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๋ญ๋ผ๊ตฌ์š”? ์ €์šธ์ด ๋ฐ€์–ด์˜ฌ๋ฆฌ๋Š” ๊ฑธ ๋ชฐ๋ž๋‹ค๊ตฌ์š”?
00:58
Of course it can! If it didn't push up on you, you would go crashing through the floor.
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๋‹น์—ฐํžˆ ๋ฐ€์–ด์˜ฌ๋ฆด ์ˆ˜ ์žˆ์–ด์š”! ์ €์šธ์ด ๋ฐ€์–ด์˜ฌ๋ฆฌ์ง€ ์•Š์œผ๋ฉด ์—ฌ๋Ÿฌ๋ถ„์€ ๋ฐ”๋‹ฅ์„ ๊ฟฐ๋šซ๊ณ  ๋•…๋ฐ”๋‹ฅ์œผ๋กœ ์ฒ˜๋ฐ•ํž๊ฑฐ์—์š”.
01:03
This upward push is called the normal force and yes, it is normally there.
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์œ„๋กœ ๋ฐ€์–ด์˜ฌ๋ฆฌ๋Š” ํž˜์„ ์ˆ˜์งํ•ญ๋ ฅ์ด๋ผ๊ณ  ๋ถ€๋ฅด๊ณ , ์˜ˆ, ์–ด๋””์—๋‚˜ ์กด์žฌํ•˜๋Š” ํž˜์ž…๋‹ˆ๋‹ค.
01:10
Since you're just standing there on the scale, you're not moving.
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์—ฌ๋Ÿฌ๋ถ„์ด ์ €์šธ ์œ„์— ๊ฐ€๋งŒํžˆ ์„œ ์žˆ์œผ๋ฉด, ์›€์ง์ด์ง€ ์•Š๊ธฐ ๋•Œ๋ฌธ์—
01:14
Therefore, you're not accelerating.
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๊ฐ€์†๋˜์ง€ ์•Š๋Š” ๊ฑฐ์ฃ .
01:18
Newton's second law of motion -- net force equals mass times acceleration --
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๋‰ดํ„ด์˜ ์ œ2 ์šด๋™ ๋ฒ•์น™์€ - ์•Œ์งœํž˜์€ ์งˆ๋Ÿ‰ ๊ณฑํ•˜๊ธฐ ๊ฐ€์†๋„์™€ ๊ฐ™๋‹ค -
01:23
tells us that if the acceleration equals zero, the net force must equal zero.
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๊ฐ€์†๋„๊ฐ€ 0 ์ด๋ฉด ์•Œ์งœํž˜๋„ 0 ์ด ๋˜์–ด์•ผ ํ•จ์„ ๋งํ•ฉ๋‹ˆ๋‹ค.
01:29
Which means that the force of gravity pulling you down must be equal to the force of the scale pushing you up.
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๊ทธ๋ง์€ ์—ฌ๋Ÿฌ๋ถ„์„ ์•„๋ž˜๋กœ ๋‹น๊ธฐ๋Š” ์ค‘๋ ฅ์€ ์ €์šธ์ด ์—ฌ๋Ÿฌ๋ถ„์„ ๋ฐ€์–ด์˜ฌ๋ฆฌ๋Š” ํž˜๊ณผ ๊ฐ™์•„์•ผ ํ•จ์„ ๋œปํ•˜์ฃ .
01:39
Now let's suppose you're standing on that scale in an elevator.
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์ด์ œ ์—ฌ๋Ÿฌ๋ถ„์ด ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ ์•ˆ์—์„œ ์ €์šธ ์œ„์— ์„œ ์žˆ๋‹ค๊ณ  ๊ฐ€์ •ํ•ด๋ด…์‹œ๋‹ค.
01:44
At first, the elevator is standing still,
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์ฒ˜์Œ์—๋Š” ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ๋ฉˆ์ถฐ ์žˆ๊ณ 
01:47
so you and the scale are standing still.
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์—ฌ๋Ÿฌ๋ถ„๊ณผ ์ €์šธ๋„ ๋ฉˆ์ถฐ ์žˆ์–ด์š”.
01:51
The two forces on you are equal and opposite.
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์—ฌ๋Ÿฌ๋ถ„ํ•œํ…Œ ์ž‘์šฉํ•˜๋Š” ๋‘ ํž˜์€ ๊ฐ™์ง€๋งŒ ๋ฐ˜๋Œ€๋ฐฉํ–ฅ์ด์ฃ .
01:55
You can read how hard the scale is pushing by looking at it.
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์ €์šธ์ด ์–ผ๋งˆ๋‚˜ ์„ธ๊ฒŒ ๋ฐ€์–ด์˜ฌ๋ฆฌ๋Š”์ง€ ์—ฌ๋Ÿฌ๋ถ„์ด ์ €์šธ์„ ๋ณด๋ฉด ์•Œ ๊ฑฐ์—์š”.
01:59
We call that your weight.
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๊ทธ๊ฑธ ๋ชธ๋ฌด๊ฒŒ๋ผ๊ณ  ๋ถ€๋ฅด์ฃ .
02:01
Then, the elevator starts falling down.
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๊ทธ๋ฆฌ๊ณ ๋Š” ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ๋‚ด๋ ค๊ฐ‘๋‹ˆ๋‹ค.
02:04
You and the scale are in the elevator, so you are falling down too,
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์—ฌ๋Ÿฌ๋ถ„๊ณผ ์ €์šธ์ด ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ ์•ˆ์— ์žˆ๋Š”๋ฐ ์—ฌ๋Ÿฌ๋ถ„๋„ ๋‚ด๋ ค๊ฐ€๊ณ  ์žˆ์ฃ .
02:08
faster and faster.
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๋” ๋นจ๋ฆฌ, ๋”์šฑ ๋น ๋ฅด๊ฒŒ.
02:10
That means you are accelerating downward.
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๊ทธ๋ง์€ ์—ฌ๋Ÿฌ๋ถ„์—๊ฒŒ ์•„๋ž˜์ชฝ์œผ๋กœ ๊ฐ€์†๋„๊ฐ€ ๋ถ™๋Š”๋‹ค๋Š” ๋œป์ด์ฃ .
02:14
Now there is a net force in the same direction as the acceleration -- down.
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์ด์ œ ๊ฐ€์†๋„์™€ ๊ฐ™์€ ๋ฐฉํ–ฅ์œผ๋กœ ์•Œ์งœํž˜์ด ์žˆ์Šต๋‹ˆ๋‹ค.
02:22
Since gravity hasn't changed, that must mean the scale isn't pushing up as hard.
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์ค‘๋ ฅ์ด ๋ฐ”๋€Œ์ง€ ์•Š์•˜๊ธฐ ๋•Œ๋ฌธ์— ๊ทธ๋ง์€ ์ €์šธ์ด ์œ„๋กœ ์„ธ๊ฒŒ ๋ฐ€์–ด์˜ฌ๋ฆฌ์ง€ ์•Š๋Š”๋‹ค๋Š” ๋œป์ด์ฃ .
02:28
So the scale is reading a smaller number.
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๊ทธ๋ž˜์„œ ์ €์šธ ๋ˆˆ๊ธˆ์€ ์ž‘์€ ์ˆซ์ž๋ฅผ ๊ฐ€๋ฅดํ‚ต๋‹ˆ๋‹ค.
02:33
The faster the elevator accelerates, the less the scale pushes up.
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ๋” ๋น ๋ฅด๊ฒŒ ์†๋„๊ฐ€ ๋ถ™์„์ˆ˜๋ก ์ €์šธ์€ ์ ๊ฒŒ ๋ฐ€์–ด์˜ฌ๋ฆฌ์ฃ .
02:39
What if you jumped? Would you stop falling?
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์—ฌ๋Ÿฌ๋ถ„์ด ์ œ์ž๋ฆฌ์—์„œ ๋›ฐ๋ฉด ์–ด๋–ป๊ฒŒ ๋ ๊นŒ์š”? ์—ฌ๋Ÿฌ๋ถ„์ด ์•„๋ž˜๋กœ ๋–จ์–ด์ง€๋Š”๊ฒŒ ๋ฉˆ์ถฐ์งˆ๊นŒ์š”?
02:44
Would the elevator hit your head?
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ์—ฌ๋Ÿฌ๋ถ„ ๋จธ๋ฆฌ๋ฅผ ์น ๊นŒ์š”?
02:46
Well, what's pulling the elevator down? Gravity.
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๊ธ€์Ž„์š”, ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๋ฅผ ์•„๋ž˜๋กœ ๋‹น๊ธฐ๋Š” ๊ฒƒ์ด ๋ญก๋‹ˆ๊นŒ? ์ค‘๋ ฅ์ด์ฃ .
02:50
Is gravity pulling on you? Of course.
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์ค‘๋ ฅ์ด ์—ฌ๋Ÿฌ๋ถ„์„ ์žก์•„๋‹น๊ธฐ๋‚˜์š”? ๋‹น์—ฐํ•˜์ฃ .
02:54
So your relative position in the elevator will stay the same.
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์—˜๋ฆฌ๋ฒ ์ดํ„ฐ์—์„œ ์—ฌ๋Ÿฌ๋ถ„์˜ ์ƒ๋Œ€์ ์ธ ์œ„์น˜๋Š” ๊ฐ™์Šต๋‹ˆ๋‹ค.
02:58
The ceiling will only hit you if you can jump up to the ceiling.
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์ฒœ์ •์€ ์—ฌ๋Ÿฌ๋ถ„์ด ์ฒœ์ •๊นŒ์ง€ ๋›ฐ์–ด์•ผ๋งŒ ์—ฌ๋Ÿฌ๋ถ„์„ ์น  ๊ฑฐ์—์š”.
03:03
Now consider: what would happen if the elevator accelerated upward
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์ด์ œ ์ƒ๊ฐํ•ด๋ณด์„ธ์š”: ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๊ฐ€ ์œ„๋กœ ๊ฐ€์†ํ™”๋˜๋ฉด ์–ด๋–ค ์ผ์ด ๋ฒŒ์–ด์งˆ์ง€.
03:09
and, even more frightening, if someone snuck in and cut the cable holding the elevator,
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๋” ๋ฌด์„ญ๊ฒŒ๋Š” ๋ˆ„๊ตฐ๊ฐ€๊ฐ€ ๋ชฐ๋ž˜ ๋“ค์–ด์™€์„œ ์—˜๋ฆฌ๋ฒ ์ดํ„ฐ๋ฅผ ๋‹น๊ธฐ๋Š” ์ผ€์ด๋ธ”์„ ์ž๋ฅธ๋‹ค๋ฉด
03:15
what would happen then?
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๊ทธ๋•Œ๋Š” ๋ฌด์Šจ ์ผ์ด ๋ฒŒ์–ด์งˆ๊นŒ์š”?
03:18
Think about it.
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์ƒ๊ฐํ•ด๋ณด์„ธ์š”.
์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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