How rollercoasters affect your body - Brian D. Avery

2,473,406 views ใƒป 2018-10-29

TED-Ed


ืื ื ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ืœืžื˜ื” ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ.

ืชืจื’ื•ื: Ido Dekkers ืขืจื™ื›ื”: Allon Sasson
00:06
In the summer of 1895, crowds flooded the Coney Island boardwalk
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ื‘ืงื™ืฅ 1895, ื”ืžื•ื ื™ื ื”ืฆื™ืคื• ืืช ื˜ื™ื™ืœืช ืงื•ื ื™ ืื™ื™ืœื ื“
00:12
to see the latest marvel of roller coaster technology:
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ื›ื“ื™ ืœืจืื•ืช ืืช ื”ืคืœื ื”ืื—ืจื•ืŸ ืฉืœ ื˜ื›ื ื•ืœื•ื’ื™ื™ืช ืจื›ื‘ื•ืช ื”ื”ืจื™ื:
00:16
the Flip Flap Railway.
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ืจื›ื‘ืช ื”ืคืœื™ืค ืคืœื•ืค.
00:18
This was Americaโ€™s first-ever looping coaster
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ื–ื• ื”ื™ืชื” ืจื›ื‘ืช ื”ื”ืจื™ื ื”ืจืืฉื•ื ื” ื‘ืืจืฆื•ืช ื”ื‘ืจื™ืช ืฉื›ืœืœื” ืœื•ืค
00:21
โ€“ but its thrilling flip came at a price.
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-- ืื‘ืœ ื”ื”ื™ืคื•ืš ื”ืžืจื’ืฉ ืฉืœื” ื”ื’ื™ืข ืขื ืžื—ื™ืจ.
00:24
The ride caused numerous cases of severe whiplash,
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ื”ื ืกื™ืขื” ื’ืจืžื” ืœืžืงืจื™ื ืžืจื•ื‘ื™ื ืฉืœ ืฆืœื™ืคืช ืฆื•ื•ืืจ ื—ืžื•ืจื”,
00:28
neck injury and even ejections,
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ืคืฆื™ืขื•ืช ืฆื•ื•ืืจ ื•ืืคื™ืœื• ืคืœื™ื˜ื•ืช,
00:31
all due to its signature loop.
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ื”ื›ืœ ื‘ื’ืœืœ ื”ืœื•ืค ื”ืžืืคื™ื™ืŸ.
00:33
Today, coasters can pull off far more exciting tricks,
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ื”ื™ื•ื, ืจื›ื‘ื•ืช ื™ื›ื•ืœื•ืช ืœื‘ืฆืข ื˜ืจื™ืงื™ื ื”ืจื‘ื” ื™ื•ืชืจ ืžืจื’ืฉื™ื,
00:37
without resorting to the โ€œthrillโ€ of a hospital visit.
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ื‘ืœื™ ืœื”ื’ื™ืข ืœ"ืจื™ื’ื•ืฉ" ืฉืœ ื‘ื™ืงื•ืจ ื‘ื‘ื™ืช ื”ื—ื•ืœื™ื.
00:40
But what exactly are roller coasters doing to your body,
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ืื‘ืœ ืžื” ื‘ื“ื™ืง ืจื›ื‘ื•ืช ื”ืจื™ื ืขื•ืฉื•ืช ืœื’ื•ืฃ ืฉืœื›ื,
00:44
and how have they managed to get scarier and safer at the same time?
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ื•ืื™ืš ื”ืŸ ื”ืฆืœื™ื—ื• ืœื”ื™ื•ืช ืžืคื—ื™ื“ื•ืช ื™ื•ืชืจ ื•ื‘ื˜ื•ื—ื•ืช ื™ื•ืชืจ ื‘ืื•ืชื• ื–ืžืŸ?
00:48
At the center of every roller coaster design is gravity.
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ื‘ืžืจื›ื– ื›ืœ ืขื™ืฆื•ื‘ ืจื›ื‘ืช ื”ืจื™ื ื ืžืฆืืช ื”ื›ื‘ื™ื“ื”.
00:53
Unlike cars or transit trains,
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ื‘ื ื™ื’ื•ื“ ืœืžื›ื•ื ื™ื•ืช ืื• ืจื›ื‘ื•ืช,
00:55
most coasters are propelled around their tracks
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ืจื•ื‘ ืจื›ื‘ื•ืช ื”ื”ืจื™ื ืžื•ื ืขื•ืช ืขืœ ื”ืžืกื™ืœื•ืช ืฉืœื”ืŸ
00:58
almost entirely by gravitational energy.
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ื›ืžืขื˜ ืœื’ืžืจื™ ืขืœ ื™ื“ื™ ืื ืจื’ื™ืช ื›ื‘ื™ื“ื”.
01:01
After the coaster crests the initial lift hill,
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ืื—ืจื™ ืฉื”ืจื›ื‘ืช ืขื•ื‘ืจืช ืืช ื”ืฉื™ื ื”ืจืืฉื•ืŸ,
01:04
it begins an expertly engineered cycle โ€“
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ื”ื™ื ืžืชื—ื™ืœื” ืžื—ื–ื•ืจ ืžื”ื•ื ื“ืก ื‘ืžื•ืžื—ื™ื•ืช --
01:08
building potential energy on ascents and expending kinetic energy on descents.
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ืฆื•ื‘ืจืช ืื ืจื’ื™ื” ืคื•ื˜ื ืฆื™ืืœื™ืช ื‘ืขืœื™ื” ื•ืžื•ืฆื™ืื” ืื ืจื’ื™ื” ืงื™ื ื˜ื™ืช ื‘ื™ืจื™ื“ื”.
01:13
This rhythm repeats throughout the ride,
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ื”ืžื—ื–ื•ืจ ื”ื–ื” ื—ื•ื–ืจ ืœื›ืœ ืื•ืจืš ื”ื ืกื™ืขื”,
01:16
acting out the coaster engineerโ€™s choreographed dance
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ืžื‘ืฆืขืช ืืช ื”ืจื™ืงื•ื“ ืฉืชื›ื ืŸ ื”ื›ื•ืจื™ืื•ื’ืจืฃ ื”ืžื”ื ื“ืก
01:19
of gravitational energy.
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ื‘ืืžืฆืขื•ืช ืื ืจื’ื™ืช ื›ื‘ื™ื“ื”.
01:21
But thereโ€™s a key variable in this cycle that wasnโ€™t always so carefully considered:
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ืื‘ืœ ื™ืฉ ืžืฉืชื ื” ืžืคืชื— ื‘ืžื—ื–ื•ืจ ืฉืœื ืชืžื™ื“ ืžืชื—ืฉื‘ื™ื ื‘ื• ื‘ื–ื”ื™ืจื•ืช ืจื‘ื”:
01:26
you.
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ืืชื.
01:27
In the days of the Flip-Flap,
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ื‘ื™ืžื™ื ืฉืœ ื”ืคืœื™ืค ืคืœื•ืค,
01:29
ride designers were most concerned with coasters getting stuck
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ืžืชื›ื ื ื™ ืžืชืงื ื™ื ื”ื™ื• ืžื•ื“ืื’ื™ื ื‘ืขื™ืงืจ ืฉื”ืจื›ื‘ื•ืช ืœื ื™ืชืงืขื•
01:32
somewhere along the track.
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ื”ื™ื›ืŸ ืฉื”ื•ื ืขืœ ื”ืžืกื™ืœื”.
01:34
This led early builders to overcompensate,
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ื–ื” ื”ื•ื‘ื™ืœ ื‘ื•ื ื™ื ืžื•ืงื“ืžื™ื ืœืคื™ืฆื•ื™ ื™ืชืจ,
01:36
hurling trains down hills
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ืฉื™ื’ื•ืจ ืจื›ื‘ื•ืช ื‘ืžื•ืจื“ ื’ื‘ืขื•ืช
01:38
and pulling on the brakes when they reached the station.
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ื•ืžืฉื™ื›ืช ื”ื‘ืœืžื™ื ื›ืฉื”ืŸ ื”ื’ื™ืขื• ืœืชื—ื ื”.
01:41
But as gravity affects the cars, it also affects the passengers.
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ืื‘ืœ ื›ืžื• ืฉื”ื›ื‘ื™ื“ื” ืžืฉืคื™ืขื” ืขืœ ื”ืงืจื•ื ื•ืช ื”ื™ื ื’ื ืžืฉืคื™ืขื” ืขืœ ื”ื ื•ืกืขื™ื.
01:45
And under the intense conditions of a coaster,
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ื•ืชื—ืช ื”ืชื ืื™ื ื”ืงื™ืฆื•ื ื™ื™ื ืฉืœ ืจื›ื‘ืช ื”ื”ืจื™ื,
01:48
gravityโ€™s effects are multiplied.
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ื”ืฉืคืขื•ืช ื”ื›ื‘ื™ื“ื” ืžื•ื›ืคืœื•ืช.
01:50
Thereโ€™s a common unit used by jet pilots,
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ื™ืฉ ื™ื—ื™ื“ื” ื ืคื•ืฆื” ื‘ืฉื™ืžื•ืฉ ืฉืœ ื˜ื™ื™ืกื™ ืงืจื‘,
01:53
astronauts,
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01:53
and coaster designers called โ€œg forceโ€.
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ืืกื˜ืจื•ื ืื•ื˜ื™ื,
ื•ืžืชื›ื ื ื™ ืจื›ื‘ื•ืช ื”ืจื™ื ืฉื ืงืจืืช ื›ื•ื— ื’'ื™.
01:57
One G force is the familiar tug of gravity you feel when standing on Earth
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ื›ื•ื— ื’'ื™ ืื—ื“ ื”ื•ื ื”ืžืฉื™ื›ื” ื”ืžื•ื›ืจืช ืฉืœ ื”ื›ื‘ื™ื“ื” ืฉืืชื ืžืจื’ื™ืฉื™ื ื›ืฉืืชื ืขื•ืžื“ื™ื ืขืœ ื›ื“ื•ืจ ื”ืืจืฅ
02:01
โ€“ this is the force of Earthโ€™s gravitational pull on our bodies.
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-- ื–ื” ื”ื›ื•ื— ืฉืœ ื”ืžืฉื™ื›ื” ื”ื›ื‘ื™ื“ืชื™ืช ืขืœ ื”ื’ื•ืฃ ืฉืœื ื•.
02:05
But as riders accelerate and decelerate,
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ืื‘ืœ ื›ืฉื ื•ืกืขื™ื ืžืื™ืฆื™ื ื•ืžืื™ื˜ื™ื,
02:08
they experience more or less gravitational force.
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ื”ื ื—ื•ื•ื™ื ื™ื•ืชืจ ืื• ืคื—ื•ืช ื›ื•ื— ื›ื‘ื™ื“ืชื™.
02:12
Modern ride designers know that the body can handle up to roughly 5 Gs,
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ืžืชื›ื ื ื™ ืžืชืงื ื™ื ืžื•ื“ืจื ื™ื™ื ื™ื•ื“ืขื™ื ืฉื”ื’ื•ืฃ ื™ื›ื•ืœ ืœื”ืชืžื•ื“ื“ ืขื ืขื“ 5 ื’'ื™,
02:17
but the Flip-Flap and its contemporaries routinely reached up to 12 Gs.
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ืื‘ืœ ื”ืคืœื™ืค ืคืœืืค ื•ื”ืจื›ื‘ื•ืช ื‘ืชืงื•ืคืชื” ื”ื’ื™ืขื• ื‘ืงื‘ื™ืขื•ืช ืขื“ 12 ื’'ื™.
02:22
At those levels of gravitational pressure,
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ื‘ืื•ืชืŸ ืจืžื•ืช ืฉืœ ืœื—ืฅ ื›ื‘ื™ื“ืชื™,
02:24
blood is sent flying from your brain to your feet,
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ื”ื“ื ื ืฉืœื— ืžื”ืžื•ื— ืœืจื’ืœื™ื,
02:27
leading to light-headedness or blackouts
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ืžื” ืฉืžื•ื‘ื™ืœ ืœืกื—ืจื—ื•ืจืช ืื• ืื™ื‘ื•ื“ื™ ื”ื›ืจื”
02:30
as the brain struggles to stay conscious.
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ื›ืฉื”ืžื•ื— ืžืชืืžืฅ ืœื”ืฉืืจ ื‘ื”ื›ืจื”.
02:32
And oxygen deprivation in the retinal cells impairs their ability to process light,
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ื•ื”ืจืขื‘ืช ื—ืžืฆืŸ ื‘ืชืื™ ื”ืจืฉืชื™ืช ืžืฉืคื™ืขื” ืขืœ ื”ื™ื›ื•ืœืช ืœืขื‘ื“ ืื•ืจ,
02:38
causing greyed out vision or temporary blindness.
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ืžื” ืฉื’ื•ืจื ืœืจืื™ื” ืžื•ืืคืจืช ืื• ืขื™ื•ื•ืจื•ืŸ ื–ืžื ื™.
02:41
If the riders are upside down, blood can flood the skull,
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ืื ื”ื ื•ืกืขื™ื ื”ืคื•ื›ื™ื, ื“ื ื™ื›ื•ืœ ืœื”ืฆื™ืฃ ืืช ื”ื’ื•ืœื’ื•ืœืช,
02:45
causing a bout of crimson vision called a โ€œredoutโ€.
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ืžื” ืฉื’ื•ืจื ืœืจืื™ื” ืื“ื•ืžื” ืฉื ืงืจืืช ืจื“ืืื•ื˜.
02:49
Conversely, negative Gโ€™s create weightlessness.
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ื‘ื ื™ื’ื•ื“, ื’'ื™ ืฉืœื™ืœื™ ื™ื•ืฆืจ ื—ื•ืกืจ ืžืฉืงืœ.
02:53
Within the body,
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ื‘ืชื•ืš ื”ื’ื•ืฃ,
02:54
short-term weightlessness is mostly harmless.
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ื—ื•ืกืจ ืžืฉืงืœ ืœื˜ื•ื•ื— ืงืฆืจ ืœื ืžื–ื™ืง ื‘ืจื•ื‘ื•.
02:57
It can contribute to a riderโ€™s motion sickness
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ื”ื•ื ื™ื›ื•ืœ ืœืชืจื•ื ืœื ื•ืกืขื™ื ืžื—ืœืช ืชื ื•ืขื”
02:59
by suspending the fluid in their inner ears
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ืขืœ ื™ื“ื™ ืชืœื™ื™ืช ื”ื ื•ื–ืœื™ื ื‘ืื•ื–ืŸ ื”ืคื ื™ืžื™ืช
03:02
which coordinates balance.
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ืฉืžืชืืžืช ืฉื™ื•ื•ื™ ืžืฉืงืœ.
03:03
But the bigger potential danger
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ืื‘ืœ ื”ืกื›ื ื” ื”ืคื•ื˜ื ืฆื™ืืœื™ืช ื”ื’ื“ื•ืœื” ื™ื•ืชืจ
03:05
โ€“ and thrill โ€“
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- ื•ื”ืจื™ื’ื•ืฉ -
03:06
comes from what ride designers call airtime.
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ืžื’ื™ืข ืžืžื” ืฉื”ืžืชื›ื ื ื™ื ืงื•ืจืื™ื ืœื• ื–ืžืŸ ืื•ื™ืจ.
03:09
This is when riders typically experience seat separation,
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ืื– ื”ื ื•ืกืขื™ื ื‘ืื•ืคืŸ ื˜ื™ืคื•ืกื™ ื—ื•ื•ื™ื ื”ืชื ืชืงื•ืช ื”ืžื•ืฉื‘,
03:13
and, without the proper precautions,
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ื•ื‘ืœื™ ื”ื’ื ื•ืช ืžืชืื™ืžื•ืช,
03:14
ejection.
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ืคืœื™ื˜ื”.
03:15
The numerous belts and harnesses of modern coasters
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ื”ื—ื’ื•ืจื•ืช ื•ื”ืจืชืžื•ืช ื”ืžืจื•ื‘ื•ืช ืฉืœ ืจื›ื‘ื•ืช ื”ืจื™ื ืžื•ื“ืจื ื™ื•ืช
03:18
have largely solved this issue,
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ืคืชืจื• ื›ืžืขื˜ ืœื—ืœื•ื˜ื™ืŸ ืืช ื”ื‘ืขื™ื”,
03:20
but the passengerโ€™s ever-changing position can make it difficult
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ืื‘ืœ ืฉื™ื ื•ื™ ื”ืžืงื•ื ื”ืžืฉืชื ื” ืชืžื™ื“ื™ืช ืฉืœ ื”ื ื•ืกืขื™ื ื™ื›ื•ืœ ืœืขืฉื•ืช ืืช ื–ื” ืœืงืฉื”
03:24
to determine what needs to be strapped down.
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ืœืงื‘ื•ืข ืžื” ืฆืจื™ืš ืœื”ืงืฉืจ.
03:26
Fortunately, modern ride designers are well aware
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ืœืžืจื‘ื” ื”ืžื–ืœ, ืžืชื›ื ื ื™ ืžืชืงื ื™ื ืžื•ื“ืจื ื™ื™ื ืžื•ื“ืขื™ื
03:29
of what your body, and the coaster,
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ืœืžื” ืฉื”ื’ื•ืฃ ืฉืœื›ื, ื•ื”ืจื›ื‘ื•ืช,
03:31
can handle.
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ื™ื›ื•ืœื™ื ืœืžืชืžื•ื“ื“.
03:32
Coaster engineers play these competing forces against each other,
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ืžื”ื ื“ืกื™ ืจื›ื‘ื•ืช ื”ืจื™ื ืžืฉื—ืงื™ื ืขื ื”ื›ื•ื—ื•ืช ื”ืžืชื—ืจื™ื ื”ืืœื” ืื—ื“ ื ื’ื“ ื”ืฉื ื™,
03:36
to relieve periods of intense pressure with periods of no pressure at all.
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ื›ื“ื™ ืœืฉื—ืจืจ ืชืงื•ืคื•ืช ืฉืœ ืœื—ืฅ ื—ื–ืง ืขื ืชืงื•ืคื•ืช ื ื˜ื•ืœื•ืช ืœื—ืฅ ืœื’ืžืจื™.
03:40
And since a quick transition from positive to negative G-force
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ื•ืžืื—ืจ ื•ืžืขื‘ืจ ืžื”ื™ืจ ื‘ื™ืŸ ื›ื•ื—ื•ืช ื’'ื™ ื—ื™ื•ื‘ื™ื™ื ืœืฉืœื™ืœื™ื™ื
03:43
can result in whiplash, headaches, and back and neck pain,
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ื™ื›ื•ืœ ืœื’ืจื•ื ืœืฆืœื™ืคืช ืฆื•ื•ืืจ, ื›ืื‘ื™ ืจืืฉ, ื•ื›ืื‘ื™ ื’ื‘ ื•ืฆื•ื•ืืจ,
03:47
they avoid the extreme changes in speed and direction
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ื”ื ื ืžื ืขื™ื ืžืฉื™ื ื•ื™ื™ื ืงื™ืฆื•ื ื™ื™ื ื‘ืžื”ื™ืจื•ืช ื•ื›ื™ื•ื•ืŸ
03:50
so common in thrill rides of old.
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ืฉื›ืœ ื›ืš ื ืคื•ืฆื™ื ื‘ืจื›ื‘ื•ืช ืžื”ืขื‘ืจ.
03:53
Modern rides are also much sturdier,
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ืžืชืงื ื™ื ืžื•ื“ืจื ื™ื™ื ื”ืจื‘ื” ื™ื•ืชืจ ืขืžื™ื“ื™ื,
03:56
closely considering the amount of gravity they need to withstand.
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ื•ืฉื•ืงืœื™ื ื‘ืžื“ื•ื™ื™ืง ืืช ื›ืžื•ืช ื”ื›ื‘ื™ื“ื” ื‘ื”ื ื”ื ืฆืจื™ื›ื™ื ืœืขืžื•ื“.
03:59
At 5 Gโ€™s, your body feels 5 times heavier;
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ื‘ 5 ื’ื™', ื”ื’ื•ืฃ ืฉืœื›ื ืžืจื’ื™ืฉ ื›ื‘ื“ ืคื™ 5,
04:03
so if you weigh 100lbs,
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ืื– ืื ืืชื ืฉื•ืงืœื™ื 50 ืงื™ืœื•,
04:04
youโ€™d exert the weight of 500 lbs on the coaster.
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ืืชื ืชืคืขื™ืœื• 250 ืงื™ืœื• ื›ื•ื— ืขืœ ืจื›ื‘ืช ื”ื”ืจื™ื.
04:08
Engineers have to account for the multiplied weight
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ืžื”ื ื“ืกื™ื ื—ื™ื™ื‘ื™ื ืœื”ืชื—ืฉื‘ ื‘ืžืฉืงืœื™ื ื”ืžื•ื›ืคืœื™ื ื”ืืœื”
04:11
of every passenger when designing a coasterโ€™s supports.
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ืฉืœ ื›ืœ ื ื•ืกืข ื›ืฉื”ื ืžืชื›ื ื ื™ื ืืช ื”ืชื•ืžื›ื•ืช ืฉืœ ืจื›ื‘ืช ื”ื”ืจื™ื.
04:15
Still, these rides arenโ€™t for everyone.
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ื•ืขื“ื™ื™ืŸ, ื”ืžืชืงื ื™ื ื”ืืœื” ืœื ืœื›ื•ืœื.
04:17
The floods of adrenaline, light-headedness, and motion sickness
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ื”ืฆืคืช ื”ืื ื“ืจื ืœื™ืŸ, ืงืœื•ืช ื”ืจืืฉ, ื•ืžื—ืœืช ื”ืชื ื•ืขื”
04:21
arenโ€™t going anywhere soon.
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ืœื ื™ืขืœืžื• ื‘ืงืจื•ื‘.
04:23
But todayโ€™s redundant restraints, 3D modeling and simulation software
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ืื‘ืœ ื”ืจืชืžื•ืช ื”ื ื•ืกืคื•ืช ื”ื™ื•ื, ืžื™ื“ื•ืœ ืชืœืช ืžื™ืžื“ื™ ื•ืชื•ื›ื ื•ืช ื”ื“ืžื™ื™ื”
04:28
have made roller coasters safer and more thrilling than ever.
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ื”ืคื›ื• ืจื›ื‘ื•ืช ื”ืจื™ื ืœื‘ื˜ื•ื—ื•ืช ื™ื•ืชืจ ื•ืžืจื’ืฉื•ืช ื™ื•ืชืจ ืžืื™ ืคืขื.
04:32
Our precise knowledge about the limits of the human body
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ื”ื™ื“ืข ื”ืžื“ื•ื™ื™ืง ืฉืœื ื• ื‘ื ื•ื’ืข ืœื’ื‘ื•ืœื•ืช ืฉืœ ื”ื’ื•ืฃ ื”ืื ื•ืฉื™
04:34
have helped us build coasters that are faster, taller, and loopier
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ืขื–ืจื• ืœื ื• ืœื‘ื ื•ืช ืจื›ื‘ื•ืช ืžื”ื™ืจื•ืช, ื’ื‘ื•ื”ื•ืช ื•ืœื•ืคื™ื•ืช ื™ื•ืชืจ
04:38
โ€“ and all without going off the rails.
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-- ื•ื”ื›ืœ ื‘ืœื™ ืœืจื“ืช ืžื”ืคืกื™ื.
ืขืœ ืืชืจ ื–ื”

ืืชืจ ื–ื” ื™ืฆื™ื’ ื‘ืคื ื™ื›ื ืกืจื˜ื•ื ื™ YouTube ื”ืžื•ืขื™ืœื™ื ืœืœื™ืžื•ื“ ืื ื’ืœื™ืช. ืชื•ื›ืœื• ืœืจืื•ืช ืฉื™ืขื•ืจื™ ืื ื’ืœื™ืช ื”ืžื•ืขื‘ืจื™ื ืขืœ ื™ื“ื™ ืžื•ืจื™ื ืžื”ืฉื•ืจื” ื”ืจืืฉื•ื ื” ืžืจื—ื‘ื™ ื”ืขื•ืœื. ืœื—ืฅ ืคืขืžื™ื™ื ืขืœ ื”ื›ืชื•ื‘ื™ื•ืช ื‘ืื ื’ืœื™ืช ื”ืžื•ืฆื’ื•ืช ื‘ื›ืœ ื“ืฃ ื•ื™ื“ืื• ื›ื“ื™ ืœื”ืคืขื™ืœ ืืช ื”ืกืจื˜ื•ืŸ ืžืฉื. ื”ื›ืชื•ื‘ื™ื•ืช ื’ื•ืœืœื•ืช ื‘ืกื ื›ืจื•ืŸ ืขื ื”ืคืขืœืช ื”ื•ื•ื™ื“ืื•. ืื ื™ืฉ ืœืš ื”ืขืจื•ืช ืื• ื‘ืงืฉื•ืช, ืื ื ืฆื•ืจ ืื™ืชื ื• ืงืฉืจ ื‘ืืžืฆืขื•ืช ื˜ื•ืคืก ื™ืฆื™ืจืช ืงืฉืจ ื–ื”.

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