Home
登录
注册
学习内容
Loading...
听力练习
听力练习
/
Video
/
Be Smart
/
Why getting BACK from space is harder than getting there
Why getting BACK from space is harder than getting there
选择学习模式:
查看字幕
选词
重写单词
Highlight:
3000 Oxford Words
4000 IELTS Words
5000 Oxford Words
3000 Common Words
1000 TOEIC Words
5000 TOEFL Words
字幕 (58)
0:00
When a spaceship or meteor enters our
0:02
atmosphere, it becomes a fireball. But
0:04
that heat doesn't come from friction
0:07
with the atmosphere like most people
0:08
think. There's actually something way
0:10
more interesting going on. It takes so
0:12
much kinetic energy to get a spacecraft
0:14
to the moon. I mean, that's why the
0:16
rockets are so huge. But when you slow
0:18
down, all of that kinetic energy has to
0:20
go away somewhere, right? Well, you
0:22
could fire giant rockets to slow you
0:24
down and shave off some kinetic energy,
0:26
but you'd also have to carry all that
0:27
fuel up with you, too. That's why
0:29
spacecraft use the atmosphere as a break
0:31
instead. It's a genius way to take all
0:34
that kinetic energy and just convert it
0:36
to heat. Here's why friction isn't
0:38
what's happening. A spacecraft like
0:40
Orion slams into the atmosphere at
0:42
25,000 mph. That's something like 40
0:45
times faster than a passenger jet. At
0:48
that velocity, the air in front of the
0:50
spacecraft can't get out of the way. So,
0:52
it just gets squeezed and compressed
0:55
really violently. That heat is not from
0:58
air molecules rubbing against each
0:59
other. It's because the spacecraft acts
1:02
like a giant piston, compressing the air
1:04
into this impossibly thin layer. And
1:06
when you compress a gas, it heats up.
1:08
The air gets so hot as it gets squeezed,
1:11
it stops being air and becomes a
1:13
superheated plasma. It's a whole other
1:15
state of matter. That plasma can reach
1:18
10,000°,
1:19
hotter than the surface of the sun. And
1:21
it works really well. squishing the
1:24
atmosphere into a hot plasma removes
1:26
more than 99.9%
1:28
of Orion's kinetic energy before it
1:30
deploys those parachutes. And this is
1:32
why it's so important that space
1:34
capsules are the opposite of pointy
1:36
because that blunt shape creates a shock
1:38
wave that's pushed out away from the
1:40
surface. So almost all of that heat
1:42
stays out in front of the heat shield
1:44
and not touching the ship and the inside
1:47
of the spacecraft stays a comfortable
1:48
room temperature. Sharp, streamlined
1:51
shapes, which works basically everywhere
1:52
else in aerodynamics, actually makes
1:54
re-entry worse. And that's why every
1:56
crude capsule ever built is shaped like
1:58
a pudgy little cone. Follow me for more
2:01
cool science videos.
Why getting BACK from space is harder than getting there - Video học tiếng Anh
