跟读练习: How High Can Birds Fly? - 通过视频学习英语口语

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In 1973, an airliner struck a bird called a Rupel's Griffin vulture, which on its own isn't that weird.

Planes hit birds pretty regularly during takeoffs and landings.

But this collision happened at a cruising height of over 11,000 meters.

That's way above the height at which most birds fly.

Which makes me wonder, what is the highest a bird can actually fly?

Hi, I'm Cameron and this is MinuteEarth.

Birds don't tend to fly higher than they absolutely need to, for the same reason you You don't sprint when you could walk.

It's difficult and tiring.

So we can't necessarily get the answer to this question through observation.

I mean, I guess we could drop a bunch of birds out of airplanes and see what happens, but our AdSense revenue definitely isn't going to cover that.

Plus, we're not monsters.

So let's use our understanding of aerodynamics, scaling laws, and biology to science our way to an approximate answer.

There are two things that limit how high a bird can fly.

Its ability to stay aloft as the air pressure decreases, and on a much more basic level, its ability to stay alive as the temperature and amount of oxygen decreases.

So first, let's figure out which bird could survive at the highest altitude.

Oxygen supplies birds the energy they need to stay warm, but at higher altitudes there's less oxygen available and the temperature is much colder,

so a bird's ability to survive high up in the air depends on how efficiently they use oxygen

and how well they can retain body heat paper measured the oxygen use of a handful of birds and found that, very generally, their overall oxygen use increases with mass.

We can then adjust according to other traits, like how much energy their flight muscles require and how much insulation their feathers provide.

From all of this, we can calculate the altitude at which each bird should suffer from hypothermia.

Let's call this their popsicle point.

If we then compile a data set of flying birds and plug their data into these equations, we can see a general pattern emerge.

Larger birds can theoretically survive at higher altitudes than smaller birds.

There are exceptions, of course, this is biology after all, but our calculations suggest that there are a bunch of birds that could potentially survive above 10,000 meters.

And the largest bird in our dataset, the wandering albatross, might be able to survive as high as 17,000 meters.

But remember, we also need to figure out if any of these birds could actually stay aloft at such high altitudes.

Because the air is less dense the higher you go, less air is available at higher altitudes to push upward against a bird's wings and create that lift.

A bird's ability to stay aloft high in the air depends on its weight, size of its wings, and the shape and angle of attack of its wings.

That's a factor called the lift coefficient.

Combining all of that tells us how much lift a bird's wings should generate in still air at a given altitude.

Simple enough at first.

But while weights and wingspans and whatnot are easy enough to measure, the wing shapes and angles aren't.

Because a bird's wing shape changes as it flies.

I'll save you the long explanation of my rationale here, and just say that this is about where I go out on a bit of a limb.

The lift coefficient for the birds in our dataset peaks at about 1.5 or so, and that's when they're taking off or about to stall.

In other words, when the bird is trying hardest to generate lift.

And since staying aloft is likely a struggle at a bird's maximum altitude, this is probably a pretty good estimate of the lift coefficient at this point.

From there, we can find the lowest air pressure at which each bird could generate sufficient lift to keep its mass aloft, and then use our friend the barometric equation to convert those

numbers to altitudes to estimate the highest point each bird in our dataset should be able to actually maintain flight.

Let's call this their lift limit.

In general, the smaller birds have the highest lift limits.

The hulking Muteswan would struggle to generate lift at a mere 3,800 meters, while the puny Sandmartin should be able to glide at nearly 19,000 meters.

Of course, air moves and it's not uniformly dense at given altitudes, so there's definitely some wiggle room here, which will be a surprise tool that's going to help us later.

But in any case, a bird with a higher lift limit should be able to fly higher than a bird with a lower one.

Now let's combine our lift limit data with our popsicle point data.

We can see that lots of birds, like the missile thrush, can theoretically fly super high, but would freeze long before they got there.

And then there are a bunch of other birds, like the wandering albatross, that could likely survive at super high altitudes but wouldn't be able to actually maintain flight up there.

That leaves us with a small cluster of birds with relatively high popsicle points and high lift limits.

Mathematically, these should be the highest flying birds, and for the most part, they're geese.

The greylag goose, the bean goose, the Canada goose, and the bar-headed goose should be able to fly as high as 8,000 meters or so,

according to our calculations, and this matches up pretty well with what scientists have actually observed.

Like during its migration over the highest mountain range on the planet, the bar-headed goose can reach altitudes of over 7,000 meters.

Then there's the white stork, which based on its popsicle point and lift limit, is our predicted highest flying bird.

It could potentially fly up to about 10,500 meters.

In reality, it doesn't fly anywhere near that high.

But remember, birds don't necessarily fly as high as they might be physically capable of.

But wait, what about the Rupal's griffin?

A bird we know for a fact can fly higher than 11,000 meters.

Our math suggests that it is lift limited a lot lower than that, about 8200 meters.

But this is where theoretical calculations fall short without some additional real-world knowledge.

See, the RuPaul's Griffin likes to soar on thermals, warm columns of rising air that can help birds exceed their mathematical lift limit,

sometimes even thousands of extra meters up into the air.

Other birds are also known to ride thermals, but none of the other high popsicle point birds ride such supercharged thermals, so the Rupples Griffin is likely the bird capable of the highest flight,

with the right thermal.

It might even reach its very generous popsicle point of 15,000 meters.

Turns out, that bird might have had a lot of climbing left to do.

You might have noticed that this video is chock full of all sorts of calculations

that I basically ripped my hair out trying to make sure I got right.

It would have been great if I had a brilliant tutor sitting next to me guiding my learning.

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Thanks Brilliant!

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FOR YOU

本课的词汇与口语要点

这段视频共有 77 个句子、1297 个单词可供跟读。讲话部分时长为 6:44。说话人语速较快，每分钟约 193 个词，会出现较多连读和弱读。只有 79% 的单词属于英语最常用的 3,000 词，词汇难度较高。

视频中的重点词汇

视频中 15 个值得学习的单词，附发音和释义：

单词	发音	释义
meter 名词	/ˈmitəɹ/	計量表 /计量表
oxygen 名词	/ˈɑksɪd͡ʒən/	氧
goose 名词	/ɡus/	鵝 /鹅, 雁
griffin 名词	/ˈɡɹɪf.ɪn/	獅鷲 /狮鹫
calculation 名词	/ˌkælkjuˈleɪʃn̩/	計算 /计算
tutor 名词	/ˈtjuːtəː/	私人教師 /私人教师, 家庭教師 /家庭教师
necessarily 副词	/ˌnɛs.əˈsɛɹ.ə.li/	必然地, 必定地
angle 名词	/ˈæŋ.ɡəl/	角, 角度
estimate 名词	/ˈɛs.tɪ.mət/	估計 /估计
biology 名词	/baɪˈɑ.lə.d͡ʒi/	生物學 /生物学
depend 动词	/dɪˈpɛnd/	信任, 信賴 /信赖
decrease 动词	/dɪˈkɹiːs/	減少 /减少, 下降
mathematics 名词	/mæθ(.ə)ˈmæt.ɪks/	數學 /数学, 算學 /算学
combine 动词	/kəmˈbaɪn/	結合 /结合, 組合 /组合
equation 名词	/ɪˈkweɪ.ʒən/	方程式, 方程

视频中出现的短语动词

单词	释义
figure out 动词	弄清楚
take off 动词	脫 /脱
turn out 动词	原來 /原来

需要注意的发音

说话人用了 15 次缩略和弱读形式，例如 don't, isn't, they're。请按听到的简短形式来说。

“th” 音: mathematics /mæθ(.ə)ˈmæt.ɪks/, mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, thermal /ˈθɜːməl/, theoretical /ˌθi.əˈɹɛt.ɪ.kəl/, feather /ˈfɛðə/
“sh” 和 “zh” 音: calculation /ˌkælkjuˈleɪʃn̩/, potentially /pəˈtɛnʃ(ə)li/, equation /ɪˈkweɪ.ʒən/, explanation /ˌɛkspləˈneɪʃən/, exception /əkˈsɛpʃən/
长单词——注意重音位置: necessarily /ˌnɛs.əˈsɛɹ.ə.li/, potentially /pəˈtɛnʃ(ə)li/, biology /baɪˈɑ.lə.d͡ʒi/, mathematics /mæθ(.ə)ˈmæt.ɪks/, explanation /ˌɛkspləˈneɪʃən/

如何用这段视频练习

先完整听一遍视频，不要开口，记下不认识的单词。
先用 0.75 倍速逐句跟读，熟练之后再回到正常速度。
录下自己的声音并与原声对比，特别注意 meter, oxygen, goose 这类单词。

什么是跟读法？

跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。

影子跟读法: 阅读完整分步指南 →

跟读练习: How High Can Birds Fly? - 通过视频学习英语口语

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