Luyện nói tiếng Anh bằng Shadowing qua video: How High Can Birds Fly?
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77 câu
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1
In 1973, an airliner struck a bird called a Rupel's Griffin vulture, which on its own isn't that weird.
Năm 1973, một chiếc máy bay hàng không đã va chạm với một con chim thuộc loài kền kền Rupell, mà bản thân sự việc này không hề có gì kỳ lạ.
2
Planes hit birds pretty regularly during takeoffs and landings.
Máy bay va chạm với chim khá thường xuyên trong quá trình cất cánh và hạ cánh.
3
But this collision happened at a cruising height of over 11,000 meters.
Nhưng vụ va chạm này xảy ra ở độ cao bay hành trình trên 11.000 mét.
4
That's way above the height at which most birds fly.
Đó cao hơn nhiều so với độ cao mà hầu hết các loài chim bay.
5
Which makes me wonder, what is the highest a bird can actually fly?
6
Hi, I'm Cameron and this is MinuteEarth.
7
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.
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It's difficult and tiring.
9
So we can't necessarily get the answer to this question through observation.
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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.
11
Plus, we're not monsters.
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So let's use our understanding of aerodynamics, scaling laws, and biology to science our way to an approximate answer.
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There are two things that limit how high a bird can fly.
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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.
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So first, let's figure out which bird could survive at the highest altitude.
16
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,
17
so a bird's ability to survive high up in the air depends on how efficiently they use oxygen
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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.
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We can then adjust according to other traits, like how much energy their flight muscles require and how much insulation their feathers provide.
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From all of this, we can calculate the altitude at which each bird should suffer from hypothermia.
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Let's call this their popsicle point.
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If we then compile a data set of flying birds and plug their data into these equations, we can see a general pattern emerge.
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Larger birds can theoretically survive at higher altitudes than smaller birds.
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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.
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And the largest bird in our dataset, the wandering albatross, might be able to survive as high as 17,000 meters.
26
But remember, we also need to figure out if any of these birds could actually stay aloft at such high altitudes.
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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.
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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.
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That's a factor called the lift coefficient.
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Combining all of that tells us how much lift a bird's wings should generate in still air at a given altitude.
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Simple enough at first.
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But while weights and wingspans and whatnot are easy enough to measure, the wing shapes and angles aren't.
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Because a bird's wing shape changes as it flies.
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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.
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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.
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In other words, when the bird is trying hardest to generate lift.
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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.
38
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
39
numbers to altitudes to estimate the highest point each bird in our dataset should be able to actually maintain flight.
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Let's call this their lift limit.
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In general, the smaller birds have the highest lift limits.
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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.
43
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.
44
But in any case, a bird with a higher lift limit should be able to fly higher than a bird with a lower one.
45
Now let's combine our lift limit data with our popsicle point data.
46
We can see that lots of birds, like the missile thrush, can theoretically fly super high, but would freeze long before they got there.
47
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.
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That leaves us with a small cluster of birds with relatively high popsicle points and high lift limits.
49
Mathematically, these should be the highest flying birds, and for the most part, they're geese.
50
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,
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according to our calculations, and this matches up pretty well with what scientists have actually observed.
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Like during its migration over the highest mountain range on the planet, the bar-headed goose can reach altitudes of over 7,000 meters.
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Then there's the white stork, which based on its popsicle point and lift limit, is our predicted highest flying bird.
54
It could potentially fly up to about 10,500 meters.
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In reality, it doesn't fly anywhere near that high.
56
But remember, birds don't necessarily fly as high as they might be physically capable of.
57
But wait, what about the Rupal's griffin?
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A bird we know for a fact can fly higher than 11,000 meters.
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Our math suggests that it is lift limited a lot lower than that, about 8200 meters.
60
But this is where theoretical calculations fall short without some additional real-world knowledge.
61
See, the RuPaul's Griffin likes to soar on thermals, warm columns of rising air that can help birds exceed their mathematical lift limit,
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sometimes even thousands of extra meters up into the air.
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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,
64
with the right thermal.
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It might even reach its very generous popsicle point of 15,000 meters.
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Turns out, that bird might have had a lot of climbing left to do.
67
You might have noticed that this video is chock full of all sorts of calculations
68
that I basically ripped my hair out trying to make sure I got right.
69
It would have been great if I had a brilliant tutor sitting next to me guiding my learning.
70
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71
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72
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73
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74
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75
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76
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77
Thanks Brilliant!
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Từ vựng và ghi chú luyện nói cho bài học này
Video này có 77 câu và 1297 từ để luyện shadowing. Phần lời nói dài 6:44. Người nói nói nhanh, khoảng 193 từ mỗi phút, nên sẽ có nhiều chỗ nối âm và nuốt âm. Chỉ 79% số từ nằm trong 3.000 từ tiếng Anh thông dụng nhất, nên từ vựng khá khó.
Từ vựng quan trọng trong video
15 từ đáng học trong video, kèm phiên âm và nghĩa:
| Từ | Phiên âm | Nghĩa |
|---|---|---|
| meter danh từ | /ˈmitəɹ/ | cái đo, người đo |
| oxygen danh từ | /ˈɑksɪd͡ʒən/ | ôxy, dưỡng khí |
| goose danh từ | /ɡus/ | ngỗng |
| generate động từ | /ˈd͡ʒɛn.ə.ɹeɪt/ | sinh ra, gây ra |
| calculation danh từ | /ˌkælkjuˈleɪʃn̩/ | tính toán |
| tutor danh từ | /ˈtjuːtəː/ | gia sư |
| angle danh từ | /ˈæŋ.ɡəl/ | gốc |
| estimate danh từ | /ˈɛs.tɪ.mət/ | ước lượng |
| biology danh từ | /baɪˈɑ.lə.d͡ʒi/ | sinh học, sinh vật học |
| depend động từ | /dɪˈpɛnd/ | phụ thuộc |
| decrease động từ | /dɪˈkɹiːs/ | hạ |
| mathematics danh từ | /mæθ(.ə)ˈmæt.ɪks/ | toán học |
| equation danh từ | /ɪˈkweɪ.ʒən/ | phương trình |
| dense tính từ | /ˈdɛns/ | đặc, dày đặc |
| wander động từ | /ˈwɑndɚ/ | lang thang |
Cụm động từ bạn sẽ nghe
| Từ | Nghĩa |
|---|---|
| take off động từ | bỏ |
Phát âm cần chú ý
Người nói dùng 15 dạng rút gọn, ví dụ don't, isn't, they're. Hãy nói theo dạng ngắn đúng như bạn nghe.
- Âm “th”: mathematics /mæθ(.ə)ˈmæt.ɪks/, mathematical /ˌmæθ(.ə)ˈmæt.ɪ.kəl/, thermal /ˈθɜːməl/, theoretical /ˌθi.əˈɹɛt.ɪ.kəl/, feather /ˈfɛðə/
- Âm “sh” và “zh”: calculation /ˌkælkjuˈleɪʃn̩/, potentially /pəˈtɛnʃ(ə)li/, equation /ɪˈkweɪ.ʒən/, explanation /ˌɛkspləˈneɪʃən/, exception /əkˈsɛpʃən/
- Từ dài — đặt trọng âm cho đúng: necessarily /ˌnɛs.əˈsɛɹ.ə.li/, potentially /pəˈtɛnʃ(ə)li/, biology /baɪˈɑ.lə.d͡ʒi/, mathematics /mæθ(.ə)ˈmæt.ɪks/, explanation /ˌɛkspləˈneɪʃən/
Cách luyện với video này
- Nghe hết video một lần, chưa cần nói, và ghi lại những từ bạn chưa biết.
- Bắt đầu ở tốc độ 0,75×, nói đuổi từng câu, rồi quay lại tốc độ bình thường khi đã quen.
- Ghi âm giọng mình rồi so với bản gốc, chú ý các từ như meter, oxygen, goose.
Phương Pháp Shadowing Là Gì?
Shadowing là kỹ thuật học ngôn ngữ có cơ sở khoa học, ban đầu được phát triển cho chương trình đào tạo phiên dịch viên chuyên nghiệp và được phổ biến rộng rãi bởi nhà đa ngôn ngữ học Dr. Alexander Arguelles. Nguyên lý cốt lõi đơn giản nhưng cực kỳ hiệu quả: bạn nghe tiếng Anh của người bản xứ và lặp lại to ngay lập tức — như một "cái bóng" (shadow) đuổi theo người nói với độ trễ chỉ 1–2 giây. Khác với luyện ngữ pháp hay học từ vựng bị động, Shadowing buộc não bộ và cơ miệng phải đồng thời xử lý và tái tạo ngôn ngữ thực tế. Các nghiên cứu khoa học xác nhận phương pháp này cải thiện đáng kể phát âm, ngữ điệu, nhịp điệu, nối âm, kỹ năng nghe và độ lưu loát khi nói — đặc biệt hiệu quả cho người luyện IELTS Speaking và muốn giao tiếp tiếng Anh tự nhiên như người bản ngữ.