The downstroke下拍
The wings are halfway down. Compare the orange arrow with the gray one.
翅膀拍到一半。比一比橘色箭頭和灰色箭頭。
Living Things · Unit 3 · Lesson 9 · 生命與生態 單元三 第九課
How Does a Bird Fly?鳥為什麼會飛？
A bird is heavier than air, just as you are. It stays up because almost everything about its body has been shaped for flying. In a 3D model, slow down one beat of the wings and watch four forces change: lift, weight, thrust, and drag. Look inside at the muscles that do the work. Then stop flapping, and see how a bird can still climb without moving its wings at all. Last, match four wing shapes to four ways of flying.
鳥比空氣重，就和你一樣。牠能留在空中，是因為牠身上幾乎每一個地方都是為了飛行而長成那樣的。在 3D 模型裡，把拍一下翅膀的動作放慢，看四個力怎麼變化：升力、重量、推力和阻力。看看身體裡面出力的肌肉。接著停止拍翅，看一隻鳥怎麼連翅膀都不動也能往上升。最後把四種翅膀的形狀，和四種飛法配起來。
Big idea · 一句話看懂
A wing moving through the air is pushed upward. That push is called lift. When a bird beats its wings down, it also gets a push forward. On the way up it folds its wings a little, so the upstroke costs less. A bird's whole body is built for this, with hollow bones, feathers that lock together, and huge breast muscles. And a bird does not always need to flap. With its wings held out it can glide, or ride on warm rising air.
翅膀在空氣中前進，就會被往上推，這股力叫做升力。鳥往下拍翅膀的時候，還會多得到一股往前的推力；往上舉的時候把翅膀收起來一點，這樣比較省力。鳥的全身都是為了這件事而打造的：空心的骨頭、可以互相扣住的羽毛，還有非常發達的胸肌。而且鳥不一定要一直拍翅；把翅膀張開，牠可以滑翔，也可以乘著上升的熱空氣。
3D Model · 3D 模型
One Beat of the Wings 拍一下翅膀
Drag to turn the model, and scroll or pinch to zoom. The bird stays in the middle, and the white streaks show the air going past. Press Pause, and move the Wingbeat slider slowly through one beat. Watch the orange arrow. When is it long, and when does it almost vanish? Switch on See inside to find the muscles. Then choose Gliding, and then Riding warm air.
拖曳可以旋轉模型，滾輪或雙指可以縮放。鳥一直在畫面中間，白色的短線是流過的空氣。按「暫停」，把「拍翅」滑桿慢慢拉過一個完整的拍動。盯著橘色的箭頭：它什麼時候很長，什麼時候幾乎不見？打開「看裡面」找一找肌肉。然後選「滑翔」，再選「乘著熱氣流」。
Drag to turn · 拖曳旋轉 Scroll or pinch to zoom · 滾輪／雙指縮放
This 3D model needs WebGL, which this browser does not support. The reading and the cards below still explain everything.
這個瀏覽器不支援 WebGL，無法顯示 3D 模型；下方的課文與卡片一樣能看懂。
- Blue arrow: lift, up
藍色箭頭：升力，往上 - White arrow: weight, down
白色箭頭：重量，往下 - Orange arrow: thrust, forward
橘色箭頭：推力，往前 - Gray arrow: drag, backward
灰色箭頭：阻力，往後 - Red: the breast muscles, for the downstroke
紅色：胸肌，負責下拍 - Pink: the smaller muscles, for the upstroke
粉紅色：較小的肌肉，負責上舉
A teaching model. The lengths of the arrows are examples that show which force is larger and when. They are not measurements. A real wing twists and changes shape all through the beat, far more than these two flat pieces can show. Real birds beat their wings much faster than the model does. The bird is drawn as a simple shape and is not any one species.
這是教學用的模型。箭頭的長短是示意，只表示哪個力比較大、在什麼時候比較大，不是量出來的數字。真的翅膀在拍動的過程中會不停地扭轉、變形，遠比這兩片平板複雜。真的鳥拍翅也比模型快得多。這隻鳥畫成簡單的形狀，並不是哪一種特定的鳥。
Model drawn by My Culture Connect as a teaching diagram. The ideas follow the sources listed at the bottom of this page. · 模型由人師教育協會自繪示意；原理依本頁最下方列出的出處。
Reading · 英文閱讀
9
Unit 9: How Does a Bird Fly?
Hold your hand flat in the wind from a fan, with the front edge tipped up a little. You will feel the air push your hand upward. A bird's wing does the same thing, but it does it much better. The upward push is called lift.
把手掌攤平，放在電風扇吹出來的風裡，前緣稍微往上翹。你會感覺到空氣把你的手往上推。鳥的翅膀做的是同一件事，只是做得好太多了。這股往上的力，叫做升力。
Lift only comes when air is flowing over the wing, so a bird has to keep moving forward. That is what flapping is for. When the wings beat down, they push air down and back, and the bird is pushed up and forward. On the way up, the wings fold in a little, so that they do not push the bird back down.
要有空氣流過翅膀才會有升力，所以鳥必須一直往前移動。拍翅就是為了這個。翅膀往下拍的時候，把空氣往下、往後推，鳥就被往上、往前推。往上舉的時候，翅膀會稍微收起來，免得把自己又推回下面去。
Flapping is hard work, and a bird's body is built for it. Many of its bones are hollow, with thin struts inside to keep them strong. Its breastbone has a deep ridge called a keel, and the flight muscles are fixed to it. In many birds those muscles make up a quarter or more of the whole body.
拍翅很費力，而鳥的身體就是為此打造的。牠有很多骨頭是空心的，裡面有細細的支柱來保持強度。牠的胸骨上有一道很深的突起，叫做龍骨，飛行用的肌肉就固定在上面。很多鳥的這些肌肉，佔了全身重量的四分之一以上。
Feathers matter just as much. Each one is light and stiff. Its tiny branches hook on to one another like a zipper, so the wing makes a smooth surface that air cannot slip through. A bird keeps its feathers in order by running them through its beak.
羽毛也一樣重要。每一根都又輕又挺，上面細小的分支像拉鍊一樣互相鉤住，所以翅膀能形成一個空氣鑽不過去的平滑表面。鳥會用嘴一根一根地梳理羽毛，讓它們保持整齊。
A bird does not have to flap all the time. With its wings held out, it can glide, slowly losing height as it goes. And if it finds a place where warm air is rising, it can circle inside it and be carried upward for nothing. Eagles and hawks travel great distances this way.
鳥不必一直拍翅。把翅膀張開，牠可以滑翔，一路慢慢降低高度。要是找到一處熱空氣正在上升的地方，牠可以在裡面盤旋，免費被帶上高空。鵰和鷹就是這樣飛很遠的路。
Wings come in different shapes for different lives. Short, rounded wings are good for quick turns among trees. Long, narrow wings are good for gliding over the sea for hours. You can often tell how a bird lives just by looking at the shape of its wings.
不同的生活方式，有不同形狀的翅膀。又短又圓的翅膀，適合在樹林間急轉彎；又長又窄的翅膀，適合在海上一連滑翔好幾個小時。光看一隻鳥翅膀的形狀，常常就猜得出牠怎麼過日子。
Read aloud · 課文朗讀
Questions · 閱讀理解
What is lift?
The upward push that air gives to a wing moving through it.
Why do a bird's wings fold a little on the way up?
So that they catch less air and do not push the bird back down.
How can a bird climb without flapping?
It circles inside warm air that is rising, and the air carries it up.
Words & Phrases · 生字及片語
bird(n.)鳥A bird landed on the fence.一隻鳥停在圍籬上。wing(n.)翅膀The eagle spread its wings.老鷹張開了翅膀。feather(n.)羽毛A feather is light but strong.羽毛很輕，卻很堅韌。flap(v.)拍動（翅膀）Small birds flap their wings very fast.小鳥拍翅膀拍得很快。glide(v.)滑翔The hawk glides without moving its wings.那隻鷹翅膀不動地滑翔。muscle(n.)肌肉Flying takes strong muscles.飛行需要強壯的肌肉。hollow(adj.)空心的Many bird bones are hollow.鳥有很多骨頭是空心的。lift(n. / v.)升力；舉起Air moving over a wing gives lift.流過翅膀的空氣產生升力。
Quick Check · 小測驗
1. What is lift?
2. Which part of a wingbeat gives most of the push forward?
3. Why are many of a bird's bones hollow?
4. What is the keel?
5. How does a soaring hawk gain height without flapping?
Read a Wing · 看懂翅膀
Four wings for four ways of life 四種翅膀，四種生活
Choose a wing shape, and find out what it is good at and which birds have it.
選一種翅膀的形狀，看它擅長什麼、哪些鳥有這種翅膀。
Choose a wing · 選一種翅膀
The shapes are rough sketches. Real wings fall in between these four kinds, and one bird can change the shape of its wing as it flies.這些形狀只是粗略的示意。真的翅膀常常介於這四類之間，而且同一隻鳥在飛行中也會改變翅膀的形狀。
This wing is good for · 這種翅膀擅長
Try It in the Model · 在模型裡試試
Four things to watch 四件值得看的事
Over one whole beat, the long blue arrow of the downstroke and the short one of the upstroke average out to match the weight. That is why the bird stays level.
把一整個拍動平均起來，下拍時很長的藍色箭頭和上舉時很短的藍色箭頭，剛好抵得過重量。所以這隻鳥能維持平飛。
The upstroke上舉
Look at the outer half of each wing. What has it done, and why?
看看每一邊翅膀的外半段。它做了什麼？為什麼？
The flight muscles飛行的肌肉
Two sets of muscles take turns. Watch which one lights up on each half of the beat.
兩組肌肉輪流出力。看看拍動的每一半是哪一組亮起來。
Riding warm air乘著熱氣流
The orange dots are warm air going up. The bird is rising, and its wings are still.
橘色的小點是往上升的熱空氣。鳥在上升，翅膀卻沒有動。
Go Further · 延伸閱讀
A machine that copies the wing, and the air that rises 學翅膀的機器，還有會上升的空氣
How Things Work · Lesson 13 · 萬物原理 第十三課How Does an Airplane Stay in the Air?飛機為什麼飛得起來？See the same four forces on a wing that does not flap.在一片不會拍動的機翼上，看同樣的四個力。Go to the lesson · 前往這一課 →Earth and Weather · Lesson 7 · 地球與天氣 第七課Why Does the Wind Blow?風是怎麼來的？Find out why warm air rises in the first place.先弄懂熱空氣為什麼會上升。Go to the lesson · 前往這一課 →
Flight by the Numbers · 飛行的數字
Six numbers about bird flight 六個和鳥類飛行有關的數字
How strong, how wide, how fast, and how long.
多有力、多寬、多快、多久。
25–40%of body weight · 的體重
A bird's two sets of flight muscles together make up about this much of its whole body.鳥的兩組飛行肌加起來，大約佔全身重量的這麼多。
3.7 mwingspan · 翼展
The snowy albatross has the longest wings of any living bird, up to this far from tip to tip.漂泊信天翁的翅膀是現存鳥類裡最長的，兩邊翼尖之間可以這麼寬。
99beats a second · 次／秒
Small hummingbirds beat their wings up to this fast when they hover. The largest ones manage about 12.小型的蜂鳥懸停時，翅膀每秒最多可以拍這麼多下；最大的蜂鳥大約 12 下。
10months · 個月
Some common swifts stay in the air this long without landing. They eat and sleep on the wing.有些普通雨燕可以連續這麼久不落地，吃和睡都在空中。
175muscles · 條肌肉
Most birds have about this many different muscles, mainly for the wings, skin, and legs.大部分的鳥大約有這麼多條不同的肌肉，主要控制翅膀、皮膚和腳。
9,000 kma year · 一年
The average round trip of the gray-faced buzzards that pass over Taiwan each spring and autumn.每年春秋兩季經過台灣的灰面鵟鷹，來回遷移的平均距離。
Flight Stories · 飛行的故事
A zipper, a pulley, a bird that never lands, and hawks over Bagua Mountain 拉鍊、滑輪、不落地的鳥，還有八卦山上的鷹
Four pieces of the answer to how birds stay up.
鳥為什麼能留在空中——四塊拼圖。
Feather · 羽毛
The zipper in a feather羽毛裡的拉鍊
Look at a feather through a magnifying glass. From the central shaft, hundreds of thin branches run out to each side. Each branch has even finer branches with tiny hooks on them, and the hooks catch on the branch next door. That is what holds the feather together as one smooth sheet. Feathers also keep a bird warm and help to keep it dry.
用放大鏡看一根羽毛。從中間的羽軸往兩邊，伸出好幾百條細細的分支；每一條分支上又有更細的小分支，上面帶著小小的鉤子，鉤住隔壁的那一條。整根羽毛就是這樣連成一片平滑的面。羽毛還能替鳥保暖，也有助於防水。
Shoulder · 肩膀
Lifting a wing from below從下面把翅膀舉起來
You might expect the muscle that lifts the wing to sit on a bird's back. It does not. Both sets of flight muscles lie under the bird, on its breast. The one that raises the wing has a long cord that runs up through the shoulder, over the bone, and down onto the top of the wing bone. When the muscle pulls down, the wing goes up, like a flag on a rope.
你可能會以為，把翅膀舉起來的肌肉長在鳥的背上。其實不是。兩組飛行肌都在鳥的下方、胸部的位置。負責把翅膀舉起來的那一組，有一條長長的腱，往上穿過肩膀、繞過骨頭，再接到翅膀骨頭的上面。肌肉往下拉，翅膀就往上——像用繩子升旗一樣。
Swift · 雨燕
Ten months in the air在空中十個月
The common swift is a small bird with long, curved, pointed wings. It catches insects in flight, drinks in flight, and sleeps in flight. Scientists who fitted swifts with tiny recorders found that some of them did not land once in ten months. They came down only to nest.
普通雨燕是一種小鳥，翅膀又長又尖、彎彎的。牠在飛行中捕食昆蟲、在飛行中喝水，也在飛行中睡覺。科學家替雨燕裝上很小的記錄器之後發現，有些雨燕在十個月裡一次也沒有降落，只有築巢的時候才下來。
Taiwan · 台灣
The rising hawks of Bagua Mountain八卦山的起鷹
Each March and April, gray-faced buzzards cross Taiwan on their way north to nest, and thousands of them rest for the night on Bagua Mountain in Changhua. Early in the morning the air is still, and the hawks have to flap as they leave the trees. As the sun grows stronger, the ground warms and the air above it begins to rise. Then the hawks spread their wings and circle upward together in a great turning column. Because they arrive around Tomb-Sweeping Day, they are also called the Qingming birds.
每年三、四月，灰面鵟鷹往北返回繁殖地的途中經過台灣，成千上萬隻在彰化的八卦山上過夜休息。清晨空氣對流還很弱，鷹群離開樹林時得拍著翅膀飛。等陽光愈來愈強，地面變暖，上方的空氣開始上升，鷹群就張開翅膀，一起盤旋而上，形成一根旋轉的「鷹柱」。因為牠們在清明前後抵達，所以又被叫做「清明鳥」。
Myth vs. Fact · 常見迷思
Four things people get wrong 四個常見的誤會
✗ Myth · 迷思Birds have to flap all the time to stay up.鳥要一直拍翅膀才不會掉下來。
✓ Fact · 事實Many birds glide for long stretches, and some climb on rising air without flapping at all.很多鳥可以滑翔很長一段；有些還能乘著上升的空氣往上升，完全不用拍翅。
✗ Myth · 迷思Hollow bones are weak bones.空心的骨頭很脆弱。
✓ Fact · 事實They are braced inside with thin struts, which keep them strong.它們裡面有細細的支柱撐著，所以很堅固。
✗ Myth · 迷思The upstroke pushes the bird back down as much as the downstroke lifts it.翅膀往上舉的時候，會把鳥往下推，剛好抵消下拍。
✓ Fact · 事實The wings fold in on the way up, so they push against far less air.往上舉的時候翅膀會收起來，推到的空氣少得多。
✗ Myth · 迷思Feathers are only for flying.羽毛只是用來飛的。
✓ Fact · 事實They also keep a bird warm and help to keep it dry.羽毛也替鳥保暖，並且有助於防水。
Remember It · 記憶口訣
Flight in a sentence 一句話記住飛行
Moving air lifts a wing流動的空氣把翅膀抬起來
So a bird must keep moving forward.
所以鳥得一直往前。
Down pushes, up folds下拍用力，上舉收翅
Most of the thrust comes from the downstroke.
推力大部分來自下拍。
A body built to fly為了飛而打造的身體
Hollow bones, a keel, big muscles.
空心的骨頭、龍骨、大塊肌肉。
No flapping needed不拍也能飛
Glide, or ride rising air.
滑翔，或乘著上升的空氣。
An Observer's Code · 觀察守則
Watching birds without disturbing them 看鳥，但不打擾牠們
- Watch from a distance. If a bird stops what it is doing and looks at you, you are too close.保持距離。要是鳥停下原本在做的事、盯著你看，就表示你靠得太近了。
- Never go near a nest, and never pick up a young bird that seems to be alone. Its parents are usually close by.不要靠近鳥巢；看到好像落單的幼鳥也不要撿，牠的爸媽通常就在附近。
- Do not feed wild birds, and keep your voice low.不要餵野鳥，說話放輕聲。
Classroom Activity 1 · 課堂活動一
Lift on a Strip of Paper 紙條上的升力
You need · 準備材料
- A strip of paper about 3 centimeters wide and 20 centimeters long一張大約 3 公分寬、20 公分長的紙條
- A pencil and a piece of tape一支鉛筆和一段膠帶
Steps · 步驟
- Tape one end of the strip along the pencil so that the rest hangs down like a flag.把紙條的一端貼在鉛筆上，讓其餘的部分像旗子一樣垂下來。
- Hold the pencil just under your lower lip, with the strip hanging away from you.把鉛筆拿在下唇的正下方，讓紙條朝外垂著。
- Blow hard across the top of the strip. What does it do?對著紙條的上方用力吹氣。它怎麼了？
- Now tilt the pencil so that the strip starts at different angles, and find the angle where it rises most easily.接著轉動鉛筆，讓紙條一開始的角度不一樣，找出它最容易飄起來的角度。
The strip rises into the stream of air. A wing is shaped and tilted so that the air flowing past it pushes it up in the same way.
紙條會往上飄進那股氣流裡。翅膀的形狀和傾斜的角度，就是為了讓流過的空氣用同樣的方式把它往上推。
Classroom Activity 2 · 課堂活動二
Wing Watching 看翅膀
You need · 準備材料
- A notebook and a pencil一本筆記本和一支鉛筆
- A place where you can see birds flying, such as a park, a field, or a riverbank一個看得到鳥在飛的地方，例如公園、田邊或河堤
Steps · 步驟
- Choose one bird in flight and watch it for as long as you can.選一隻正在飛的鳥，盡可能看久一點。
- Draw the shape of its wings: short or long, rounded or pointed.畫下牠翅膀的形狀：短的還是長的？圓的還是尖的？
- Write down how it flies. Does it flap all the time, flap and then glide, or circle without flapping?記下牠怎麼飛：一直拍翅？拍幾下再滑翔？還是不拍翅地盤旋？
- Do this for three different kinds of bird. Does the wing shape match the way of flying?找三種不同的鳥各做一次。翅膀的形狀和飛法對得起來嗎？
Egrets, swallows, and sparrows are good ones to compare. On a warm, sunny morning, look high up for larger birds turning in circles.
白鷺鷥、燕子和麻雀很適合拿來比較。晴朗溫暖的上午，往高處找找有沒有在繞圈的大型鳥。
Sources · 資料出處
Facts and numbers on this page were checked against these sources (October 2026). · 本頁的事實與數字依下列資料查證（2026 年 10 月）。
- Lift is produced by air flowing over the wing, which is an airfoil; flapping has a downstroke, which provides most of the thrust, and an upstroke, during which the wing is slightly folded inward; in gliding no propulsion is used and the bird descends unless it is in rising air; wing shapes fall into four broad types (elliptical, high speed, high aspect ratio, and soaring wings with deep slots), with the example birds given for each升力來自流過翅膀（翼型）的空氣；拍翅分為下拍（提供大部分推力）與上舉（翅膀略向內收）；滑翔不使用推進力，除非在上升氣流中，否則會下降；翅膀形狀大致分四類（橢圓翼、高速翼、高展弦比翼、有深翼縫的翱翔翼），各類的代表鳥種Wikipedia, “Bird flight” ↗
- Birds have many hollow bones with criss-crossing struts for strength; the pectorals provide the powerful downstroke and the supracoracoideus, lying under them, lifts the wing through a pulley-like system; together they make up about 25–40% of the body weight; most birds have about 175 muscles鳥有許多空心的骨頭，內有交叉的支柱以維持強度；胸肌負責有力的下拍，位於其下方的上喙肌以類似滑輪的方式舉起翅膀；兩者合計約佔體重 25–40%；多數鳥約有 175 條肌肉Wikipedia, “Bird anatomy” ↗
- The keel is an extension of the breastbone that runs along its midline龍骨是胸骨沿中線延伸出的突起Wikipedia, “Keel (bird anatomy)” ↗
- Feathers aid in flight, thermal insulation, and waterproofing; interlocking barbules hold the vane together羽毛有助於飛行、保溫與防水；互相扣合的羽小枝讓羽片連成一片Wikipedia, “Feather” ↗
- The snowy (wandering) albatross has the longest wingspan of any living bird, up to 3.7 m漂泊信天翁是現存翼展最長的鳥，可達 3.7 公尺Wikipedia, “Snowy albatross” ↗
- Hummingbirds hover with wingbeats from about 12 per second in the largest species to 99 per second in small ones蜂鳥懸停時的拍翅頻率，從最大種類的每秒約 12 次到小型種類的每秒 99 次Wikipedia, “Hummingbird” ↗
- Common swifts drink, feed, and often sleep on the wing; some individuals go 10 months without landing普通雨燕在飛行中喝水、覓食，也常在飛行中睡覺；有些個體可以 10 個月不落地Wikipedia, “Common swift” ↗
- Gray-faced buzzards pass Bagua Mountain from March to April on their way north, resting there in the thousands; their round trip averages about 9,000 km; at dawn, when convection is weak, they flap, and as the sunlight strengthens and warm air rises they circle up on it; they are called the birds of Tomb-Sweeping Day灰面鵟鷹 3 月到 4 月北返時過境八卦山，成千上萬隻在此短暫停留；來回遷移距離平均約 9,000 公里；清晨對流弱時拍翅起飛，陽光漸強、熱氣上升後隨氣流盤旋（起鷹）；又稱「清明鳥」「南路鷹」交通部觀光署參山國家風景區管理處〈關於八卦山賞鷹〉 Tri-Mountain National Scenic Area Administration, Taiwan ↗