Rockets火箭

火箭不是「推著空氣前進」——它在真空裡反而更有效率。牛頓第三運動定律解釋了一切。

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The Launch Site火箭發射場

12 個可以點的單字 · 可以隨時暫停、轉動場景

逐字稿（14 段）
  1. 1Welcome to the launch site. Today we will find out how a rocket gets into space.歡迎來到火箭發射場。今天來看看火箭是怎麼上太空的。
  2. 2This is a rocket. It works by throwing hot gas out of the back, very fast.這是一枚火箭。它的原理是把高溫氣體從後面用極快的速度噴出去。
  3. 3Every action has an equal reaction. Throw a ball backwards, and you roll forwards.每個作用力都有大小相等的反作用力。把球往後丟，你就往前滑。
  4. 4The two pushes are equal and opposite. Air rushes back, so the balloon rushes forward.兩個力大小相等、方向相反。空氣往後衝，氣球就往前衝。
  5. 5In an engine, hot gas rushes down and makes thrust. Thrust pushes the rocket up.引擎把高溫氣體往下噴，產生推力，推力把火箭往上推。
  6. 6Most of a rocket is fuel. Usually over ninety percent of the launch weight is propellant.火箭大部分是燃料，發射重量通常有九成以上是推進劑。
  7. 7A rocket carries its own oxygen, so its engine works where there is no air.火箭自己帶氧氣，所以在沒有空氣的地方引擎也能運作。
  8. 8A rocket does not push against the air. In the vacuum of space, it actually works better.火箭不是推著空氣前進。在太空的真空中，它反而更有效率。
  9. 9Rockets drop each stage when its tank is empty. So a rocket gets smaller on the way up.火箭每燒完一節就丟掉一節，所以它往上飛時會越變越小。
  10. 10Only a small part at the very top is the payload, like this satellite.真正的酬載只佔最頂端一小部分，像這顆人造衛星。
  11. 11Rockets launch towards the east. The Earth already spins that way, so they get a free head start.火箭往東發射。地球本來就往東轉，等於免費得到一個初速。
  12. 12That big white cloud is mostly water vapour, not smoke.那一大團白雲主要是水蒸氣，不是煙。
  13. 13This first stage came back and landed. Reusable rockets fly again, and that cuts the cost a lot.這一節飛回來降落了。可回收火箭能再飛一次，大幅降低成本。
  14. 14Rockets were invented in China about a thousand years ago. Now it's your turn. Click and explore!火箭大約一千年前在中國發明。現在換你了，點點看、到處逛逛吧！

Push Something Backwards把東西往後推

A rocket works by throwing mass out of the back very fast. Newton's third law says every action has an equal and opposite reaction.火箭的原理是把質量以極高速度從後方拋出。牛頓第三定律說：每個作用力都有大小相等、方向相反的反作用力。

So when hot gas rushes backwards, the rocket is pushed forwards by exactly the same amount of force.所以當高溫氣體向後衝出，火箭就被同樣大小的力往前推。

People sometimes think a rocket pushes against the air. It does not — and in space, with no air pushing back, a rocket is actually more efficient.有人以為火箭是推著空氣前進。並不是——而且在太空中沒有空氣阻礙，火箭反而更有效率。

The hard part is not going up. It is going sideways fast enough to stay in orbit.困難的不是往上飛，而是橫向飛得夠快，才能維持在軌道上。

Why Getting to Orbit Is Hard為什麼進入軌道這麼難

Orbit is sideways speed軌道是橫向速度
To orbit is to fall towards Earth and keep missing, because you are moving sideways so fast. That needs about 28,000 kilometres per hour.在軌道上就是一直朝地球墜落卻一直錯過，因為你橫向移動得太快。這需要大約時速 28,000 公里。
Most of the rocket is fuel火箭大部分是燃料
Typically over ninety percent of the launch weight is propellant. Only a small fraction at the very top is the actual payload.發射重量通常有九成以上是推進劑。真正的酬載只佔最頂端很小一部分。
Stages are thrown away分節丟棄
Carrying an empty fuel tank wastes energy, so rockets drop each stage as it empties. That is why a rocket gets smaller on the way up.帶著空油箱是浪費能量，所以火箭燒完一節就丟一節。這就是為什麼火箭上升途中會越變越小。
Launch eastwards向東發射
The Earth already spins eastwards, so launching that way gives a free head start. Sites near the equator get the biggest boost.地球本來就向東自轉，所以往東發射等於免費得到一個初速。越靠近赤道的發射場得到的加成越大。
Reusable rockets可回收火箭
Landing the first stage and flying it again cuts cost dramatically, in the same way an airline could not survive if it threw away the plane after each flight.把第一節回收再飛可以大幅降低成本——就像航空公司如果每飛一趟就丟掉一架飛機，根本活不下去。

Speeds You Need需要的速度

Goal 目標Speed 速度
Stay in low Earth orbit 進入近地軌道About 28,000 km/h 約時速 28,000 公里
Escape Earth's gravity 脫離地球重力About 40,000 km/h 約時速 40,000 公里
A passenger jet 客機About 900 km/h 約時速 900 公里
A rifle bullet 步槍子彈About 3,000 km/h 約時速 3,000 公里

資料查證至 2025 年底

進入軌道所需的速度大約是步槍子彈的九倍。這就是為什麼火箭要那麼大——絕大部分的能量花在「橫向加速」，不是「往上爬」。

Did You Know?你知道嗎？

  • Rockets were invented in China around a thousand years ago, using gunpowder in bamboo tubes.火箭大約一千年前在中國發明，用竹管裝火藥。
  • The Saturn V that carried astronauts to the Moon is still the tallest and most powerful rocket ever flown successfully.載太空人上月球的農神五號，至今仍是成功飛行過最高、最強的火箭。
  • A rocket engine carries its own oxygen, which is why it works where there is no air.火箭引擎自己帶氧氣，這就是它在沒有空氣的地方也能運作的原因。
  • The white cloud behind a launching rocket is mostly water vapour, not smoke.火箭升空後方那團白雲主要是水蒸氣，不是煙。

Key Words單字表

  • rocket/ˈrɑː.kɪt/n.

    火箭

    The rocket lifted off at dawn.火箭在破曉時升空。

  • thrust/θrʌst/n.

    推力

    The engines produce huge thrust.引擎產生巨大的推力。

  • reaction/riˈæk.ʃən/n.

    反作用

    Every action has a reaction.每個作用力都有反作用力。

  • opposite/ˈɑː.pə.zɪt/adj.

    相反的

    Equal and opposite.大小相等、方向相反。

  • fuel/fjuːl/n.

    燃料

    Most of the weight is fuel.大部分重量是燃料。

  • stage/steɪdʒ/n.

    節、級

    The first stage falls away.第一節會脫落。

  • payload/ˈpeɪ.loʊd/n.

    酬載

    The payload sits at the top.酬載在最頂端。

  • launch/lɑːntʃ/v. / n.

    發射

    They launch eastwards.他們往東發射。

  • reusable/ˌriːˈjuː.zə.bəl/adj.

    可重複使用的

    Reusable rockets cut costs.可回收火箭降低成本。

  • vacuum/ˈvæk.juːm/n.

    真空

    A rocket works in a vacuum.火箭在真空中也能運作。

  • oxygen/ˈɑːk.sɪ.dʒən/n.

    氧氣

    It carries its own oxygen.它自己帶氧氣。

  • vapour/ˈveɪ.pɚ/n.

    蒸氣

    The cloud is water vapour.那團雲是水蒸氣。

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